101 lines
4.7 KiB
Plaintext
101 lines
4.7 KiB
Plaintext
/****************************************************************************
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**
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** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
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** Contact: http://www.qt-project.org/legal
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**
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** This file is part of the documentation of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:FDL$
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** Commercial License Usage
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** Licensees holding valid commercial Qt licenses may use this file in
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** accordance with the commercial license agreement provided with the
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** Software or, alternatively, in accordance with the terms contained in
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** a written agreement between you and Digia. For licensing terms and
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** conditions see http://qt.digia.com/licensing. For further information
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** use the contact form at http://qt.digia.com/contact-us.
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**
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** GNU Free Documentation License Usage
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** Alternatively, this file may be used under the terms of the GNU Free
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** Documentation License version 1.3 as published by the Free Software
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** Foundation and appearing in the file included in the packaging of
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** this file. Please review the following information to ensure
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** the GNU Free Documentation License version 1.3 requirements
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** will be met: http://www.gnu.org/copyleft/fdl.html.
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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/*!
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\example gestures/imagegestures
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\title Image Gestures Example
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This example shows how to enable gestures for a widget and use gesture input
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to perform actions.
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We use two classes to create the user interface for the application: \c MainWidget
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and \c ImageWidget. The \c MainWidget class is simply used as a container for the
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\c ImageWidget class, which we will configure to accept gesture input. Since we
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are interested in the way gestures are used, we will concentrate on the
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implementation of the \c ImageWidget class.
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\section1 ImageWidget Class Definition
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The \c ImageWidget class is a simple QWidget subclass that reimplements the general
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QWidget::event() handler function in addition to several more specific event handlers:
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\snippet examples/gestures/imagegestures/imagewidget.h class definition begin
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\dots
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\snippet examples/gestures/imagegestures/imagewidget.h class definition end
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We also implement a private helper function, \c gestureEvent(), to help manage
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gesture events delivered to the widget, and three functions to perform actions
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based on gestures: \c panTriggered(), \c pinchTriggered() and \c swipeTriggered().
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\section1 ImageWidget Class Implementation
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In the widget's constructor, we begin by setting up various parameters that will
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be used to control the way images are displayed.
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\snippet examples/gestures/imagegestures/imagewidget.cpp constructor
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We enable three of the standard gestures for the widget by calling QWidget::grabGesture()
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with the types of gesture we need. These will be recognized by the application's
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default gesture recognizer, and events will be delivered to our widget.
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Since QWidget does not define a specific event handler for gestures, the widget
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needs to reimplement the general QWidget::event() to receive gesture events.
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\snippet examples/gestures/imagegestures/imagewidget.cpp event handler
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We implement the event handler to delegate gesture events to a private function
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specifically written for the task, and pass all other events to QWidget's
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implementation.
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The \c gestureHandler() function examines the gestures supplied by the
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newly-delivered QGestureEvent. Since only one gesture of a given type can be
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used on a widget at any particular time, we can check for each gesture type
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using the QGestureEvent::gesture() function:
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\snippet examples/gestures/imagegestures/imagewidget.cpp gesture event handler
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If a QGesture object is supplied for a certain type of gesture, we call a special
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purpose function to deal with it, casting the gesture object to the appropriate
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QGesture subclass.
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To illustrate how a standard gesture can be interpreted by an application, we
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show the implementation of the \c swipeTriggered() function, which handles the
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gesture associated with a brushing or swiping motion on the user's display or
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input device:
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\snippet examples/gestures/imagegestures/imagewidget.cpp swipe function
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The QSwipeGesture class provides specialized functions and defines a enum
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to make it more convenient for developers to discover which direction, if
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any, the user swiped the display. Here, we simply navigate to the previous
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image in the collection if the user swiped upwards or to the left; otherwise
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we navigate to the next image in the collection.
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The other gestures are also handled by special purpose functions, but use
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the values of properties held by the QGesture object passed to them.
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*/
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