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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 \example itemviews/spinboxdelegate |
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44 \title Spin Box Delegate Example |
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45 |
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46 The Spin Box Delegate example shows how to create an editor for a custom delegate in |
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47 the model/view framework by reusing a standard Qt editor widget. |
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48 |
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49 The model/view framework provides a standard delegate that is used by default |
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50 with the standard view classes. For most purposes, the selection of editor |
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51 widgets available through this delegate is sufficient for editing text, boolean |
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52 values, and other simple data types. However, for specific data types, it is |
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53 sometimes necessary to use a custom delegate to either display the data in a |
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54 specific way, or allow the user to edit it with a custom control. |
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55 |
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56 \image spinboxdelegate-example.png |
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57 |
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58 This concepts behind this example are covered in the |
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59 \l{model-view-delegate.html}{Delegate Classes} chapter of the |
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60 \l{model-view-programming.html}{Model/View Programming} overview. |
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61 |
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62 \section1 SpinBoxDelegate Class Definition |
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63 |
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64 The definition of the delegate is as follows: |
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65 |
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66 \snippet examples/itemviews/spinboxdelegate/delegate.h 0 |
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67 |
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68 The delegate class declares only those functions that are needed to |
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69 create an editor widget, display it at the correct location in a view, |
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70 and communicate with a model. Custom delegates can also provide their |
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71 own painting code by reimplementing the \c paintEvent() function. |
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72 |
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73 \section1 SpinBoxDelegate Class Implementation |
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74 |
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75 Since the delegate is stateless, the constructor only needs to |
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76 call the base class's constructor with the parent QObject as its |
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77 argument: |
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78 |
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79 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 0 |
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80 |
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81 Since the delegate is a subclass of QItemDelegate, the data it retrieves |
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82 from the model is displayed in a default style, and we do not need to |
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83 provide a custom \c paintEvent(). |
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84 |
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85 The \c createEditor() function returns an editor widget, in this case a |
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86 spin box that restricts values from the model to integers from 0 to 100 |
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87 inclusive. |
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88 |
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89 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 1 |
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90 |
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91 We install an event filter on the spin box to ensure that it behaves in |
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92 a way that is consistent with other delegates. The implementation for |
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93 the event filter is provided by the base class. |
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94 |
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95 The \c setEditorData() function reads data from the model, converts it |
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96 to an integer value, and writes it to the editor widget. |
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97 |
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98 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 2 |
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99 |
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100 Since the view treats delegates as ordinary QWidget instances, we have |
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101 to use a static cast before we can set the value in the spin box. |
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102 |
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103 The \c setModelData() function reads the contents of the spin box, and |
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104 writes it to the model. |
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105 |
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106 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 3 |
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107 |
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108 We call \l{QSpinBox::interpretText()}{interpretText()} to make sure that |
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109 we obtain the most up-to-date value in the spin box. |
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110 |
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111 The \c updateEditorGeometry() function updates the editor widget's |
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112 geometry using the information supplied in the style option. This is the |
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113 minimum that the delegate must do in this case. |
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114 |
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115 \snippet examples/itemviews/spinboxdelegate/delegate.cpp 4 |
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116 |
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117 More complex editor widgets may divide the rectangle available in |
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118 \c{option.rect} between different child widgets if required. |
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119 |
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120 \section1 The Main Function |
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121 |
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122 This example is written in a slightly different way to many of the |
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123 other examples supplied with Qt. To demonstrate the use of a custom |
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124 editor widget in a standard view, it is necessary to set up a model |
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125 containing some arbitrary data and a view to display it. |
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126 |
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127 We set up the application in the normal way, construct a standard item |
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128 model to hold some data, set up a table view to use the data in the |
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129 model, and construct a custom delegate to use for editing: |
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130 |
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131 \snippet examples/itemviews/spinboxdelegate/main.cpp 0 |
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132 |
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133 The table view is informed about the delegate, and will use it to |
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134 display each of the items. Since the delegate is a subclass of |
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135 QItemDelegate, each cell in the table will be rendered using standard |
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136 painting operations. |
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137 |
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138 We insert some arbitrary data into the model for demonstration purposes: |
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139 |
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140 \snippet examples/itemviews/spinboxdelegate/main.cpp 1 |
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141 \snippet examples/itemviews/spinboxdelegate/main.cpp 2 |
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142 |
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143 Finally, the table view is displayed with a window title, and we start |
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144 the application's event loop: |
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145 |
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146 \snippet examples/itemviews/spinboxdelegate/main.cpp 3 |
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147 |
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148 Each of the cells in the table can now be edited in the usual way, but |
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149 the spin box ensures that the data returned to the model is always |
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150 constrained by the values allowed by the spin box delegate. |
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151 */ |