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

#include <qimageiohandler.h>

Inheritance diagram for QImageIOPlugin:

Collaboration diagram for QImageIOPlugin:

Public Types
enum	Capability { CanRead = 0x1 , CanWrite = 0x2 , CanReadIncremental = 0x4 }

Public Member Functions
	QImageIOPlugin (QObject *parent=nullptr)

	~QImageIOPlugin ()

virtual Capabilities	capabilities (QIODevice *device, const QByteArray &format) const =0

virtual QImageIOHandler *	create (QIODevice *device, const QByteArray &format=QByteArray()) const =0

Public Member Functions inherited from QObject
Q_INVOKABLE	QObject (QObject *parent=nullptr)

virtual	~QObject ()

virtual bool	event (QEvent *event)

virtual bool	eventFilter (QObject watched, QEvent event)

QString	objectName () const

void	setObjectName (const QString &name)

QBindable< QString >	bindableObjectName ()

bool	isWidgetType () const

bool	isWindowType () const

bool	signalsBlocked () const noexcept

bool	blockSignals (bool b) noexcept

QThread *	thread () const

void	moveToThread (QThread *thread)

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)

void	killTimer (int id)

template<typename T >
T	findChild (const QString &aName=QString(), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<typename T >
QList< T >	findChildren (const QString &aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<typename T >
QList< T >	findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

const QObjectList &	children () const

void	setParent (QObject *parent)

void	installEventFilter (QObject *filterObj)

void	removeEventFilter (QObject *obj)

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

void	dumpObjectInfo () const

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

QVariant	property (const char *name) const

QList< QByteArray >	dynamicPropertyNames () const

QBindingStorage *	bindingStorage ()

const QBindingStorage *	bindingStorage () const

QObject *	parent () const

bool	inherits (const char *classname) const

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

Signals inherited from QObject
void	destroyed (QObject *=nullptr)

void	objectNameChanged (const QString &objectName, QPrivateSignal)

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)

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::FunctionPointer< Func2 >::Object receiver, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

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

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

template<typename Func1 , typename Func2 >
static std::enable_if< QtPrivate::FunctionPointer< Func2 >::ArgumentCount==-1 &&!std::is_convertible_v< Func2, const char * >, QMetaObject::Connection >::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 slot)

template<typename Func1 , typename Func2 >
static std::enable_if< QtPrivate::FunctionPointer< Func2 >::ArgumentCount==-1 &&!std::is_convertible_v< Func2, const char * >, QMetaObject::Connection >::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject context, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

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

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

static bool	disconnect (const QMetaObject::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

int	senderSignalIndex () const

int	receivers (const char *signal) const

bool	isSignalConnected (const QMetaMethod &signal) const

virtual void	timerEvent (QTimerEvent *event)

virtual void	childEvent (QChildEvent *event)

virtual void	customEvent (QEvent *event)

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 More...

Related Functions inherited from QObject
template< class T > T	qobject_cast (const QObject *object)

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

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

	QObjectList

Detailed Description

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

\inmodule QtGui

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 137 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 144 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 606 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 617 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 QJpegPlugin, QICOPlugin, and QGifPlugin.

Here is the caller graph for this function:

◆ create()

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