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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). |
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4 ** All rights reserved. |
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7 ** This file is part of the documentation of the Qt Toolkit. |
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16 ** GNU Lesser General Public License Usage |
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36 ** |
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37 ** |
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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 tools/styleplugin |
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44 \title Style Plugin Example |
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45 |
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46 This example shows how to create a plugin that extends Qt with a new |
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47 GUI look and feel. |
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48 |
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49 \image stylepluginexample.png |
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50 |
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51 On some platforms, the native style will prevent the button |
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52 from having a red background. In this case, try to run the example |
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53 in another style (e.g., plastique). |
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54 |
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55 A plugin in Qt is a class stored in a shared library that can be |
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56 loaded by a QPluginLoader at run-time. When you create plugins in |
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57 Qt, they either extend a Qt application or Qt itself. Writing a |
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58 plugin that extends Qt itself is achieved by inheriting one of the |
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59 plugin \l{Plugin Classes}{base classes}, reimplementing functions |
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60 from that class, and adding a macro. In this example we extend Qt |
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61 by adding a new GUI look and feel (i.e., making a new QStyle |
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62 available). A high-level introduction to plugins is given in the |
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63 plugin \l{How to Create Qt Plugins}{overview document}. |
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64 |
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65 Plugins that provide new styles inherit the QStylePlugin base |
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66 class. Style plugins are loaded by Qt and made available through |
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67 QStyleFactory; we will look at this later. We have implemented \c |
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68 SimpleStylePlugin, which provides \c SimpleStyle. The new style |
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69 inherits QWindowsStyle and contributes to widget styling by |
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70 drawing button backgrounds in red - not a major contribution, but |
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71 it still makes a new style. We test the plugin with \c |
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72 StyleWindow, in which we display a QPushButton. |
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73 |
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74 The \c SimpleStyle and \c StyleWindow classes do not contain any |
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75 plugin specific functionality and their implementations are |
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76 trivial; we will therefore leap past them and head on to the \c |
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77 SimpleStylePlugin and the \c main() function. After we have looked |
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78 at that, we examine the plugin's profile. |
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79 |
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80 |
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81 \section1 SimpleStylePlugin Class Definition |
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82 |
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83 \c SimpleStylePlugin inherits QStylePlugin and is the plugin |
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84 class. |
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85 |
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86 \snippet examples/tools/styleplugin/plugin/simplestyleplugin.h 0 |
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87 |
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88 \c keys() returns a list of style names that this plugin can |
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89 create, while \c create() takes such a string and returns the |
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90 QStyle corresponding to the key. Both functions are pure virtual |
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91 functions reimplemented from QStylePlugin. When an application |
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92 requests an instance of the \c SimpleStyle style, which this |
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93 plugin creates, Qt will create it with this plugin. |
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94 |
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95 |
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96 \section1 SimpleStylePlugin Class Implementation |
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97 |
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98 Here is the implementation of \c keys(): |
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99 |
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100 \snippet examples/tools/styleplugin/plugin/simplestyleplugin.cpp 0 |
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101 |
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102 Since this plugin only supports one style, we return a QStringList |
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103 with the class name of that style. |
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104 |
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105 Here is the \c create() function: |
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106 |
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107 \snippet examples/tools/styleplugin/plugin/simplestyleplugin.cpp 1 |
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108 |
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109 Note that the key for style plugins are case insensitive. |
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110 The case sensitivity varies from plugin to plugin, so you need to |
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111 check this when implementing new plugins. |
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112 |
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113 \section1 The \c main() function |
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114 |
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115 \snippet examples/tools/styleplugin/stylewindow/main.cpp 0 |
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116 |
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117 Qt loads the available style plugins when the QApplication object |
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118 is initialized. The QStyleFactory class knows about all styles and |
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119 produces them with \l{QStyleFactory::}{create()} (it is a |
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120 wrapper around all the style plugins). |
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121 |
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122 \section1 The Simple Style Plugin Profile |
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123 |
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124 The \c SimpleStylePlugin lives in its own directory and have |
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125 its own profile: |
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126 |
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127 \snippet examples/tools/styleplugin/plugin/plugin.pro 0 |
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128 |
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129 In the plugin profile we need to set the lib template as we are |
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130 building a shared library instead of an executable. We must also |
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131 set the config to plugin. We set the library to be stored in the |
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132 styles folder under stylewindow because this is a path in which Qt |
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133 will search for style plugins. |
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134 |
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135 \section1 Related articles and examples |
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136 |
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137 In addition to the plugin \l{How to Create Qt Plugins}{overview |
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138 document}, we have other examples and articles that concern |
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139 plugins. |
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140 |
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141 In the \l{Echo Plugin Example}{echo plugin example} we show how to |
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142 implement plugins that extends Qt applications rather than Qt |
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143 itself, which is the case with the style plugin of this example. |
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144 The \l{Plug & Paint Example}{plug & paint} example shows how to |
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145 implement a static plugin as well as being a more involved example |
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146 on plugins that extend applications. |
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147 */ |