Android samples are updated: onPause()/onResume() release/open camera, a message is shown on camera open error, minor fixes in code and resources

samples/android/15-puzzle/src/org/opencv/samples/puzzle15/SampleCvViewBase.java

@@ -26,13 +26,36 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        synchronized (this) {
+	        releaseCamera();
+	        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
+	        if (!mCamera.isOpened()) {
+	            mCamera.release();
+	            mCamera = null;
+	            Log.e(TAG, "Failed to open native camera");
+	            return false;
+	        }
+	    }
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        synchronized (this) {
+	        if (mCamera != null) {
+	                mCamera.release();
+	                mCamera = null;
+            }
+        }
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera("+width+", "+height+")");
         synchronized (this) {
             if (mCamera != null && mCamera.isOpened()) {
-                Log.i(TAG, "before mCamera.getSupportedPreviewSizes()");
                 List<Size> sizes = mCamera.getSupportedPreviewSizes();
-                Log.i(TAG, "after mCamera.getSupportedPreviewSizes()");
                 int mFrameWidth = width;
                 int mFrameHeight = height;
 
@@ -52,28 +75,22 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
                 mCamera.set(Highgui.CV_CAP_PROP_FRAME_HEIGHT, mFrameHeight);
             }
         }
+
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
     }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
-        if (mCamera.isOpened()) {
         (new Thread(this)).start();
-        } else {
-            mCamera.release();
-            mCamera = null;
-            Log.e(TAG, "Failed to open native camera");
-        }
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        if (mCamera != null) {
+        releaseCamera();
-            synchronized (this) {
-                mCamera.release();
-                mCamera = null;
-            }
-        }
     }
 
     protected abstract Bitmap processFrame(VideoCapture capture);

samples/android/15-puzzle/src/org/opencv/samples/puzzle15/puzzle15Activity.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.puzzle15;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Menu;
@@ -18,6 +20,31 @@ public class puzzle15Activity extends Activity {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {

samples/android/15-puzzle/src/org/opencv/samples/puzzle15/puzzle15View.java

@@ -45,12 +45,12 @@ public class puzzle15View extends SampleCvViewBase implements OnTouchListener {
     }
 
     @Override
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+	public void surfaceCreated(SurfaceHolder holder) {
-        super.surfaceChanged(_holder, format, width, height);
         synchronized (this) {
             // initialize Mat before usage
             mRgba = new Mat();
         }
+		super.surfaceCreated(holder);
 	}
 
     public static void shuffle(int[] array) {
@@ -185,6 +185,8 @@ public class puzzle15View extends SampleCvViewBase implements OnTouchListener {
     }
 
     public boolean onTouch(View v, MotionEvent event) {
+        if(mRgba==null) return false;
+        
     	int cols = mRgba.cols();
         int rows = mRgba.rows();
         float xoffset = (getWidth() - cols) / 2;

samples/android/color-blob-detection/src/org/opencv/samples/colorblobdetect/ColorBlobDetectionActivity.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.colorblobdetect;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Window;
@@ -15,6 +17,31 @@ public class ColorBlobDetectionActivity extends Activity {
 		Log.i(TAG, "Instantiated new " + this.getClass());
 	}
 	
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {        

samples/android/color-blob-detection/src/org/opencv/samples/colorblobdetect/ColorBlobDetectionView.java

@@ -56,12 +56,13 @@ public class ColorBlobDetectionView extends SampleCvViewBase implements OnTouchL
 	}
 	
     @Override
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public void surfaceCreated(SurfaceHolder holder) {
-        super.surfaceChanged(_holder, format, width, height);
         synchronized (this) {
             // initialize Mat before usage
             mRgba = new Mat();
         }
+        
+        super.surfaceCreated(holder);
     }
 	
 	public boolean onTouch(View v, MotionEvent event)

samples/android/color-blob-detection/src/org/opencv/samples/colorblobdetect/SampleCvViewBase.java

@@ -26,13 +26,36 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        synchronized (this) {
+	        releaseCamera();
+	        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
+	        if (!mCamera.isOpened()) {
+	            mCamera.release();
+	            mCamera = null;
+	            Log.e(TAG, "Failed to open native camera");
+	            return false;
+	        }
+	    }
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        synchronized (this) {
+	        if (mCamera != null) {
+	                mCamera.release();
+	                mCamera = null;
+            }
+        }
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera");
         synchronized (this) {
             if (mCamera != null && mCamera.isOpened()) {
-                Log.i(TAG, "before mCamera.getSupportedPreviewSizes()");
                 List<Size> sizes = mCamera.getSupportedPreviewSizes();
-                Log.i(TAG, "after mCamera.getSupportedPreviewSizes()");
                 int mFrameWidth = width;
                 int mFrameHeight = height;
 
@@ -52,28 +75,22 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
                 mCamera.set(Highgui.CV_CAP_PROP_FRAME_HEIGHT, mFrameHeight);
             }
         }
+
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
     }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
-        if (mCamera.isOpened()) {
         (new Thread(this)).start();
-        } else {
-            mCamera.release();
-            mCamera = null;
-            Log.e(TAG, "Failed to open native camera");
-        }
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        if (mCamera != null) {
+        releaseCamera();
-            synchronized (this) {
-                mCamera.release();
-                mCamera = null;
-            }
-        }
     }
 
     protected abstract Bitmap processFrame(VideoCapture capture);

samples/android/face-detection/src/org/opencv/samples/fd/FdActivity.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.fd;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Menu;
@@ -15,19 +17,47 @@ public class FdActivity extends Activity {
     private MenuItem            mItemFace30;
     private MenuItem            mItemFace20;
     
+    private FdView				mView;
+
     public static float         minFaceSize = 0.5f;
 
     public FdActivity() {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         Log.i(TAG, "onCreate");
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
-        setContentView(new FdView(this));
+        mView = new FdView(this);
+        setContentView(mView);
     }
 
     @Override

samples/android/face-detection/src/org/opencv/samples/fd/FdView.java

@@ -62,14 +62,14 @@ class FdView extends SampleCvViewBase {
     }
 
     @Override
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+	public void surfaceCreated(SurfaceHolder holder) {
-        super.surfaceChanged(_holder, format, width, height);
-
         synchronized (this) {
             // initialize Mats before usage
             mGray = new Mat();
             mRgba = new Mat();
         }
+
+        super.surfaceCreated(holder);
 	}
 
 	@Override

samples/android/face-detection/src/org/opencv/samples/fd/SampleCvViewBase.java

@@ -28,13 +28,36 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        synchronized (this) {
+	        releaseCamera();
+	        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
+	        if (!mCamera.isOpened()) {
+	            mCamera.release();
+	            mCamera = null;
+	            Log.e(TAG, "Failed to open native camera");
+	            return false;
+	        }
+	    }
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        synchronized (this) {
+	        if (mCamera != null) {
+	                mCamera.release();
+	                mCamera = null;
+            }
+        }
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera("+width+", "+height+")");
         synchronized (this) {
             if (mCamera != null && mCamera.isOpened()) {
-                Log.i(TAG, "before mCamera.getSupportedPreviewSizes()");
                 List<Size> sizes = mCamera.getSupportedPreviewSizes();
-                Log.i(TAG, "after mCamera.getSupportedPreviewSizes()");
                 int mFrameWidth = width;
                 int mFrameHeight = height;
 
@@ -54,28 +77,22 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
                 mCamera.set(Highgui.CV_CAP_PROP_FRAME_HEIGHT, mFrameHeight);
             }
         }
+
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
     }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
-        if (mCamera.isOpened()) {
         (new Thread(this)).start();
-        } else {
-            mCamera.release();
-            mCamera = null;
-            Log.e(TAG, "Failed to open native camera");
-        }
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        if (mCamera != null) {
+        releaseCamera();
-            synchronized (this) {
-                mCamera.release();
-                mCamera = null;
-            }
-        }
     }
 
     protected abstract Bitmap processFrame(VideoCapture capture);

samples/android/image-manipulations/src/org/opencv/samples/imagemanipulations/ImageManipulationsActivity.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.imagemanipulations;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Menu;
@@ -8,7 +10,8 @@ import android.view.MenuItem;
 import android.view.Window;
 
 public class ImageManipulationsActivity extends Activity {
-    private static final String TAG = "Sample::Activity";
+
+	private static final String TAG = "Sample-ImageManipulations::Activity";
 
     public static final int     VIEW_MODE_RGBA  = 0;
     public static final int     VIEW_MODE_HIST  = 1;
@@ -30,17 +33,45 @@ public class ImageManipulationsActivity extends Activity {
 
     public static int           viewMode = VIEW_MODE_RGBA;
     
+    private ImageManipulationsView mView;
+
     public ImageManipulationsActivity() {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         Log.i(TAG, "onCreate");
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
-        setContentView(new ImageManipulationsView(this));
+        mView = new ImageManipulationsView(this);
+        setContentView(mView);
     }
 
     @Override

samples/android/image-manipulations/src/org/opencv/samples/imagemanipulations/ImageManipulationsView.java

@@ -55,9 +55,7 @@ class ImageManipulationsView extends SampleCvViewBase {
     }
 
     @Override
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+	public void surfaceCreated(SurfaceHolder holder) {
-        super.surfaceChanged(_holder, format, width, height);
-
         synchronized (this) {
             // initialize Mats before usage
             mGray = new Mat();
@@ -83,6 +81,8 @@ class ImageManipulationsView extends SampleCvViewBase {
             mP1 = new Point();
             mP2 = new Point();
         }
+
+        super.surfaceCreated(holder);
 	}
 
 	private void CreateAuxiliaryMats() {

samples/android/image-manipulations/src/org/opencv/samples/imagemanipulations/SampleCvViewBase.java

@@ -14,7 +14,7 @@ import android.view.SurfaceHolder;
 import android.view.SurfaceView;
 
 public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHolder.Callback, Runnable {
-    private static final String TAG = "Sample::SurfaceView";
+    private static final String TAG = "Sample-ImageManipulations::SurfaceView";
 
     private SurfaceHolder       mHolder;
     private VideoCapture        mCamera;
@@ -28,13 +28,36 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        synchronized (this) {
+	        releaseCamera();
+	        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
+	        if (!mCamera.isOpened()) {
+	            mCamera.release();
+	            mCamera = null;
+	            Log.e(TAG, "Failed to open native camera");
+	            return false;
+	        }
+	    }
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        synchronized (this) {
+	        if (mCamera != null) {
+	                mCamera.release();
+	                mCamera = null;
+            }
+        }
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera");
         synchronized (this) {
             if (mCamera != null && mCamera.isOpened()) {
-                Log.i(TAG, "before mCamera.getSupportedPreviewSizes()");
                 List<Size> sizes = mCamera.getSupportedPreviewSizes();
-                Log.i(TAG, "after mCamera.getSupportedPreviewSizes()");
                 int mFrameWidth = width;
                 int mFrameHeight = height;
 
@@ -54,28 +77,22 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
                 mCamera.set(Highgui.CV_CAP_PROP_FRAME_HEIGHT, mFrameHeight);
             }
         }
+
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
     }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
-        if (mCamera.isOpened()) {
         (new Thread(this)).start();
-        } else {
-            mCamera.release();
-            mCamera = null;
-            Log.e(TAG, "Failed to open native camera");
-        }
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        if (mCamera != null) {
+        releaseCamera();
-            synchronized (this) {
-                mCamera.release();
-                mCamera = null;
-            }
-        }
     }
 
     protected abstract Bitmap processFrame(VideoCapture capture);
@@ -88,8 +105,10 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
             Bitmap bmp = null;
 
             synchronized (this) {
-                if (mCamera == null)
+                if (mCamera == null) {
+                    Log.i(TAG, "mCamera == null");
                     break;
+                }
 
                 if (!mCamera.grab()) {
                     Log.e(TAG, "mCamera.grab() failed");

samples/android/tutorial-0-androidcamera/res/values/strings.xml

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <string name="app_name">Tutorial 1 Basic - 0. Android Camera</string>
+    <string name="app_name">Tutorial 0 (Basic) - Android Camera</string>
 </resources>

samples/android/tutorial-0-androidcamera/src/org/opencv/samples/tutorial0/Sample0Base.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.tutorial0;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Menu;
@@ -19,6 +21,31 @@ public class Sample0Base extends Activity {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
 	/** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {

samples/android/tutorial-0-androidcamera/src/org/opencv/samples/tutorial0/Sample0View.java

@@ -63,6 +63,7 @@ class Sample0View extends SampleViewBase {
 
 	@Override
 	protected void onPreviewStared(int previewWidth, int previewHeight) {
+		Log.i(TAG, "onPreviewStared("+previewWidth+", "+previewHeight+")");
 		/* Create a bitmap that will be used through to calculate the image to */
         mBitmap = Bitmap.createBitmap(previewWidth, previewHeight, Bitmap.Config.ARGB_8888);
     	mRGBA = new int[previewWidth * previewHeight];
@@ -70,12 +71,19 @@ class Sample0View extends SampleViewBase {
 
 	@Override
 	protected void onPreviewStopped() {
+		Log.i(TAG, "onPreviewStopped");
+		if(mBitmap != null) {
 			mBitmap.recycle();
 			mBitmap = null;
+		}
+		
+		if(mRGBA != null) {
 			mRGBA = null;
 		}
+	}
 
 	public void setViewMode(int viewMode) {
+		Log.i(TAG, "setViewMode("+viewMode+")");
 		mViewMode = viewMode;
 	}
 }

samples/android/tutorial-0-androidcamera/src/org/opencv/samples/tutorial0/SampleViewBase.java

@@ -50,8 +50,44 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
     }
 
 
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        releaseCamera();
+        mCamera = Camera.open();
+        if(mCamera == null) {
+        	Log.e(TAG, "Can't open camera!");
+        	return false;
+        }
+
+        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
+            public void onPreviewFrame(byte[] data, Camera camera) {
+                synchronized (SampleViewBase.this) {
+                    System.arraycopy(data, 0, mFrame, 0, data.length);
+                    SampleViewBase.this.notify(); 
+                }
+                camera.addCallbackBuffer(mBuffer);
+            }
+        });
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        mThreadRun = false;
+        synchronized (this) {
+	        if (mCamera != null) {
+                mCamera.stopPreview();
+                mCamera.setPreviewCallback(null);
+                mCamera.release();
+                mCamera = null;
+            }
+        }
+        onPreviewStopped();
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera");
+        synchronized (this) {
             if (mCamera != null) {
                 Camera.Parameters params = mCamera.getParameters();
                 List<Camera.Size> sizes = params.getSupportedPreviewSizes();
@@ -85,7 +121,7 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 int size = params.getPreviewSize().width * params.getPreviewSize().height;
                 size  = size * ImageFormat.getBitsPerPixel(params.getPreviewFormat()) / 8;
                 mBuffer = new byte[size];
-            /* The buffer where the current frame will be coppied */
+                /* The buffer where the current frame will be copied */
                 mFrame = new byte [size];
                 mCamera.addCallbackBuffer(mBuffer);
 
@@ -102,36 +138,21 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 mCamera.startPreview();
             }
         }
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
+    }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = Camera.open();
-
-        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
-            public void onPreviewFrame(byte[] data, Camera camera) {
-                synchronized (SampleViewBase.this) {
-                    System.arraycopy(data, 0, mFrame, 0, data.length);
-                    SampleViewBase.this.notify(); 
-                }
-                camera.addCallbackBuffer(mBuffer);
-            }
-        });
-                    
         (new Thread(this)).start();
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        mThreadRun = false;
+        releaseCamera();
-        if (mCamera != null) {
-            synchronized (this) {
-                mCamera.stopPreview();
-                mCamera.setPreviewCallback(null);
-                mCamera.release();
-                mCamera = null;
-            }
-        }
-        onPreviewStopped();
     }
 
     /* The bitmap returned by this method shall be owned by the child and released in onPreviewStopped() */
@@ -175,5 +196,6 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 }
             }
         }
+        Log.i(TAG, "Finishing processing thread");
     }
 }

samples/android/tutorial-1-addopencv/res/values/strings.xml

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <string name="app_name">Tutorial 1 Basic - 1. Add OpenCV</string>
+    <string name="app_name">Tutorial 1 (Basic) - Add OpenCV</string>
 </resources>

samples/android/tutorial-1-addopencv/src/org/opencv/samples/tutorial1/Sample1Java.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.tutorial1;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Menu;
@@ -19,6 +21,31 @@ public class Sample1Java extends Activity {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {

samples/android/tutorial-1-addopencv/src/org/opencv/samples/tutorial1/Sample1View.java

@@ -2,16 +2,15 @@ package org.opencv.samples.tutorial1;
 
 import org.opencv.android.Utils;
 import org.opencv.core.Core;
+import org.opencv.core.CvType;
 import org.opencv.core.Mat;
 import org.opencv.core.Point;
 import org.opencv.core.Scalar;
-import org.opencv.core.CvType;
 import org.opencv.imgproc.Imgproc;
 
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.util.Log;
-import android.view.SurfaceHolder;
 
 class Sample1View extends SampleViewBase {
 
@@ -94,7 +93,7 @@ class Sample1View extends SampleViewBase {
         try {
             Utils.matToBitmap(mRgba, bmp);
         } catch(Exception e) {
-            Log.e("org.opencv.samples.puzzle15", "Utils.matToBitmap() throws an exception: " + e.getMessage());
+            Log.e("org.opencv.samples.tutorial1", "Utils.matToBitmap() throws an exception: " + e.getMessage());
             bmp.recycle();
             bmp = null;
         }

samples/android/tutorial-1-addopencv/src/org/opencv/samples/tutorial1/SampleViewBase.java

@@ -49,10 +49,45 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
         	mCamera.setPreviewDisplay(null);
 	}
     
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
-        if (mCamera != null) {
+        releaseCamera();
+        mCamera = Camera.open();
+        if(mCamera == null) {
+        	Log.e(TAG, "Can't open camera!");
+        	return false;
+        }
 
+        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
+            public void onPreviewFrame(byte[] data, Camera camera) {
+                synchronized (SampleViewBase.this) {
+                    System.arraycopy(data, 0, mFrame, 0, data.length);
+                    SampleViewBase.this.notify(); 
+                }
+                camera.addCallbackBuffer(mBuffer);
+            }
+        });
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        mThreadRun = false;
+        synchronized (this) {
+	        if (mCamera != null) {
+                mCamera.stopPreview();
+                mCamera.setPreviewCallback(null);
+                mCamera.release();
+                mCamera = null;
+            }
+        }
+        onPreviewStopped();
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera");
+        synchronized (this) {
+            if (mCamera != null) {
                 Camera.Parameters params = mCamera.getParameters();
                 List<Camera.Size> sizes = params.getSupportedPreviewSizes();
                 mFrameWidth = width;
@@ -85,7 +120,7 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 int size = params.getPreviewSize().width * params.getPreviewSize().height;
                 size  = size * ImageFormat.getBitsPerPixel(params.getPreviewFormat()) / 8;
                 mBuffer = new byte[size];
-            /* The buffer where the current frame will be coppied */
+                /* The buffer where the current frame will be copied */
                 mFrame = new byte [size];
                 mCamera.addCallbackBuffer(mBuffer);
 
@@ -102,36 +137,21 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 mCamera.startPreview();
             }
         }
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
+    }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = Camera.open();
-
-        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
-            public void onPreviewFrame(byte[] data, Camera camera) {
-                synchronized (SampleViewBase.this) {
-                    System.arraycopy(data, 0, mFrame, 0, data.length);
-                    SampleViewBase.this.notify(); 
-                }
-                camera.addCallbackBuffer(mBuffer);
-            }
-        });
-                    
         (new Thread(this)).start();
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        mThreadRun = false;
+        releaseCamera();
-        if (mCamera != null) {
-            synchronized (this) {
-                mCamera.stopPreview();
-                mCamera.setPreviewCallback(null);
-                mCamera.release();
-                mCamera = null;
-            }
-        }
-        onPreviewStopped();
     }
 
     /* The bitmap returned by this method shall be owned by the child and released in onPreviewStopped() */

samples/android/tutorial-2-opencvcamera/res/values/strings.xml

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <string name="app_name">Tutorial 1 Basic - 2. Use OpenCV Camera</string>
+    <string name="app_name">Tutorial 2 (Basic) - Use OpenCV Camera</string>
 </resources>

samples/android/tutorial-2-opencvcamera/src/org/opencv/samples/tutorial2/Sample2NativeCamera.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.tutorial2;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Menu;
@@ -20,17 +22,45 @@ public class Sample2NativeCamera extends Activity {
 
     public static int           viewMode        = VIEW_MODE_RGBA;
     
+    private Sample2View 		mView;
+
     public Sample2NativeCamera() {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         Log.i(TAG, "onCreate");
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
-        setContentView(new Sample2View(this));
+        mView = new Sample2View(this);
+        setContentView(mView);
     }
 
     @Override

samples/android/tutorial-2-opencvcamera/src/org/opencv/samples/tutorial2/Sample2View.java

@@ -1,12 +1,8 @@
 package org.opencv.samples.tutorial2;
 
-import java.util.ArrayList;
-import java.util.List;
-
 import org.opencv.android.Utils;
 import org.opencv.core.Core;
 import org.opencv.core.Mat;
-import org.opencv.core.MatOfPoint;
 import org.opencv.core.Point;
 import org.opencv.core.Scalar;
 import org.opencv.highgui.Highgui;
@@ -22,36 +18,25 @@ class Sample2View extends SampleCvViewBase {
     private Mat mRgba;
     private Mat mGray;
     private Mat mIntermediateMat;
-    private Mat mIntermediateMat2;
-    private Mat mEmpty;
-    private Scalar lo, hi;
-    private Scalar bl, wh;
 
     public Sample2View(Context context) {
         super(context);
     }
 
     @Override
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public void surfaceCreated(SurfaceHolder holder) {
-        super.surfaceChanged(_holder, format, width, height);
-
         synchronized (this) {
             // initialize Mats before usage
             mGray = new Mat();
             mRgba = new Mat();
             mIntermediateMat = new Mat();
-            mIntermediateMat2 = new Mat();
-            mEmpty = new Mat();
-            lo = new Scalar(85, 100, 30);
-            hi = new Scalar(130, 255, 255);
-            bl = new Scalar(0, 0, 0, 255);
-            wh = new Scalar(255, 255, 255, 255);
         }
+        
+        super.surfaceCreated(holder);
     }
 
     @Override
     protected Bitmap processFrame(VideoCapture capture) {
-    	/**/
         switch (Sample2NativeCamera.viewMode) {
         case Sample2NativeCamera.VIEW_MODE_GRAY:
             capture.retrieve(mGray, Highgui.CV_CAP_ANDROID_GREY_FRAME);
@@ -62,36 +47,11 @@ class Sample2View extends SampleCvViewBase {
             Core.putText(mRgba, "OpenCV + Android", new Point(10, 100), 3, 2, new Scalar(255, 0, 0, 255), 3);
             break;
         case Sample2NativeCamera.VIEW_MODE_CANNY:
-            /*capture.retrieve(mGray, Highgui.CV_CAP_ANDROID_GREY_FRAME);
+            capture.retrieve(mGray, Highgui.CV_CAP_ANDROID_GREY_FRAME);
             Imgproc.Canny(mGray, mIntermediateMat, 80, 100);
             Imgproc.cvtColor(mIntermediateMat, mRgba, Imgproc.COLOR_GRAY2BGRA, 4);
-            */
-        	capture.retrieve(mRgba, Highgui.CV_CAP_ANDROID_COLOR_FRAME_RGBA);
-        	Imgproc.cvtColor(mRgba, mIntermediateMat, Imgproc.COLOR_RGB2HSV_FULL);
-        	Core.inRange(mIntermediateMat, lo, hi, mIntermediateMat2); // green
-        	Imgproc.dilate(mIntermediateMat2, mIntermediateMat2, mEmpty);
-        	//
-        	List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
-        	Mat hierarchy = new Mat();
-        	Imgproc.findContours(mIntermediateMat2, contours, hierarchy,Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);
-        	Log.d("processFrame", "contours.size()" + contours.size());
-        	double maxArea = 0;
-        	int indexMaxArea = -1;
-	       for (int i = 0; i < contours.size(); i++) {
-	    	   double s = Imgproc.contourArea(contours.get(i));
-	             if(s > maxArea){
-	    		    indexMaxArea = i;
-	    		    maxArea = s;
-	    	     }
-	       } 
-	       
-			mRgba.setTo(bl);
-			Imgproc.drawContours(mRgba, contours, indexMaxArea, wh);
-			//
-			//Imgproc.cvtColor(mIntermediateMat2, mRgba, Imgproc.COLOR_GRAY2RGBA);
 			break;
         }
-    	/**/
 
         Bitmap bmp = Bitmap.createBitmap(mRgba.cols(), mRgba.rows(), Bitmap.Config.ARGB_8888);
 
@@ -99,7 +59,7 @@ class Sample2View extends SampleCvViewBase {
         	Utils.matToBitmap(mRgba, bmp);
             return bmp;
         } catch(Exception e) {
-        	Log.e("org.opencv.samples.puzzle15", "Utils.matToBitmap() throws an exception: " + e.getMessage());
+        	Log.e("org.opencv.samples.tutorial2", "Utils.matToBitmap() throws an exception: " + e.getMessage());
             bmp.recycle();
             return null;
         }
@@ -118,9 +78,6 @@ class Sample2View extends SampleCvViewBase {
             if (mIntermediateMat != null)
                 mIntermediateMat.release();
 
-            if (mIntermediateMat2 != null)
-                mIntermediateMat2.release();
-            
             mRgba = null;
             mGray = null;
             mIntermediateMat = null;

samples/android/tutorial-2-opencvcamera/src/org/opencv/samples/tutorial2/SampleCvViewBase.java

@@ -26,13 +26,36 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        synchronized (this) {
+	        releaseCamera();
+	        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
+	        if (!mCamera.isOpened()) {
+	            mCamera.release();
+	            mCamera = null;
+	            Log.e(TAG, "Failed to open native camera");
+	            return false;
+	        }
+	    }
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        synchronized (this) {
+	        if (mCamera != null) {
+	                mCamera.release();
+	                mCamera = null;
+            }
+        }
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera");
         synchronized (this) {
             if (mCamera != null && mCamera.isOpened()) {
-                Log.i(TAG, "before mCamera.getSupportedPreviewSizes()");
                 List<Size> sizes = mCamera.getSupportedPreviewSizes();
-                Log.i(TAG, "after mCamera.getSupportedPreviewSizes()");
                 int mFrameWidth = width;
                 int mFrameHeight = height;
 
@@ -52,28 +75,22 @@ public abstract class SampleCvViewBase extends SurfaceView implements SurfaceHol
                 mCamera.set(Highgui.CV_CAP_PROP_FRAME_HEIGHT, mFrameHeight);
             }
         }
+
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
     }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
-        if (mCamera.isOpened()) {
         (new Thread(this)).start();
-        } else {
-            mCamera.release();
-            mCamera = null;
-            Log.e(TAG, "Failed to open native camera");
-        }
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        if (mCamera != null) {
+        releaseCamera();
-            synchronized (this) {
-                mCamera.release();
-                mCamera = null;
-            }
-        }
     }
 
     protected abstract Bitmap processFrame(VideoCapture capture);

samples/android/tutorial-3-native/res/values/strings.xml

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <string name="app_name">Tutorial 2 Advanced - 1. Add Native OpenCV</string>
+    <string name="app_name">Tutorial 3 (Advanced) - Add Native OpenCV</string>
 </resources>

samples/android/tutorial-3-native/src/org/opencv/samples/tutorial3/Sample3Native.java

@@ -1,23 +1,52 @@
 package org.opencv.samples.tutorial3;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Window;
 
 public class Sample3Native extends Activity {
     private static final String TAG = "Sample::Activity";
+    private Sample3View mView;
 
     public Sample3Native() {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {
         Log.i(TAG, "onCreate");
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
-        setContentView(new Sample3View(this));
+        mView = new Sample3View(this);
+        setContentView(mView);
     }
 }

samples/android/tutorial-3-native/src/org/opencv/samples/tutorial3/SampleViewBase.java

@@ -2,7 +2,6 @@ package org.opencv.samples.tutorial3;
 
 import java.io.IOException;
 import java.util.List;
-
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
@@ -49,8 +48,44 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
         	mCamera.setPreviewDisplay(null);
 	}
 
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        releaseCamera();
+        mCamera = Camera.open();
+        if(mCamera == null) {
+        	Log.e(TAG, "Can't open camera!");
+        	return false;
+        }
+
+        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
+            public void onPreviewFrame(byte[] data, Camera camera) {
+                synchronized (SampleViewBase.this) {
+                    System.arraycopy(data, 0, mFrame, 0, data.length);
+                    SampleViewBase.this.notify(); 
+                }
+                camera.addCallbackBuffer(mBuffer);
+            }
+        });
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        mThreadRun = false;
+        synchronized (this) {
+	        if (mCamera != null) {
+                mCamera.stopPreview();
+                mCamera.setPreviewCallback(null);
+                mCamera.release();
+                mCamera = null;
+            }
+        }
+        onPreviewStopped();
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera");
+        synchronized (this) {
             if (mCamera != null) {
                 Camera.Parameters params = mCamera.getParameters();
                 List<Camera.Size> sizes = params.getSupportedPreviewSizes();
@@ -84,7 +119,7 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 int size = params.getPreviewSize().width * params.getPreviewSize().height;
                 size  = size * ImageFormat.getBitsPerPixel(params.getPreviewFormat()) / 8;
                 mBuffer = new byte[size];
-            /* The buffer where the current frame will be coppied */
+                /* The buffer where the current frame will be copied */
                 mFrame = new byte [size];
                 mCamera.addCallbackBuffer(mBuffer);
 
@@ -101,38 +136,24 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 mCamera.startPreview();
             }
         }
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
+    }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = Camera.open();
-
-        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
-            public void onPreviewFrame(byte[] data, Camera camera) {
-                synchronized (SampleViewBase.this) {
-                    System.arraycopy(data, 0, mFrame, 0, data.length);
-                    SampleViewBase.this.notify(); 
-                }
-                camera.addCallbackBuffer(mBuffer);
-            }
-        });
-                    
         (new Thread(this)).start();
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        mThreadRun = false;
+        releaseCamera();
-        if (mCamera != null) {
-            synchronized (this) {
-                mCamera.stopPreview();
-                mCamera.setPreviewCallback(null);
-                mCamera.release();
-                mCamera = null;
-            }
-        }
-        onPreviewStopped();
     }
 
+
     /* The bitmap returned by this method shall be owned by the child and released in onPreviewStopped() */
     protected abstract Bitmap processFrame(byte[] data);
 

samples/android/tutorial-4-mixed/res/values/strings.xml

@@ -1,4 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <string name="app_name">Tutorial 2 Advanced - 2. Mix Java+Native OpenCV</string>
+    <string name="app_name">Tutorial 4 (Advanced) - Mix Java+Native OpenCV</string>
 </resources>

samples/android/tutorial-4-mixed/src/org/opencv/samples/tutorial4/Sample4Mixed.java

@@ -1,6 +1,8 @@
 package org.opencv.samples.tutorial4;
 
 import android.app.Activity;
+import android.app.AlertDialog;
+import android.content.DialogInterface;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.Menu;
@@ -21,6 +23,31 @@ public class Sample4Mixed extends Activity {
         Log.i(TAG, "Instantiated new " + this.getClass());
     }
 
+    @Override
+	protected void onPause() {
+        Log.i(TAG, "onPause");
+		super.onPause();
+		mView.releaseCamera();
+	}
+
+	@Override
+	protected void onResume() {
+        Log.i(TAG, "onResume");
+		super.onResume();
+		if( !mView.openCamera() ) {
+			AlertDialog ad = new AlertDialog.Builder(this).create();  
+			ad.setCancelable(false); // This blocks the 'BACK' button  
+			ad.setMessage("Fatal error: can't open camera!");  
+			ad.setButton("OK", new DialogInterface.OnClickListener() {  
+			    public void onClick(DialogInterface dialog, int which) {  
+			        dialog.dismiss();                      
+					finish();
+			    }  
+			});  
+			ad.show();
+		}
+	}
+
     /** Called when the activity is first created. */
     @Override
     public void onCreate(Bundle savedInstanceState) {

samples/android/tutorial-4-mixed/src/org/opencv/samples/tutorial4/Sample4View.java

@@ -1,14 +1,13 @@
 package org.opencv.samples.tutorial4;
 
 import org.opencv.android.Utils;
-import org.opencv.core.Mat;
 import org.opencv.core.CvType;
+import org.opencv.core.Mat;
 import org.opencv.imgproc.Imgproc;
 
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.util.Log;
-import android.view.SurfaceHolder;
 
 class Sample4View extends SampleViewBase {
 

samples/android/tutorial-4-mixed/src/org/opencv/samples/tutorial4/SampleViewBase.java

@@ -2,7 +2,6 @@ package org.opencv.samples.tutorial4;
 
 import java.io.IOException;
 import java.util.List;
-
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
@@ -49,8 +48,44 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
         	mCamera.setPreviewDisplay(null);
 	}
     
-    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+    public boolean openCamera() {
-        Log.i(TAG, "surfaceCreated");
+        Log.i(TAG, "openCamera");
+        releaseCamera();
+        mCamera = Camera.open();
+        if(mCamera == null) {
+        	Log.e(TAG, "Can't open camera!");
+        	return false;
+        }
+
+        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
+            public void onPreviewFrame(byte[] data, Camera camera) {
+                synchronized (SampleViewBase.this) {
+                    System.arraycopy(data, 0, mFrame, 0, data.length);
+                    SampleViewBase.this.notify(); 
+                }
+                camera.addCallbackBuffer(mBuffer);
+            }
+        });
+        return true;
+    }
+    
+    public void releaseCamera() {
+        Log.i(TAG, "releaseCamera");
+        mThreadRun = false;
+        synchronized (this) {
+	        if (mCamera != null) {
+                mCamera.stopPreview();
+                mCamera.setPreviewCallback(null);
+                mCamera.release();
+                mCamera = null;
+            }
+        }
+        onPreviewStopped();
+    }
+    
+    public void setupCamera(int width, int height) {
+        Log.i(TAG, "setupCamera");
+        synchronized (this) {
             if (mCamera != null) {
                 Camera.Parameters params = mCamera.getParameters();
                 List<Camera.Size> sizes = params.getSupportedPreviewSizes();
@@ -84,7 +119,7 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 int size = params.getPreviewSize().width * params.getPreviewSize().height;
                 size  = size * ImageFormat.getBitsPerPixel(params.getPreviewFormat()) / 8;
                 mBuffer = new byte[size];
-            /* The buffer where the current frame will be coppied */
+                /* The buffer where the current frame will be copied */
                 mFrame = new byte [size];
                 mCamera.addCallbackBuffer(mBuffer);
 
@@ -101,38 +136,25 @@ public abstract class SampleViewBase extends SurfaceView implements SurfaceHolde
                 mCamera.startPreview();
             }
         }
+    }
+    
+    public void surfaceChanged(SurfaceHolder _holder, int format, int width, int height) {
+        Log.i(TAG, "surfaceChanged");
+        setupCamera(width, height);
+    }
 
     public void surfaceCreated(SurfaceHolder holder) {
         Log.i(TAG, "surfaceCreated");
-        mCamera = Camera.open();
-
-        mCamera.setPreviewCallbackWithBuffer(new PreviewCallback() {
-            public void onPreviewFrame(byte[] data, Camera camera) {
-                synchronized (SampleViewBase.this) {
-                    System.arraycopy(data, 0, mFrame, 0, data.length);
-                    SampleViewBase.this.notify(); 
-                }
-                camera.addCallbackBuffer(mBuffer);
-            }
-        });
-
         (new Thread(this)).start();
     }
 
     public void surfaceDestroyed(SurfaceHolder holder) {
         Log.i(TAG, "surfaceDestroyed");
-        mThreadRun = false;
+        releaseCamera();
-        if (mCamera != null) {
-            synchronized (this) {
-                mCamera.stopPreview();
-                mCamera.setPreviewCallback(null);
-                mCamera.release();
-                mCamera = null;
-            }
-        }
-        onPreviewStopped();
     }
 
+
+
     /* The bitmap returned by this method shall be owned by the child and released in onPreviewStopped() */
     protected abstract Bitmap processFrame(byte[] data);