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</style></head><body><table border="0" cellpadding="0" cellspacing="0" width="100%"><tr /><td align="left" valign="top" width="32"><img align="left" border="0" height="32" src="images/rb-logo.png" width="32" /></td><td width="1">  </td><td class="postheader" valign="center"><a href="../pyqt4ref.html"><font color="#004faf">Home</font></a> · <a href="classes.html"><font color="#004faf">All Classes</font></a> · <a href="modules.html"><font color="#004faf">Modules</font></a></td></table><h1 align="center">QDeclarativeImageProvider Class Reference<br /><sup><sup>[<a href="qtdeclarative.html">QtDeclarative</a> module]</sup></sup></h1><p>The QDeclarativeImageProvider class provides an interface for
supporting pixmaps and threaded image requests in QML. <a href="#details">More...</a></p>
<h3>Types</h3><ul><li><div class="fn" />enum <b><a href="qdeclarativeimageprovider.html#ImageType-enum">ImageType</a></b> { Image, Pixmap }</li></ul><h3>Methods</h3><ul><li><div class="fn" /><b><a href="qdeclarativeimageprovider.html#QDeclarativeImageProvider">__init__</a></b> (<i>self</i>, ImageType <i>type</i>)</li><li><div class="fn" /><b><a href="qdeclarativeimageprovider.html#QDeclarativeImageProvider-2">__init__</a></b> (<i>self</i>, QDeclarativeImageProvider)</li><li><div class="fn" />ImageType <b><a href="qdeclarativeimageprovider.html#imageType">imageType</a></b> (<i>self</i>)</li><li><div class="fn" />QImage <b><a href="qdeclarativeimageprovider.html#requestImage">requestImage</a></b> (<i>self</i>, QString <i>id</i>, QSize <i>size</i>, QSize <i>requestedSize</i>)</li><li><div class="fn" />QPixmap <b><a href="qdeclarativeimageprovider.html#requestPixmap">requestPixmap</a></b> (<i>self</i>, QString <i>id</i>, QSize <i>size</i>, QSize <i>requestedSize</i>)</li></ul><a name="details" /><hr /><h2>Detailed Description</h2><p>The QDeclarativeImageProvider class provides an interface for
supporting pixmaps and threaded image requests in QML.</p>
<p>QDeclarativeImageProvider is used to provide advanced image
loading features in QML applications. It allows images in QML to
be:</p>
<ul>
<li>Loaded using QPixmaps rather than actual image files</li>
<li>Loaded asynchronously in a separate thread, if <a href="qdeclarativeimageprovider.html#imageType">imageType</a>() is
<a href="qdeclarativeimageprovider.html#ImageType-enum">ImageType.Image</a></li>
</ul>
<p>To specify that an image should be loaded by an image provider,
use the <b>"image:"</b> scheme for the URL source of the image,
followed by the identifiers of the image provider and the requested
image. For example:</p>
<pre class="highlightedCode brush: cpp">
Image { source: "image://myimageprovider/image.png" }
</pre>
<p>This specifies that the image should be loaded by the image
provider named "myimageprovider", and the image to be loaded is
named "image.png". The QML engine invokes the appropriate image
provider according to the providers that have been registered
through <a href="qdeclarativeengine.html#addImageProvider">QDeclarativeEngine.addImageProvider</a>().</p>
<a id="an-example" name="an-example" />
<h3>An example</h3>
<p>Here are two images. Their <tt>source</tt> values indicate they
should be loaded by an image provider named "colors", and the
images to be loaded are "yellow" and "red", respectively:</p>
<pre class="highlightedCode brush: cpp">
Column {
Image { source: "image://colors/yellow" }
Image { source: "image://colors/red" }
}
</pre>
<p>When these images are loaded by QML, it looks for a matching
image provider and calls its <a href="qdeclarativeimageprovider.html#requestImage">requestImage</a>() or
<a href="qdeclarativeimageprovider.html#requestPixmap">requestPixmap</a>()
method (depending on its <a href="qdeclarativeimageprovider.html#imageType">imageType</a>()) to load
the image. The method is called with the <tt>id</tt> parameter set
to "yellow" for the first image, and "red" for the second.</p>
<p>Here is an image provider implementation that can load the
images requested by the above QML. This implementation dynamically
generates <a href="qpixmap.html">QPixmap</a> images that are filled
with the requested color:</p>
<pre class="highlightedCode brush: cpp">
class ColorImageProvider : public QDeclarativeImageProvider
{
public:
ColorImageProvider()
: QDeclarativeImageProvider(QDeclarativeImageProvider.Pixmap)
{
}
QPixmap requestPixmap(const QString &id, QSize *size, const QSize &requestedSize)
{
int width = 100;
int height = 50;
if (size)
*size = QSize(width, height);
QPixmap pixmap(requestedSize.width() > 0 ? requestedSize.width() : width,
requestedSize.height() > 0 ? requestedSize.height() : height);
pixmap.fill(QColor(id).rgba());
return pixmap;
}
};
</pre>
<p>To make this provider accessible to QML, it is registered with
the QML engine with a "colors" identifier:</p>
<pre class="highlightedCode brush: cpp">
int main(int argc, char *argv[])
{
...
QDeclarativeEngine engine;
engine->addImageProvider(QLatin1String("colors"), new ColorPixmapProvider);
...
}
</pre>
<p>Now the images can be successfully loaded in QML:</p>
<p class="centerAlign"><img src="images/imageprovider.png" /></p>
<p>A complete example is available in Qt's <a href="declarative-cppextensions-imageprovider.html">examples/declarative/cppextensions/imageprovider</a>
directory. Note the example registers the provider via a <a href="qdeclarativeextensionplugin.html">plugin</a> instead of
registering it in the application <tt>main()</tt> function as shown
above.</p>
<a id="asynchronous-image-loading" name="asynchronous-image-loading" />
<h3>Asynchronous image loading</h3>
<p>Image providers that support <a href="qimage.html">QImage</a>
loading automatically include support for asychronous loading of
images. To enable asynchronous loading for an <a href="qdeclarativeimageprovider.html#ImageType-enum">Image</a> source,
set <a href="qml-image.html#asynchronous-prop">Image.asynchronous</a> to
<tt>true</tt>. When this is enabled, the image request to the
provider is run in a low priority thread, allowing image loading to
be executed in the background, and reducing the performance impact
on the user interface.</p>
<p>Asynchronous loading is not supported for image providers that
provide <a href="qpixmap.html">QPixmap</a> rather than <a href="qimage.html">QImage</a> values, as pixmaps can only be created in
the main thread. In this case, if <a href="qml-image.html#asynchronous-prop">asynchronous</a> is set to
<tt>true</tt>, the value is ignored and the image is loaded
synchronously.</p>
<hr /><h2>Type Documentation</h2><h3 class="fn"><a name="ImageType-enum" />QDeclarativeImageProvider.ImageType</h3><p>Defines the type of image supported by this image provider.</p>
<table class="valuelist">
<tr class="odd">
<td />
</tr>
<tr>
<th class="tblConst">Constant</th>
<th class="tblval">Value</th>
<th class="tbldscr">Description</th>
</tr>
<tr>
<td class="topAlign"><tt>QDeclarativeImageProvider.Image</tt></td>
<td class=" topAlign"><tt>0</tt></td>
<td class="topAlign">The Image Provider provides <a href="qimage.html">QImage</a> images. The <a href="qdeclarativeimageprovider.html#requestImage">requestImage</a>()
method will be called for all image requests.</td>
</tr>
<tr>
<td class="topAlign">
<tt>QDeclarativeImageProvider.Pixmap</tt></td>
<td class=" topAlign"><tt>1</tt></td>
<td class="topAlign">The Image Provider provides <a href="qpixmap.html">QPixmap</a> images. The <a href="qdeclarativeimageprovider.html#requestPixmap">requestPixmap</a>()
method will be called for all image requests.</td>
</tr>
</table>
<hr /><h2>Method Documentation</h2><h3 class="fn"><a name="QDeclarativeImageProvider" />QDeclarativeImageProvider.__init__ (<i>self</i>, <a href="qdeclarativeimageprovider.html#ImageType-enum">ImageType</a> <i>type</i>)</h3><p>Creates an image provider that will provide images of the given
<i>type</i>.</p>
<h3 class="fn"><a name="QDeclarativeImageProvider-2" />QDeclarativeImageProvider.__init__ (<i>self</i>, <a href="qdeclarativeimageprovider.html">QDeclarativeImageProvider</a>)</h3><h3 class="fn"><a name="imageType" /><a href="qdeclarativeimageprovider.html#ImageType-enum">ImageType</a> QDeclarativeImageProvider.imageType (<i>self</i>)</h3><p>Returns the image type supported by this provider.</p>
<h3 class="fn"><a name="requestImage" /><a href="qimage.html">QImage</a> QDeclarativeImageProvider.requestImage (<i>self</i>, QString <i>id</i>, <a href="qsize.html">QSize</a> <i>size</i>, <a href="qsize.html">QSize</a> <i>requestedSize</i>)</h3><p>Implement this method to return the image with <i>id</i>. The
default implementation returns an empty image.</p>
<p>The <i>requestedSize</i> corresponds to the <a href="qml-image.html#sourceSize-prop">Image.sourceSize</a> requested by
an Image element. If <i>requestedSize</i> is a valid size, the
image returned should be of that size.</p>
<p>In all cases, <i>size</i> must be set to the original size of
the image. This is used to set the <a href="qml-item.html#width-prop">width</a> and <a href="qml-item.html#height-prop">height</a> of image elements that
should be automatically sized to the loaded image.</p>
<p><b>Note:</b> this method may be called by multiple threads, so
ensure the implementation of this method is reentrant.</p>
<h3 class="fn"><a name="requestPixmap" /><a href="qpixmap.html">QPixmap</a> QDeclarativeImageProvider.requestPixmap (<i>self</i>, QString <i>id</i>, <a href="qsize.html">QSize</a> <i>size</i>, <a href="qsize.html">QSize</a> <i>requestedSize</i>)</h3><p>Implement this method to return the pixmap with <i>id</i>. The
default implementation returns an empty pixmap.</p>
<p>The <i>requestedSize</i> corresponds to the <a href="qml-image.html#sourceSize-prop">Image.sourceSize</a> requested by
an Image element. If <i>requestedSize</i> is a valid size, the
image returned should be of that size.</p>
<p>In all cases, <i>size</i> must be set to the original size of
the image. This is used to set the <a href="qml-item.html#width-prop">width</a> and <a href="qml-item.html#height-prop">height</a> of image elements that
should be automatically sized to the loaded image.</p>
<address><hr /><div align="center"><table border="0" cellspacing="0" width="100%"><tr class="address"><td align="left" width="25%">PyQt 4.8.3 for X11</td><td align="center" width="50%">Copyright © <a href="http://www.riverbankcomputing.com">Riverbank Computing Ltd</a> and <a href="http://www.qtsoftware.com">Nokia</a> 2011</td><td align="right" width="25%">Qt 4.7.1</td></tr></table></div></address></body></html>
