CopperSpice API  1.9.1
QGestureRecognizer Class Referenceabstract

The QGestureRecognizer class provides the infrastructure for gesture recognition. More...

Inherited by QFlickGestureRecognizer

Public Typedefs

using Result = QFlags< ResultFlag >

Public Types

enum  ResultFlag

Public Methods

 QGestureRecognizer ()
virtual ~QGestureRecognizer ()
virtual QGesturecreate (QObject *target)
virtual Result recognize (QGesture *gesture, QObject *watched, QEvent *event) = 0
virtual void reset (QGesture *gesture)

Static Public Methods

static Qt::GestureType registerRecognizer (QGestureRecognizer *recognizer)
static void unregisterRecognizer (Qt::GestureType type)

Detailed Description

The QGestureRecognizer class provides the infrastructure for gesture recognition.

Gesture recognizers are responsible for creating and managing QGesture objects and monitoring input events sent to QWidget and QGraphicsObject subclasses. QGestureRecognizer is 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 automatically be created.

For an overview of gesture handling in CopperSpice and information on using gestures in your applications, refer to Gestures Programming.

Recognizing Gestures

The process of recognizing gestures involves filtering input events sent to specific objects, and modifying the associated QGesture objects to include relevant information about the user's input.

Gestures are created by calling create() to handle user input for a particular instance of a QWidget or QGraphicsObject subclass. A QGesture object is created for each widget or item that is configured to use gestures.

Once a QGesture has been created for a target object, the gesture recognizer will receive events for it in its recognize() handler function.

When a gesture is canceled, the reset() function is called, giving the recognizer the chance to update the appropriate properties in the corresponding QGesture object.

Supporting New Gestures

To add support for new gestures, you need to derive from QGestureRecognizer to create a custom recognizer class, construct an instance of this class, and register it with the application by calling QGestureRecognizer::registerRecognizer(). You can also subclass QGesture to create a custom gesture class, or rely on dynamic properties to express specific details of the gesture you want to handle.

Your custom QGestureRecognizer subclass needs to reimplement the recognize() function to handle and filter the incoming input events for QWidget and QGraphicsObject subclasses. 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 QGesture object supplied. The recognize() function must return a value of QGestureRecognizer::Result that 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 QGesture subclass, 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.

See also

Member Typedef Documentation

Member Enumeration Documentation

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, MayBeGesture, TriggerGesture, FinishGesture, CancelGesture) and an optional hint (ConsumeEventHint).

QGestureRecognizer::Ignore0x0001 The event does not change the state of the recognizer.
QGestureRecognizer::MayBeGesture0x0002 The event changed the internal state of the recognizer, but it is not clear yet if it is a gesture or not. The recognizer needs to filter more events to decide. Gesture recognizers in the MayBeGesture state may be reset automatically if they take too long to recognize gestures.
QGestureRecognizer::TriggerGesture0x0004 The gesture has been triggered and the appropriate QGesture object will be delivered to the target as a part of a QGestureEvent.
QGestureRecognizer::FinishGesture0x0008 The gesture has been finished successfully and the appropriate QGesture object will be delivered to the target as a part of a QGestureEvent.
QGestureRecognizer::CancelGesture0x0010 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 QGesture object will be delivered to the target as a part of a QGestureEvent.
QGestureRecognizer::ConsumeEventHint0x0100This hint specifies that the gesture should consume the filtered event and not deliver it to the receiver.
See also

Constructor & Destructor Documentation

QGestureRecognizer::QGestureRecognizer ( )

Constructs a new gesture recognizer object.

QGestureRecognizer::~QGestureRecognizer ( )

Destroys the gesture recognizer.

Method Documentation

QGesture * QGestureRecognizer::create ( QObject target)

This function is called by CopperSpice to create a new QGesture object for the given target (QWidget or QGraphicsObject).

Reimplement this function to create a custom QGesture-derived gesture object if necessary.

The application takes ownership of the created gesture object.

Result QGestureRecognizer::recognize ( QGesture gesture,
QObject watched,
QEvent event 
pure virtual

Handles the given event for the watched object, updating the state of the gesture object as required, and returns a suitable result for the current recognition step.

This function is called to allow the recognizer to filter input events dispatched to QWidget or QGraphicsObject instances that it is monitoring.

The result reflects how much of the gesture has been recognized. The state of the gesture object is set depending on the result.

See also
Qt::GestureType QGestureRecognizer::registerRecognizer ( QGestureRecognizer *  recognizer)

Registers the given recognizer and returns a gesture ID for it.

The application takes ownership of the recognizer and returns the gesture type ID associated with it. For gesture recognizers which handle custom QGesture objects (i.e., those which return Qt::CustomGesture in a QGesture::gestureType() function) the return value is a generated gesture ID with the Qt::CustomGesture flag set.

See also
unregisterRecognizer(), QGestureRecognizer::create(), QGesture
void QGestureRecognizer::reset ( QGesture gesture)

This function is called to reset a given gesture.

Reimplement this function to implement additional requirements for custom QGesture objects. This may be necessary if you implement a custom QGesture whose properties need special handling when the gesture is reset.

void QGestureRecognizer::unregisterRecognizer ( Qt::GestureType  type)

Unregisters all gesture recognizers of the specified type.

See also