155 lines
4.2 KiB
Clojure
155 lines
4.2 KiB
Clojure
=?= Tutorial 2: Object Model =?=
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__________________________________________________
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[left][tutorial[001_HelloWord | Previous: Hello Word]][/left] [right][tutorial[011_ObjectConfig | Next: Object config]][/right]
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=== Objectif ===
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:** Understand ewol basic [class[ewol::Object]]
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:** Use [class[ewol::Object]] correctly
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== Basis of the Object ==
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An object in Ewol is a simple class : [class[ewol::Object]] This object is the basis of all element in the ewol system.
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This is designed to manage basis element of complexe structure:
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:** Unique ID
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:** Name
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:** Configuration (decriptive naming of parameters)
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:** Event generation and receving
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:** Xml configuration
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:** Delayed removing
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[note]
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Please do not compare with the gObject basic class...
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[/note]
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== Create an Object: ==
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In theory you can use a simple new on an object, but you need to remove the refcounting of this one by yoursef ... really awfull.
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It is really better to use the ewol::object::Shared<> declaration to auto manage it. (same as std::shared_ptr)
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[code style=c++]
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ewol::object::Shared<widget::Label> tmpObject = ewol::object::makeShared(new widget::Label());
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if (tmpObject == NULL) {
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APPL_ERROR("An error occured");
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return;
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}
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[/code]
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The object register itself on the object manager, now it will have a specific Id and no name
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Force the set of the name :
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[code style=c++]
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tmpObject->setName("my widget name");
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APPL_INFO("We just create an Object with ID=" << tmpObject->getId() << " name='" << tmpObject->getName() << "'");
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[/code]
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== Remove an Object: ==
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This is important to note that many element can have a reference on the Object.
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Then we need to use the fuction:
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[b]removeObject()[/b] to remove the Object, This will notify avery object in the system that this
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specific object has been removed.
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Then to remove an object call:
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[code style=c++]
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tmpObject->removeObject();
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[/code]
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On every object we can have an herited function: [b]virtual void onObjectRemove(const ewol::object::Shared<ewol::Object>& _removeObject);[/b]
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We need to implement this fuction to be notify an object is removed:
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[code style=c++]
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void namespeceName::ClassName::onObjectRemove(const ewol::object::Shared<ewol::Object>& _removeObject) {
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// Never forget to call upper Object (otherwise many object will keep theire reference)
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upperClass::onObjectRemove(_removeObject);
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if (_removeObject == m_object) {
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m_object.reset();
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markToRedraw(); // set only for graphical object ...
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}
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}
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[/code]
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[note]
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If you have well follow the idea, you will never declare an object in local, just use shared pointer on them.
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[/note]
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[note]
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For some case it could be interesting to see the [class[ewol::object::Owner<T>]] class that provide an automatic auto remove of object.
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See [class[ewol::widget::Container]] for an example.
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[/note]
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=== Particularity ===
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An object can remove itself, just use the function:
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[code style=c++]
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autoDestroy();
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[/code]
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== Retrieve an Object: ==
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In Ewol this is possible to get a object with his name.
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This is really simple.
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=== In an Object ===
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Call a simple function define in the Object:
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[code style=c++]
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#include <ewol/object/Manager.h>
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...
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ewol::object::Shared<ewol::Object> tmpObject = getObjectManager().get("name of the object");
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if (tmpObject == NULL) {
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APPL_ERROR("The Object does not exist");
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}
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[/code]
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=== Not in an Object ===
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In this case, we need to get the context manager and after the object manager:
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[code style=c++]
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#include <ewol/object/Manager.h>
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#include <ewol/context/Context.h>
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...
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ewol::object::Shared<ewol::Object> tmpObject = ewol::getContext().getObjectManager().get("name of the object");
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if (tmpObject == NULL) {
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APPL_ERROR("The Object does not exist");
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}
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[/code]
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=== Casting your object ===
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It could be really interesting to retrive your own instance:
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[code style=c++]
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ewol::object::Shared<ewol::Object> tmpObject ...;
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ewol::object::Shared<appl::MyOwnObject> myObject = ewol::dynamic_pointer_cast<appl::MyOwnObject>(tmpObject);
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[/code]
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== conclusion ==
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If you follow these rules, you will not have memory leek and no segmentation fault on the ewol system.
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[note]
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To be sure that the name is unique, just add the current creator object Id in the name.
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See [class[ewol::widget::FileChooser]] class for an example.
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[/note]
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