The QPluginLoader class loads a plugin at run-time. 更多...
| 頭： | #include <QPluginLoader> |
| 繼承： | QObject |
注意： 此類的所有函數 可重入 .
| QPluginLoader (QObject * parent = 0) | |
| QPluginLoader (const QString & fileName , QObject * parent = 0) | |
| ~QPluginLoader () | |
| QString | errorString () const |
| QString | fileName () const |
| QObject * | instance () |
| bool | isLoaded () const |
| bool | load () |
| QLibrary::LoadHints | loadHints () const |
| void | setFileName (const QString & fileName ) |
| void | setLoadHints (QLibrary::LoadHints loadHints ) |
| bool | unload () |
| QObjectList | staticInstances () |
| void | qRegisterStaticPluginInstanceFunction (QtPluginInstanceFunction function ) |
The QPluginLoader class loads a plugin at run-time.
QPluginLoader provides access to a Qt plugin 。Qt 插件存儲在 DLL 共享庫中並提供這些好處，相比訪問共享庫使用 QLibrary :
An instance of a QPluginLoader object operates on a single shared library file, which we call a plugin. It provides access to the functionality in the plugin in a platform-independent way. To specify which plugin to load, either pass a file name in the constructor or set it with setFileName ().
最重要功能是 load () 用於動態加載插件文件， isLoaded () 用於校驗加載是否成功，及 instance () 用於訪問插件中的根組件。 instance () function implicitly tries to load the plugin if it has not been loaded yet. Multiple instances of QPluginLoader can be used to access the same physical plugin.
Once loaded, plugins remain in memory until all instances of QPluginLoader has been unloaded, or until the application terminates. You can attempt to unload a plugin using unload (), but if other instances of QPluginLoader are using the same library, the call will fail, and unloading will only happen when every instance has called unload (). Right before the unloading happen, the root component will also be deleted.
In order to speed up loading and validation of plugins, some of the information that is collected during loading is cached in persistent memory (through QSettings ). For instance, the result of a load operation (e.g. succeeded or failed) is stored in the cache, so that subsequent load operations don't try to load an invalid plugin. However, if the "last modified" timestamp of a plugin has changed, the plugin's cache entry is invalidated and the plugin is reloaded regardless of the values in the cache entry. The cache entry is then updated with the new result of the load operation.
This also means that the timestamp must be updated each time the plugin or any dependent resources (such as a shared library) is updated, since the dependent resources might influence the result of loading a plugin.
見 如何創建 Qt 插件 for more information about how to make your application extensible through plugins.
注意， QPluginLoader cannot be used if your application is statically linked against Qt. In this case, you will also have to link to plugins statically. You can use QLibrary if you need to load dynamic libraries in a statically linked application.
注意： In Symbian the plugin stub files must be used whenever a path to plugin is needed. For the purposes of loading plugins, the stubs can be considered to have the same name as the actual plugin binary. In practice they have ".qtplugin" extension instead of ".dll", but this difference is handled transparently by QPluginLoader and QLibrary to avoid need for Symbian specific plugin handling in most Qt applications. Plugin stubs are needed because Symbian Platform Security denies all access to the directory where the actual plugin binaries are located.
This property holds the file name of the plugin.
要可加載，文件後綴必須是與平颱一緻的有效可加載庫後綴，如
.so
on Unix,
.dylib
on Mac OS X, and
.dll
在 Windows。可以驗證後綴采用
QLibrary::isLibrary
().
If the file name does not exist, it will not be set. This property will then contain an empty string.
默認情況下，此特性包含空字符串。
Note: In Symbian the fileName must point to plugin stub file.
訪問函數：
| QString | fileName () const |
| void | setFileName (const QString & fileName ) |
另請參閱 load ().
This property holds give the load() function some hints on how it should behave.
You can give hints on how the symbols in the plugin are resolved. By default, none of the hints are set.
See the documentation of QLibrary::loadHints for a complete description of how this property works.
該特性在 Qt 4.4 引入。
訪問函數：
| QLibrary::LoadHints | loadHints () const |
| void | setLoadHints (QLibrary::LoadHints loadHints ) |
另請參閱 QLibrary::loadHints .
構造插件加載器采用給定 parent .
構造插件加載器采用給定 parent 將加載指定插件通過 fileName .
要可加載，文件後綴必須是與平颱一緻的有效可加載庫後綴，如
.so
在 Unix，
.dylib
on Mac OS X, and
.dll
在 Windows。可以驗證後綴采用
QLibrary::isLibrary
().
Note: In Symbian the fileName must point to plugin stub file.
另請參閱 setFileName ().
銷毀 QPluginLoader 對象。
除非 unload () was called explicitly, the plugin stays in memory until the application terminates.
Returns a text string with the description of the last error that occurred.
該函數在 Qt 4.2 引入。
Returns the root component object of the plugin. The plugin is loaded if necessary. The function returns 0 if the plugin could not be loaded or if the root component object could not be instantiated.
若根組件對象被銷毀，調用此函創建新實例。
不會刪除由此函數返迴的根組件當 QPluginLoader 被銷毀時。若想要確保刪除根組件，應該調用 unload () 隻要不再需要訪問核心組件。當庫被最終卸載時，將自動刪除根組件。
組件對象是 QObject 。使用 qobject_cast () 訪問感興趣接口。
另請參閱 load ().
Returns true if the plugin is loaded; otherwise returns false.
另請參閱 load ().
Loads the plugin and returns true if the plugin was loaded successfully; otherwise returns false. Since instance () always calls this function before resolving any symbols it is not necessary to call it explicitly. In some situations you might want the plugin loaded in advance, in which case you would use this function.
另請參閱 unload ().
[static]
QObjectList
QPluginLoader::
staticInstances
()
Returns a list of static plugin instances (root components) held by the plugin loader.
Unloads the plugin and returns true if the plugin could be unloaded; otherwise returns false.
This happens automatically on application termination, so you shouldn't normally need to call this function.
If other instances of QPluginLoader are using the same plugin, the call will fail, and unloading will only happen when every instance has called unload().
Don't try to delete the root component. Instead rely on that unload() will automatically delete it when needed.
注冊給定 function with the plugin loader.
該函數在 Qt 4.4 引入。