| 1 | /****************************************************************************
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| 2 | **
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| 3 | ** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
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| 4 | ** All rights reserved.
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| 5 | ** Contact: Nokia Corporation ([email protected])
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| 6 | **
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| 7 | ** This file is part of the documentation of the Qt Toolkit.
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| 8 | **
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| 9 | ** $QT_BEGIN_LICENSE:FDL$
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| 10 | ** Commercial Usage
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| 11 | ** Licensees holding valid Qt Commercial licenses may use this file in
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| 12 | ** accordance with the Qt Commercial License Agreement provided with the
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| 13 | ** Software or, alternatively, in accordance with the terms contained in a
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| 14 | ** written agreement between you and Nokia.
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| 15 | **
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| 16 | ** GNU Free Documentation License
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| 17 | ** Alternatively, this file may be used under the terms of the GNU Free
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| 18 | ** Documentation License version 1.3 as published by the Free Software
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| 19 | ** Foundation and appearing in the file included in the packaging of this
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| 20 | ** file.
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| 21 | **
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| 22 | ** If you have questions regarding the use of this file, please contact
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| 23 | ** Nokia at [email protected].
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| 24 | ** $QT_END_LICENSE$
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| 25 | **
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| 26 | ****************************************************************************/
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| 27 |
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| 28 | /*!
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| 29 | \example gestures/imagegestures
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| 30 | \title Image Gestures Example
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| 31 |
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| 32 | This example shows how to enable gestures for a widget and use gesture input
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| 33 | to perform actions.
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| 34 |
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| 35 | We use two classes to create the user interface for the application: \c MainWidget
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| 36 | and \c ImageWidget. The \c MainWidget class is simply used as a container for the
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| 37 | \c ImageWidget class, which we will configure to accept gesture input. Since we
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| 38 | are interested in the way gestures are used, we will concentrate on the
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| 39 | implementation of the \c ImageWidget class.
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| 40 |
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| 41 | \section1 ImageWidget Class Definition
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| 42 |
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| 43 | The \c ImageWidget class is a simple QWidget subclass that reimplements the general
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| 44 | QWidget::event() handler function in addition to several more specific event handlers:
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| 45 |
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| 46 | \snippet examples/gestures/imagegestures/imagewidget.h class definition begin
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| 47 | \dots
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| 48 | \snippet examples/gestures/imagegestures/imagewidget.h class definition end
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| 49 |
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| 50 | We also implement a private helper function, \c gestureEvent(), to help manage
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| 51 | gesture events delivered to the widget, and three functions to perform actions
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| 52 | based on gestures: \c panTriggered(), \c pinchTriggered() and \c swipeTriggered().
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| 53 |
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| 54 | \section1 ImageWidget Class Implementation
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| 55 |
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| 56 | In the widget's constructor, we begin by setting up various parameters that will
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| 57 | be used to control the way images are displayed.
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| 58 |
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| 59 | \snippet examples/gestures/imagegestures/imagewidget.cpp constructor
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| 60 |
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| 61 | We enable three of the standard gestures for the widget by calling QWidget::grabGesture()
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| 62 | with the types of gesture we need. These will be recognized by the application's
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| 63 | default gesture recognizer, and events will be delivered to our widget.
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| 64 |
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| 65 | Since QWidget does not define a specific event handler for gestures, the widget
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| 66 | needs to reimplement the general QWidget::event() to receive gesture events.
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| 67 |
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| 68 | \snippet examples/gestures/imagegestures/imagewidget.cpp event handler
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| 69 |
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| 70 | We implement the event handler to delegate gesture events to a private function
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| 71 | specifically written for the task, and pass all other events to QWidget's
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| 72 | implementation.
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| 73 |
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| 74 | The \c gestureHandler() function examines the gestures supplied by the
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| 75 | newly-delivered QGestureEvent. Since only one gesture of a given type can be
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| 76 | used on a widget at any particular time, we can check for each gesture type
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| 77 | using the QGestureEvent::gesture() function:
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| 78 |
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| 79 | \snippet examples/gestures/imagegestures/imagewidget.cpp gesture event handler
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| 80 |
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| 81 | If a QGesture object is supplied for a certain type of gesture, we call a special
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| 82 | purpose function to deal with it, casting the gesture object to the appropriate
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| 83 | QGesture subclass.
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| 84 |
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| 85 | To illustrate how a standard gesture can be interpreted by an application, we
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| 86 | show the implementation of the \c swipeTriggered() function, which handles the
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| 87 | gesture associated with a brushing or swiping motion on the user's display or
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| 88 | input device:
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| 89 |
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| 90 | \snippet examples/gestures/imagegestures/imagewidget.cpp swipe function
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| 91 |
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| 92 | The QSwipeGesture class provides specialized functions and defines a enum
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| 93 | to make it more convenient for developers to discover which direction, if
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| 94 | any, the user swiped the display. Here, we simply navigate to the previous
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| 95 | image in the collection if the user swiped upwards or to the left; otherwise
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| 96 | we navigate to the next image in the collection.
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| 97 |
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| 98 | The other gestures are also handled by special purpose functions, but use
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| 99 | the values of properties held by the QGesture object passed to them.
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| 100 | */
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