\inmodule QtGui More...

#include <qimageiohandler.h>

Inheritance diagram for QImageIOPlugin:

Collaboration diagram for QImageIOPlugin:

Public Types
enum	Capability { CanRead = 0x1 , CanWrite = 0x2 , CanReadIncremental = 0x4 }
	This enum describes the capabilities of a QImageIOPlugin. More...

Public Member Functions
	QImageIOPlugin (QObject *parent=nullptr)
	Constructs an image plugin with the given parent.

	~QImageIOPlugin ()
	Destroys the picture format plugin.

virtual Capabilities	capabilities (QIODevice *device, const QByteArray &format) const =0
	Returns the capabilities of the plugin, based on the data in device and the format format.

virtual QImageIOHandler *	create (QIODevice *device, const QByteArray &format=QByteArray()) const =0
	Creates and returns a QImageIOHandler subclass, with device and format set.

Public Member Functions inherited from QObject
Q_INVOKABLE	QObject (QObject *parent=nullptr)
	Constructs an object with parent object parent.

virtual	~QObject ()
	Destroys the object, deleting all its child objects.

virtual bool	event (QEvent *event)
	This virtual function receives events to an object and should return true if the event e was recognized and processed.

virtual bool	eventFilter (QObject watched, QEvent event)
	Filters events if this object has been installed as an event filter for the watched object.

QString	objectName () const

Q_WEAK_OVERLOAD void	setObjectName (const QString &name)
	Sets the object's name to name.

void	setObjectName (QAnyStringView name)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

QBindable< QString >	bindableObjectName ()

bool	isWidgetType () const
	Returns `true` if the object is a widget; otherwise returns `false`.

bool	isWindowType () const
	Returns `true` if the object is a window; otherwise returns `false`.

bool	isQuickItemType () const
	Returns `true` if the object is a QQuickItem; otherwise returns `false`.

bool	signalsBlocked () const noexcept
	Returns `true` if signals are blocked; otherwise returns `false`.

bool	blockSignals (bool b) noexcept
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it).

QThread *	thread () const
	Returns the thread in which the object lives.

void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children.

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)
	This is an overloaded function that will start a timer of type timerType and a timeout of interval milliseconds.

int	startTimer (std::chrono::milliseconds time, Qt::TimerType timerType=Qt::CoarseTimer)

void	killTimer (int id)
	Kills the timer with timer identifier, id.

template<typename T >
T	findChild (const QString &aName=QString(), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns the child of this object that can be cast into type T and that is called name, or \nullptr if there is no such object.

template<typename T >
QList< T >	findChildren (const QString &aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects.

template<typename T >
QList< T >	findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

const QObjectList &	children () const
	Returns a list of child objects.

void	setParent (QObject *parent)
	Makes the object a child of parent.

void	installEventFilter (QObject *filterObj)
	Installs an event filter filterObj on this object.

void	removeEventFilter (QObject *obj)
	Removes an event filter object obj from this object.

QMetaObject::Connection	connect (const QObject sender, const char signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const

bool	disconnect (const char signal=nullptr, const QObject receiver=nullptr, const char *member=nullptr) const

bool	disconnect (const QObject receiver, const char member=nullptr) const

void	dumpObjectTree () const
	Dumps a tree of children to the debug output.

void	dumpObjectInfo () const
	Dumps information about signal connections, etc.

bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value.

bool	setProperty (const char *name, QVariant &&value)

QVariant	property (const char *name) const
	Returns the value of the object's name property.

QList< QByteArray >	dynamicPropertyNames () const

QBindingStorage *	bindingStorage ()

const QBindingStorage *	bindingStorage () const

QObject *	parent () const
	Returns a pointer to the parent object.

bool	inherits (const char *classname) const
	Returns `true` if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns `false`.

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	\threadsafe

Signals inherited from QObject
void	destroyed (QObject *=nullptr)
	This signal is emitted immediately before the object obj is destroyed, after any instances of QPointer have been notified, and cannot be blocked.

void	objectNameChanged (const QString &objectName, QPrivateSignal)
	This signal is emitted after the object's name has been changed.

Static Public Member Functions inherited from QObject
static QMetaObject::Connection	connect (const QObject sender, const char signal, const QObject receiver, const char member, Qt::ConnectionType=Qt::AutoConnection)
	\threadsafe

static QMetaObject::Connection	connect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::ContextTypeForFunctor< Func2 >::ContextType context, Func2 &&slot, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 &&slot)

static bool	disconnect (const QObject sender, const char signal, const QObject receiver, const char member)
	\threadsafe

static bool	disconnect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &member)

static bool	disconnect (const QMetaObject::Connection &)
	Disconnect a connection.

template<typename Func1 , typename Func2 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object receiver, Func2 slot)

template<typename Func1 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject receiver, void **zero)

Protected Member Functions inherited from QObject
QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns \nullptr.

int	senderSignalIndex () const

int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal.

bool	isSignalConnected (const QMetaMethod &signal) const

virtual void	timerEvent (QTimerEvent *event)
	This event handler can be reimplemented in a subclass to receive timer events for the object.

virtual void	childEvent (QChildEvent *event)
	This event handler can be reimplemented in a subclass to receive child events.

virtual void	customEvent (QEvent *event)
	This event handler can be reimplemented in a subclass to receive custom events.

virtual void	connectNotify (const QMetaMethod &signal)

virtual void	disconnectNotify (const QMetaMethod &signal)

	QObject (QObjectPrivate &dd, QObject *parent=nullptr)

Protected Attributes inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Properties inherited from QObject
QString	objectName
	the name of this object

Related Symbols inherited from QObject
template< class T > T	qobject_cast (const QObject *object)
	Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns \nullptr.

template< typename T > T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

template< typename T > QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

	QObjectList
	\macro Q_CLASSINFO(Name, Value)

Detailed Description

\inmodule QtGui

The QImageIOPlugin class defines an interface for writing an image format plugin. \reentrant

QImageIOPlugin is a factory for creating QImageIOHandler objects, which are used internally by QImageReader and QImageWriter to add support for different image formats to Qt.

Writing an image I/O plugin is achieved by subclassing this base class, reimplementing the pure virtual functions capabilities() and create(), and exporting the class with the Q_PLUGIN_METADATA() macro. See \l{How to Create Qt Plugins} for details.

An image format plugin can support three capabilities: reading (\l CanRead), writing (\l CanWrite) and incremental reading (\l CanReadIncremental). Reimplement capabilities() in your subclass to expose the capabilities of your image format.

create() should create an instance of your QImageIOHandler subclass, with the provided device and format properly set, and return this handler.

The json metadata file for the plugin needs to contain information about the image formats the plugins supports, together with the corresponding MIME types (one for each format). For a jpeg plugin, this could, for example, look as follows:

{
  "Keys": [ "jpg", "jpeg" ],
  "MimeTypes": [ "image/jpeg", "image/jpeg" ]
}

Different plugins can support different capabilities. For example, you may have one plugin that supports reading the GIF format, and another that supports writing. Qt will select the correct plugin for the job, depending on the return value of capabilities(). If several plugins support the same capability, Qt will select one arbitrarily.

See also: QImageIOHandler, {How to Create Qt Plugins}

Definition at line 101 of file qimageiohandler.h.

Member Enumeration Documentation

◆ Capability

enum QImageIOPlugin::Capability

This enum describes the capabilities of a QImageIOPlugin.

\value CanRead The plugin can read images. \value CanWrite The plugin can write images. \value CanReadIncremental The plugin can read images incrementally.

Enumerator
CanRead
CanWrite
CanReadIncremental

Definition at line 108 of file qimageiohandler.h.

Constructor & Destructor Documentation

◆ QImageIOPlugin()

QImageIOPlugin::QImageIOPlugin ( QObject * parent = nullptr )

explicit

Constructs an image plugin with the given parent.

This is invoked automatically by the moc generated code that exports the plugin.

Definition at line 565 of file qimageiohandler.cpp.

◆ ~QImageIOPlugin()

QImageIOPlugin::~QImageIOPlugin ( )

Destroys the picture format plugin.

You never have to call this explicitly. Qt destroys a plugin automatically when it is no longer used.

Definition at line 576 of file qimageiohandler.cpp.

Member Function Documentation

◆ capabilities()

QImageIOPlugin::capabilities	(	QIODevice *	device,
		const QByteArray &	format
	)		const

pure virtual

Returns the capabilities of the plugin, based on the data in device and the format format.

If device is 0, it should simply report whether the format can be read or written. Otherwise, it should attempt to determine whether the given format (or any format supported by the plugin if format is empty) can be read from or written to device. It should do this without changing the state of device (typically by using QIODevice::peek()).

For example, if the QImageIOPlugin supports the BMP format, format is either empty or "bmp", and the data in the device starts with the characters "BM", this function should return \l CanRead. If format is "bmp", device is 0 and the handler supports both reading and writing, this function should return \l CanRead | \l CanWrite.

Format names are always given in lower case.

Implemented in QGifPlugin, QICOPlugin, QJpegPlugin, QDDSPlugin, QICNSPlugin, QJp2Plugin, QMacHeifPlugin, QMacJp2Plugin, QMngPlugin, QTgaPlugin, QTiffPlugin, QWbmpPlugin, QWebpPlugin, QSvgPlugin, and QPdfPlugin.

Referenced by QImageReaderWriterHelpers::appendImagePluginMimeTypes(), createReadHandlerHelper(), and createWriteHandlerHelper().

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◆ create()

QImageIOHandler * QImageIOPlugin::create	(	QIODevice *	device,
		const QByteArray &	format = `QByteArray()`
	)		const

pure virtual

Creates and returns a QImageIOHandler subclass, with device and format set.

The format must come from the values listed in the "Keys" entry in the plugin metadata, or be empty. If it is empty, the data in device must have been recognized by the capabilities() method (with a likewise empty format).