Contents

• Public Types
• Public Functions
• Reimplemented Public Functions
• Detailed Description

Detailed Description

TheQImageIOPlugin class defines an interface for writing an image format plugin.

QImageIOPlugin is a factory for creatingQImageIOHandler objects, which are used internally byQImageReader andQImageWriter 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 functionscapabilities(),create(), andkeys(), and exporting the class with theQ_EXPORT_PLUGIN2() macro. SeeHow to Create Qt Plugins for details.

An image format plugin can support three capabilities: reading (CanRead), writing (CanWrite) andincremental reading (CanReadIncremental). Reimplementcapabilities() in you subclass to expose the capabilities of your image format.

create() should create an instance of yourQImageIOHandler subclass, with the provided device and format properly set, and return this handler. You must also reimplementkeys() so that Qt knows which image formats your plugin supports.

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 ofcapabilities(). If several plugins support the same capability, Qt will select one arbitrarily.

Member Type Documentation

enum QImageIOPlugin::Capability
flags QImageIOPlugin::Capabilities

This enum describes the capabilities of aQImageIOPlugin.

The Capabilities type is a typedef forQFlags<Capability>. It stores an OR combination of Capability values.

Member Function Documentation

QImageIOPlugin::QImageIOPlugin(QObject * parent = 0)

Constructs an image plugin with the givenparent. This is invoked automatically by theQ_EXPORT_PLUGIN2() macro.

[virtual]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.

[pure virtual]Capabilities QImageIOPlugin::capabilities(QIODevice * device, constQByteArray & format) const

Returns the capabilities on the plugin, based on the data indevice and the formatformat. For example, if theQImageIOHandler supports the BMP format, and the data in the device starts with the characters "BM", this function should returnCanRead. Ifformat is "bmp" and the handler supports both reading and writing, this function should returnCanRead |CanWrite.

[pure virtual]QImageIOHandler * QImageIOPlugin::create(QIODevice * device, constQByteArray & format = QByteArray()) const

Creates and returns aQImageIOHandler subclass, withdevice andformat set. Theformat must come from the list returned bykeys(). Format names are case sensitive.

See alsokeys().

[pure virtual]QStringList QImageIOPlugin::keys() const

Returns the list of image keys this plugin supports.

These keys are usually the names of the image formats that are implemented in the plugin (e.g., "jpg" or "gif").

See alsocapabilities().