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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 \example layouts/flowlayout |
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44 \title Flow Layout Example |
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45 |
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46 The Flow Layout example demonstrates a custom layout that arranges child |
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47 widgets from left to right and top to bottom in a top-level widget. |
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48 |
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49 \image flowlayout-example.png Screenshot of the Flow Layout example |
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50 |
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51 The items are first laid out horizontally and then vertically when each line |
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52 in the layout runs out of space. |
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53 |
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54 The Flowlayout class mainly uses QLayout and QWidgetItem, while the |
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55 Window uses QWidget and QLabel. We will only document the definition |
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56 and implementation of \c FlowLayout below. |
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57 |
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58 \section1 FlowLayout Class Definition |
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59 |
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60 The \c FlowLayout class inherits QLayout. It is a custom layout class |
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61 that arranges its child widgets horizontally and vertically. |
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62 |
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63 \snippet examples/layouts/flowlayout/flowlayout.h 0 |
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64 |
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65 We reimplement functions inherited from QLayout. These functions add items to |
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66 the layout and handle their orientation and geometry. |
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67 |
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68 We also declare two private methods, \c doLayout() and \c smartSpacing(). |
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69 \c doLayout() lays out the layout items, while the \c |
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70 smartSpacing() function calculates the spacing between them. |
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71 |
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72 \section1 FlowLayout Class Implementation |
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73 |
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74 We start off by looking at the constructor: |
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75 |
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76 \snippet examples/layouts/flowlayout/flowlayout.cpp 1 |
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77 |
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78 In the constructor we call \c setContentsMargins() to set the left, top, |
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79 right and bottom margin. By default, QLayout uses values provided by |
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80 the current style (see QStyle::PixelMetric). |
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81 |
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82 \snippet examples/layouts/flowlayout/flowlayout.cpp 2 |
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83 |
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84 In this example we reimplement \c addItem(), which is a pure virtual |
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85 function. When using \c addItem() the ownership of the layout items is |
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86 transferred to the layout, and it is therefore the layout's |
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87 responsibility to delete them. |
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88 |
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89 \snippet examples/layouts/flowlayout/flowlayout.cpp 3 |
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90 |
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91 \c addItem() is implemented to add items to the layout. |
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92 |
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93 \snippet examples/layouts/flowlayout/flowlayout.cpp 4 |
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94 |
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95 We implement \c horizontalSpacing() and \c verticalSpacing() to get |
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96 hold of the spacing between the widgets inside the layout. If the value |
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97 is less than or equal to 0, this value will be used. If not, |
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98 \c smartSpacing() will be called to calculate the spacing. |
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99 |
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100 \snippet examples/layouts/flowlayout/flowlayout.cpp 5 |
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101 |
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102 We then implement \c count() to return the number of items in the |
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103 layout. To navigate the list of items we use \c itemAt() and |
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104 takeAt() to remove and return items from the list. If an item is |
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105 removed, the remaining items will be renumbered. All three |
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106 functions are pure virtual functions from QLayout. |
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107 |
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108 \snippet examples/layouts/flowlayout/flowlayout.cpp 6 |
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109 |
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110 \c expandingDirections() returns the \l{Qt::Orientation}s in which the |
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111 layout can make use of more space than its \c sizeHint(). |
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112 |
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113 \snippet examples/layouts/flowlayout/flowlayout.cpp 7 |
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114 |
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115 To adjust to widgets of which height is dependent on width, we implement \c |
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116 heightForWidth(). The function \c hasHeightForWidth() is used to test for this |
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117 dependency, and \c heightForWidth() passes the width on to \c doLayout() which |
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118 in turn uses the width as an argument for the layout rect, i.e., the bounds in |
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119 which the items are laid out. This rect does not include the layout margin(). |
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120 |
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121 \snippet examples/layouts/flowlayout/flowlayout.cpp 8 |
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122 |
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123 \c setGeometry() is normally used to do the actual layout, i.e., calculate |
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124 the geometry of the layout's items. In this example, it calls \c doLayout() |
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125 and passes the layout rect. |
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126 |
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127 \c sizeHint() returns the preferred size of the layout and \c minimumSize() |
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128 returns the minimum size of the layout. |
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129 |
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130 \snippet examples/layouts/flowlayout/flowlayout.cpp 9 |
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131 |
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132 \c doLayout() handles the layout if \c horizontalSpacing() or \c |
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133 verticalSpacing() don't return the default value. It uses |
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134 \c getContentsMargins() to calculate the area available to the |
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135 layout items. |
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136 |
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137 \snippet examples/layouts/flowlayout/flowlayout.cpp 10 |
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138 |
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139 It then sets the proper amount of spacing for each widget in the |
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140 layout, based on the current style. |
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141 |
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142 \snippet examples/layouts/flowlayout/flowlayout.cpp 11 |
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143 |
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144 The position of each item in the layout is then calculated by |
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145 adding the items width and the line height to the initial x and y |
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146 coordinates. This in turn lets us find out whether the next item |
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147 will fit on the current line or if it must be moved down to the next. |
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148 We also find the height of the current line based on the widgets height. |
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149 |
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150 \snippet examples/layouts/flowlayout/flowlayout.cpp 12 |
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151 |
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152 \c smartSpacing() is designed to get the default spacing for either |
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153 the top-level layouts or the sublayouts. The default spacing for |
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154 top-level layouts, when the parent is a QWidget, will be determined |
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155 by querying the style. The default spacing for sublayouts, when |
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156 the parent is a QLayout, will be determined by querying the spacing |
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157 of the parent layout. |
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158 |
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159 */ |