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2 ** |
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3 ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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38 ** $QT_END_LICENSE$ |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \page gestures-overview.html |
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44 \title Gestures Programming |
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45 \ingroup frameworks-technologies |
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46 \startpage index.html Qt Reference Documentation |
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47 |
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48 \brief An overview of the Qt support for Gesture programming. |
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49 |
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50 Qt includes a framework for gesture programming that gives has the ability |
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51 to form gestures from a series of events, independently of the input methods |
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52 used. A gesture could be a particular movement of a mouse, a touch screen |
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53 action, or a series of events from some other source. The nature of the input, |
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54 the interpretation of the gesture and the action taken are the choice of the |
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55 developer. |
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56 |
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57 \tableofcontents |
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58 |
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59 \section1 Overview |
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60 |
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61 QGesture is the central class in Qt's gesture framework, providing a container |
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62 for information about gestures performed by the user. QGesture exposes |
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63 properties that give general information that is common to all gestures, and |
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64 these can be extended to provide additional gesture-specific information. |
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65 Common panning, pinching and swiping gestures are represented by specialized |
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66 classes: QPanGesture, QPinchGesture and QSwipeGesture. |
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67 |
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68 Developers can also implement new gestures by subclassing and extending the |
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69 QGestureRecognizer class. Adding support for a new gesture involves implementing |
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70 code to recognize the gesture from input events. This is described in the |
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71 \l{Creating Your Own Gesture Recognizer} section. |
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72 |
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73 \section1 Using Standard Gestures with Widgets |
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74 |
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75 Gestures can be enabled for instances of QWidget and QGraphicsObject subclasses. |
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76 An object that accepts gesture input is referred to as a \e{target object}. |
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77 |
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78 To enable a gesture for a target object, call its QWidget::grabGesture() or |
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79 QGraphicsObject::grabGesture() function with an argument describing the |
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80 required gesture type. The standard types are defined by the Qt::GestureType |
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81 enum and include many commonly used gestures. |
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82 |
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83 \snippet examples/gestures/imagegestures/imagewidget.cpp enable gestures |
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84 |
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85 In the above code, the gesture is set up in the constructor of the target object |
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86 itself. |
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87 |
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88 When the user performs a gesture, QGestureEvent events will be delivered to the |
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89 target object, and these can be handled by reimplementing the QWidget::event() |
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90 handler function for widgets or QGraphicsItem::sceneEvent() for graphics objects. |
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91 |
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92 For convenience, the \l{Image Gestures Example} reimplements the general |
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93 \l{QWidget::}{event()} handler function and delegates gesture events to a |
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94 specialized gestureEvent() function: |
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95 |
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96 \snippet examples/gestures/imagegestures/imagewidget.cpp event handler |
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97 |
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98 The gesture events delivered to the target object can be examined individually |
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99 and dealt with appropriately: |
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100 |
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101 \snippet examples/gestures/imagegestures/imagewidget.cpp gesture event handler |
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102 |
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103 Responding to a gesture is simply a matter of obtaining the QGesture object |
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104 delivered in the QGestureEvent sent to the target object and examining the |
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105 information it contains. |
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106 |
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107 \snippet examples/gestures/imagegestures/imagewidget.cpp swipe function |
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108 |
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109 Here, we examine the direction in which the user swiped the widget and modify |
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110 its contents accordingly. |
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111 |
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112 |
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113 \section1 Creating Your Own Gesture Recognizer |
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114 |
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115 Adding support for a new gesture involves creating and registering a new gesture |
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116 recognizer. Depending on the recognition process for the gesture, it may also |
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117 involve creating a new gesture object. |
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118 |
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119 To create a new recognizer, you need to subclass QGestureRecognizer to create a |
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120 custom recognizer class. There is one virtual function that you must reimplement |
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121 and two others that can be reimplemented as required. |
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122 |
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123 \section2 Filtering Input Events |
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124 |
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125 The \l{QGestureRecognizer::}{recognize()} function must be reimplemented. |
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126 This function handles and filters the incoming input events for the target objects |
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127 and determines whether or not they correspond to the gesture the recognizer is |
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128 looking for. |
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129 |
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130 Although the logic for gesture recognition is implemented in this function, |
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131 possibly using a state machine based on the Qt::GestureState enums, you can store |
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132 persistent information about the state of the recognition process in the QGesture |
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133 object supplied. |
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134 |
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135 Your \l{QGestureRecognizer::}{recognize()} function must return a value of |
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136 QGestureRecognizer::Result that indicates the state of recognition for a given gesture and |
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137 target object. This determines whether or not a gesture event will be delivered |
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138 to a target object. |
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139 |
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140 \section2 Custom Gestures |
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141 |
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142 If you choose to represent a gesture by a custom QGesture subclass, you will need to |
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143 reimplement the \l{QGestureRecognizer::}{create()} function to construct |
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144 instances of your gesture class instead of standard QGesture instances. Alternatively, |
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145 you may want to use standard QGesture instances, but add additional dynamic properties |
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146 to them to express specific details of the gesture you want to handle. |
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147 |
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148 \section2 Resetting Gestures |
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149 |
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150 If you use custom gesture objects that need to be reset or otherwise specially |
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151 handled when a gesture is canceled, you need to reimplement the |
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152 \l{QGestureRecognizer::}{reset()} function to perform these special tasks. |
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153 |
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154 Note that QGesture objects are only created once for each combination of target object |
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155 and gesture type, and they might be reused every time the user attempts to perform the |
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156 same gesture type on the target object. As a result, it can be useful to reimplement |
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157 the \l{QGestureRecognizer::}{reset()} function to clean up after each previous attempt |
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158 at recognizing a gesture. |
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159 |
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160 |
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161 \section1 Using a New Gesture Recognizer |
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162 |
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163 To use a gesture recognizer, construct an instance of your QGestureRecognizer |
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164 subclass, and register it with the application with |
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165 QGestureRecognizer::registerRecognizer(). A recognizer for a given type of |
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166 gesture can be removed with QGestureRecognizer::unregisterRecognizer(). |
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167 |
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168 |
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169 \section1 Further Reading |
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170 |
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171 The \l{gestures/imagegestures}{Image Gestures Example} shows how to enable |
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172 gestures for a widget in a simple image viewer application. |
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173 */ |