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1 /**************************************************************************** |
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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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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \example graphicsview/basicgraphicslayouts |
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44 \title Basic Graphics Layouts Example |
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45 |
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46 The Basic Graphics Layouts example shows how to use the layout classes |
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47 in QGraphicsView: QGraphicsLinearLayout and QGraphicsGridLayout. |
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48 In addition to that it shows how to write your own custom layout item. |
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49 |
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50 \image basicgraphicslayouts-example.png Screenshot of the Basic Layouts Example |
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51 |
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52 \section1 Window Class Definition |
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53 |
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54 The \c Window class is a subclass of QGraphicsWidget. It has a |
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55 constructor with a QGraphicsWidget \a parent as its parameter. |
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56 |
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57 \snippet examples/graphicsview/basicgraphicslayouts/window.h 0 |
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58 |
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59 \section1 Window Class Implementation |
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60 |
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61 The constructor of \c Window instantiates a QGraphicsLinearLayout object, |
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62 \c windowLayout, with vertical orientation. We instantiate another |
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63 QGraphicsLinearLayout object, \c linear, whose parent is \c windowLayout. |
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64 Next, we create a \c LayoutItem object, \c item and add it to \c linear |
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65 with the \l{QGraphicsLinearLayout::}{addItem()} function. We also provide |
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66 \c item with a \l{QGraphicsLinearLayout::setStretchFactor()} |
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67 {stretchFactor}. |
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68 |
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69 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 0 |
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70 |
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71 We repeat the process: |
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72 |
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73 \list |
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74 \o create a new \c LayoutItem, |
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75 \o add the item \c linear, and |
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76 \o provide a stretch factor. |
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77 \endlist |
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78 |
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79 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 1 |
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80 |
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81 We then add \c linear to \c windowLayout, nesting two |
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82 QGraphicsLinearLayout objects. Apart from the QGraphicsLinearLayout, we |
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83 also use a QGraphicsGridLayout object, \c grid, which is a 4x3 grid with |
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84 some cells spanning to other rows. |
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85 |
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86 We create seven \c LayoutItem objects and place them into \c grid with |
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87 the \l{QGraphicsGridLayout::}{addItem()} function as shown in the code |
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88 snippet below: |
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89 |
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90 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 2 |
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91 |
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92 The first item we add to \c grid is placed in the top left cell, |
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93 spanning four rows. The next two items are placed in the second column, |
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94 and they span two rows. Each item's \l{QGraphicsWidget::}{maximumHeight()} |
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95 and \l{QGraphicsWidget::}{minimumHeight()} are set to be equal so that |
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96 they do not expand vertically. As a result, these items will not |
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97 fit vertically in their cells. So, we specify that they should be |
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98 vertically aligned in the center of the cell using Qt::AlignVCenter. |
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99 |
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100 Finally, \c grid itself is added to \c windowLayout. Unlike |
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101 QGridLayout::addItem(), QGraphicsGridLayout::addItem() requires a row |
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102 and a column for its argument, specifying which cell the item should be |
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103 positioned in. Also, if the \c rowSpan and \c columnSpan arguments |
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104 are omitted, they will default to 1. |
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105 |
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106 Note that we do not specify a parent for each \c LayoutItem that we |
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107 construct, as all these items will be added to \c windowLayout. When we |
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108 add an item to a layout, it will be automatically reparented to the widget |
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109 on which the layout is installed. |
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110 |
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111 \snippet examples/graphicsview/basicgraphicslayouts/window.cpp 3 |
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112 |
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113 Now that we have set up \c grid and added it to \c windowLayout, we |
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114 install \c windowLayout onto the window object using |
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115 QGraphicsWidget::setLayout() and we set the window title. |
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116 |
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117 \section1 LayoutItem Class Definition |
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118 |
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119 The \c LayoutItem class is a subclass of QGraphicsLayoutItem and |
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120 QGraphicsItem. It has a constructor, a destructor, and some required |
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121 reimplementations. |
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122 Since it inherits QGraphicsLayoutItem it must reimplement |
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123 {QGraphicsLayoutItem::setGeometry()}{setGeometry()} and |
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124 {QGraphicsLayoutItem::sizeHint()}{sizeHint()}. |
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125 In addition to that it inherits QGraphicsItem, so it must reimplement |
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126 {QGraphicsItem::boundingRect()}{boundingRect()} and |
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127 {QGraphicsItem::paint()}{paint()}. |
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128 |
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129 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.h 0 |
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130 |
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131 The \c LayoutItem class also has a private instance of QPixmap, \c m_pix. |
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132 |
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133 \section1 LayoutItem Class Implementation |
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134 |
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135 In \c{LayoutItem}'s constructor, \c m_pix is instantiated and the |
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136 \c{block.png} image is loaded into it. |
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137 |
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138 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 0 |
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139 |
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140 We use the Q_UNUSED() macro to prevent the compiler from generating |
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141 warnings regarding unused parameters. |
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142 |
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143 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 1 |
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144 |
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145 The idea behind the \c paint() function is to paint the |
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146 background rect then paint a rect around the pixmap. |
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147 |
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148 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 2 |
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149 |
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150 The reimplementation of {QGraphicsItem::boundingRect()}{boundingRect()} |
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151 will set the top left corner at (0,0), and the size of it will be |
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152 the size of the layout items |
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153 {QGraphicsLayoutItem::geometry()}{geometry()}. This is the area that |
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154 we paint within. |
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155 |
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156 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 3 |
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157 |
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158 |
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159 The reimplementation of {QGraphicsLayoutItem::setGeometry()}{setGeometry()} |
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160 simply calls its baseclass implementation. However, since this will change |
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161 the boundingRect we must also call |
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162 {QGraphicsItem::prepareGeometryChange()}{prepareGeometryChange()}. |
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163 Finally, we move the item according to \c geom.topLeft(). |
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164 |
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165 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 4 |
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166 |
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167 |
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168 Since we don't want the size of the item to be smaller than the pixmap, we |
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169 must make sure that we return a size hint that is larger than \c m_pix. |
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170 We also add some extra space around for borders that we will paint later. |
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171 Alternatively, you could scale the pixmap to prevent the item from |
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172 becoming smaller than the pixmap. |
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173 The preferred size is the same as the minimum size hint, while we set |
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174 maximum to be a large value |
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175 |
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176 \snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 5 |
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177 |
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178 */ |