Home · All Classes · Main Classes · Annotated · Grouped Classes · Functions

QPluginLoader Class Reference

The QPluginLoader class loads a plugin at run-time. More...

#include <QPluginLoader>

Part of the QtCore module.

Inherits QObject.

Note: All the functions in this class are reentrant.

Properties

Public Functions

Static Public Members

Macros

Additional Inherited Members


Detailed Description

The QPluginLoader class loads a plugin at run-time.

QPlugingLoader provides a means for accessing a Qt plugin. Qt plugins are stored in a shared library (a "DLL") and follow offer a few benefits over plain shared libraries accessed using 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, you can either pass a file name in the constructor or set it with setFileName().

The most important functions are load() to dynamically load the plugin file, isLoaded() to check whether loading was successful, and instance() to access the root component in the plugin. The 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 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().

See How to Create Qt Plugins for more information about how to make your application extensible through plugins.

See also QLibrary.


Property Documentation

fileName : QString

This property holds the file name of the plugin.

To be loadable, the file's suffix must be a valid suffix for a loadable library in accordance with the platform, e.g. .so on Unix, - .dylib on Mac OS X, and .dll on Windows. The suffix can be verified with QLibrary::isLibrary().

Access functions:

See also load().


Member Function Documentation

QPluginLoader::QPluginLoader ( QObject * parent = 0 )

Constructs a plugin loader with the given parent.

QPluginLoader::QPluginLoader ( const QString & fileName, QObject * parent = 0 )

Constructs a plugin loader with the given parent that will load the plugin specified by fileName.

To be loadable, the file's suffix must be a valid suffix for a loadable library in accordance with the platform, e.g. .so on Unix, - .dylib on Mac OS X, and .dll on Windows. The suffix can be verified with QLibrary::isLibrary().

See also setFileName().

QPluginLoader::~QPluginLoader ()

Destroys the QPluginLoader object.

Unless unload() was called explicitly, the plugin stays in memory until the application terminates.

See also isLoaded() and unload().

QObject * QPluginLoader::instance ()

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.

If the root component object was destroyed, calling this function creates a new instance.

The instance is not deleted when the QPluginLoader is destroyed.

The component object is a QObject. Use qobject_cast() to access interfaces you are interested in.

See also load().

bool QPluginLoader::isLoaded () const

Returns true if the plugin is loaded; otherwise returns false.

See also load().

bool QPluginLoader::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.

On Darwin and Mac OS X this function uses code from dlcompat, part of the OpenDarwin project.

    Copyright (c) 2002 Jorge Acereda and Peter O'Gorman.

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
    LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

See also unload().

QObjectList QPluginLoader::staticInstances ()   [static]

bool QPluginLoader::unload ()

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().

See also instance() and load().


Macro Documentation

Q_DECLARE_INTERFACE ( ClassName, Identifier )

This macro associates the given Identifier (a string literal) to the interface class called ClassName.

Example:

    Q_DECLARE_INTERFACE(BrushInterface,
                        "com.trolltech.PlugAndPaint.BrushInterface/1.0")

This macro is normally used right after the class definition for ClassName, in a header file. See the Plug & Paint example for details.

See also Q_INTERFACE(), Q_EXPORT_PLUGIN(), and How to Create Qt Plugins.

Q_EXPORT_PLUGIN ( ClassName )

This macro exports the plugin class ClassName. There should be exactly one occurrence of this macro in a Qt plugin's source code (in an implementation file).

Example:

    Q_EXPORT_PLUGIN(ExtraFiltersPlugin)

See the Plug & Paint example for details.

See also Q_DECLARE_INTERFACE() and How to Create Qt Plugins.


Copyright © 2005 Trolltech Trademarks
Qt 4.0.0-rc1