CopperSpice API  1.7.2
QPluginLoader Class Reference

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

Inheritance diagram for QPluginLoader:
QObject

Public Methods

 QPluginLoader (const QString &fileName, QObject *parent=nullptr)
 
 QPluginLoader (QObject *parent=nullptr)
 
 ~QPluginLoader ()
 
QString errorString () const
 
QString fileName () const
 
QObjectinstance ()
 
bool isLoaded () const
 
bool load ()
 
QLibrary::LoadHints loadHints () const
 
void setFileName (const QString &fileName)
 
void setLoadHints (QLibrary::LoadHints loadHints)
 
bool unload ()
 
- Public Methods inherited from QObject
 QObject (QObject *parent=nullptr)
 
 ~QObject ()
 
bool blockSignals (bool block)
 
const QList< QObject * > & children () const
 
bool connect (const QObject *sender, const QString &signalMethod, const QString &location, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
 
bool connect (const QObject *sender, const QString &signalMethod, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
 
bool disconnect (const QObject *receiver, const QString &slotMethod=QString ()) const
 
bool disconnect (const QString &signalMethod, const QString &location, const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const
 
bool disconnect (const QString &signalMethod=QString (), const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const
 
void dumpObjectInfo ()
 
void dumpObjectTree ()
 
QList< QStringdynamicPropertyNames () const
 
virtual bool event (QEvent *event)
 
virtual bool eventFilter (QObject *watched, QEvent *event)
 
template<typename T >
findChild (const QString &childName=QString ()) const
 
template<class T >
QList< T > findChildren (const QRegularExpression &regExp, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
 
template<class T >
QList< T > findChildren (const QString &objName=QString (), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
 
bool inherits (const QString &className) const
 
void installEventFilter (QObject *filterObj)
 
bool isWidgetType () const
 
bool isWindowType () const
 
void killTimer (int id)
 
const QMetaObjectmetaObject () const
 
void moveToThread (QThread *targetThread)
 
QString objectName () const
 
QObject * parent () const
 
template<class T = QVariant>
property (const QString &name) const
 
void removeEventFilter (QObject *obj)
 
void setObjectName (const QString &name)
 
void setParent (QObject *parent)
 
bool setProperty (const QString &name, const QVariant &value)
 
bool signalsBlocked () const
 
int startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)
 
QThreadthread () const
 

Static Public Methods

static QObjectList staticInstances ()
 
static QVector< QMetaObject * > staticPlugins ()
 
- Static Public Methods inherited from QObject
static bool connect (const QObject *sender, const QMetaMethod &signalMethod, const QObject *receiver, const QMetaMethod &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
 
static bool connect (const QObject *sender, const QString &signalMethod, const QObject *receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection, const QString &location=QString ())
 
static bool connect (const QObject *sender, const QString &signalMethod, const QString &location, const QObject *receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
 
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool connect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, SlotReturn (SlotClass::*slotMethod)(SlotArgs...), Qt::ConnectionType type=Qt::AutoConnection)
 
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool connect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, T slotLambda, Qt::ConnectionType type=Qt::AutoConnection)
 
static bool disconnect (const QObject *sender, const QMetaMethod &signalMethod, const QObject *receiver, const QMetaMethod &slotMethod)
 
static bool disconnect (const QObject *sender, const QString &signalMethod, const QObject *receiver, const QString &slotMethod)
 
static bool disconnect (const QObject *sender, const QString &signalMethod, const QString &location, const QObject *receiver, const QString &slotMethod)
 
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool disconnect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, SlotReturn (SlotClass::*slotMethod)(SlotArgs...))
 
template<class Sender , class SignalClass , class... SignalArgs, class Receiver >
static bool disconnect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, std::nullptr_t slotMethod=nullptr)
 
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool disconnect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, T slotMethod)
 
static QMetaObjectstaticMetaObject ()
 
static QString tr (const char *text, const char *comment=nullptr, std::optional< int > numArg=std::optional< int >())
 

Properties

 fileName
 
 loadHints
 
- Properties inherited from QObject
 objectName
 

Additional Inherited Members

- Public Signals inherited from QObject
void destroyed (QObject *obj=nullptr)
 
void objectNameChanged (const QString &objectName)
 
- Public Slots inherited from QObject
void deleteLater ()
 
- Protected Methods inherited from QObject
virtual void childEvent (QChildEvent *event)
 
virtual void connectNotify (const QMetaMethod &signalMethod) const
 
virtual void customEvent (QEvent *event)
 
virtual void disconnectNotify (const QMetaMethod &signalMethod) const
 
bool isSignalConnected (const QMetaMethod &signalMethod) const
 
int receivers (const QString &signal) const
 
QObject * sender () const
 
int senderSignalIndex () const
 
virtual void timerEvent (QTimerEvent *event)
 

Detailed Description

The QPluginLoader class loads a plugin at run-time. A plugin is stored in a shared library (usually a .DLL or .SO file) and offers several benefits over shared libraries accessed using QLibrary.

  • QPluginLoader verify that a plugin is linked with the same version of CopperSpice as the user application
  • QPluginLoader provides direct access to an object exported by the plugin

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().

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 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 do not 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.

The QPluginLoader can not be used if your application is statically linked with CopperSpice. 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.

Refer to Creating Plugins for more information about extending your application through plugins.

See also
QLibrary

Constructor & Destructor Documentation

QPluginLoader::QPluginLoader ( QObject parent = nullptr)
explicit

Constructs a plugin loader with the given parent.

QPluginLoader::QPluginLoader ( const QString fileName,
QObject parent = nullptr 
)
explicit

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(), unload()

Method Documentation

QString QPluginLoader::errorString ( ) const

Returns a text string with the description of the last error that occurred.

QString QPluginLoader::fileName ( ) const

Returns the value of the property fileName.

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 root component, returned by this function, is not deleted when the QPluginLoader is destroyed. If you want to ensure that the root component is deleted, you should call unload() as soon you do not need to access the core component anymore. When the library is finally unloaded, the root component will automatically be deleted.

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.

See also
unload()
QLibrary::LoadHints QPluginLoader::loadHints ( ) const

Returns the value of the property loadHints.

void QPluginLoader::setFileName ( const QString fileName)

Sets the value of the property fileName to fileName.

void QPluginLoader::setLoadHints ( QLibrary::LoadHints  loadHints)

Sets the value of the property loadHints to hints.

QObjectList QPluginLoader::staticInstances ( )
static

Returns a list of static plugin instances (root components) held by the plugin loader.

QVector< QMetaObject * > QPluginLoader::staticPlugins ( )
static

Returns a list of QStaticPlugins held by the plugin loader. The function is similar to staticInstances() with the addition that a QStaticPlugin also contains meta data information.

See also
staticInstances()
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 should not 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().

Do not try to delete the root component. Instead rely on that unload() will automatically delete it when needed.

See also
instance(), load()

Property Documentation

QPluginLoader::fileName

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().

If the file name does not exist there this property will then contain an empty string. By default, this property contains an empty string.

See also
load()
PropertiesClass Methods
read fileName
write setFileName
QPluginLoader::loadHints

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. Refer to the documentation for QLibrary::loadHints for a complete description of how this property works.

See also
QLibrary::loadHints
PropertiesClass Methods
read loadHints
write setLoadHints