New in version 4.6.
Gesture recognizers are responsible for creating and managing
QGestureobjects and monitoring input events sent to
QGestureRecognizeris the base class for implementing custom gestures.
Developers that only need to provide gesture recognition for standard gestures do not need to use this class directly. Instances will be created behind the scenes by the framework.
For an overview of gesture handling in Qt and information on using gestures in your applications, see the Gestures in Widgets and Graphics View document.
The process of recognizing gestures involves filtering input events sent to specific objects, and modifying the associated
QGestureobjects to include relevant information about the user’s input.
Gestures are created when the framework calls
create()to handle user input for a particular instance of a
QGestureobject is created for each widget or item that is configured to use gestures.
Supporting New Gestures¶
To add support for new gestures, you need to derive from
QGestureRecognizerto create a custom recognizer class, construct an instance of this class, and register it with the application by calling
registerRecognizer(). You can also subclass
QGestureto create a custom gesture class, or rely on dynamic properties to express specific details of the gesture you want to handle.
QGestureRecognizersubclass needs to reimplement the
recognize()function to handle and filter the incoming input events for
QGraphicsObjectsubclasses. Although the logic for gesture recognition is implemented in this function, you can store persistent information about the state of the recognition process in the
QGestureobject supplied. The
recognize()function must return a value of
Resultthat indicates the state of recognition for a given gesture and target object. This determines whether or not a gesture event will be delivered to a target object.
If you choose to represent a gesture by a custom
QGesturesubclass, you will need to reimplement the
create()function to construct instances of your gesture class. Similarly, you may need to reimplement the
reset()function if your custom gesture objects need to be specially handled when a gesture is canceled.
Constructs a new gesture recognizer object.
This enum describes the result of the current event filtering step in a gesture recognizer state machine.
The result consists of a state value (one of Ignore, , , , ) and an optional hint ().
The event does not change the state of the recognizer.
The event changed the internal state of the recognizer, but it isn’t clear yet if it is a gesture or not. The recognizer needs to filter more events to decide. Gesture recognizers in the state may be reset automatically if they take too long to recognize gestures.
The event made it clear that it is not a gesture. If the gesture recognizer was in GestureTriggered state before, then the gesture is canceled and the appropriate
QGestureobject will be delivered to the target as a part of a
This hint specifies that the gesture framework should consume the filtered event and not deliver it to the receiver.
- Return type
Reimplement this function to create a custom
QGesture-derived gesture object if necessary.
The application takes ownership of the created gesture object.
recognize(state, watched, event)¶
- Return type
Handles the given
watchedobject, updating the state of the
gestureobject as required, and returns a suitable result for the current recognition step.
The result reflects how much of the gesture has been recognized. The state of the
gestureobject is set depending on the result.
- Return type
Registers the given
recognizerin the gesture framework and returns a gesture ID for it.
The application takes ownership of the
recognizerand returns the gesture type ID associated with it. For gesture recognizers which handle custom
QGestureobjects (i.e., those which return
gestureType()function) the return value is a generated gesture ID with the
This function is called by the framework to reset a given
Reimplement this function to implement additional requirements for custom
QGestureobjects. This may be necessary if you implement a custom
QGesturewhose properties need special handling when the gesture is reset.
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