The QDesignerCustomWidgetInterface class enables Qt Designer to access and construct custom widgets. More

Inheritance diagram of PySide6.QtDesigner.QDesignerCustomWidgetInterface

Detailed Description

QDesignerCustomWidgetInterface provides a custom widget with an interface. The class contains a set of functions that must be subclassed to return basic information about the widget, such as its class name and the name of its header file. Other functions must be implemented to initialize the plugin when it is loaded, and to construct instances of the custom widget for Qt Designer to use.

When implementing a custom widget you must subclass QDesignerCustomWidgetInterface to expose your widget to Qt Designer. For example, this is the declaration for the plugin used in the Custom Widget Plugin example that enables an analog clock custom widget to be used by Qt Designer:

class AnalogClockPlugin(QObject, QDesignerCustomWidgetInterface):

    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QDesignerCustomWidgetInterface")
# public
    AnalogClockPlugin = explicit(QObject parent = None)
    isContainer = bool()
    isInitialized = bool()
    icon = QIcon()
    domXml = QString()
    group = QString()
    includeFile = QString()
    name = QString()
    toolTip = QString()
    whatsThis = QString()
    createWidget = QWidget(QWidget parent)
    def initialize(core):
# private
    initialized = False()

Note that the only part of the class definition that is specific to this particular custom widget is the class name. In addition, since we are implementing an interface, we must ensure that it’s made known to the meta object system using the Q_INTERFACES() macro. This enables Qt Designer to use the qobject_cast() function to query for supported interfaces using nothing but a QObject pointer.

After Qt Designer loads a custom widget plugin, it calls the interface’s initialize() function to enable it to set up any resources that it may need. This function is called with a QDesignerFormEditorInterface parameter that provides the plugin with a gateway to all of Qt Designer's API.

Qt Designer constructs instances of the custom widget by calling the plugin’s createWidget() function with a suitable parent widget. Plugins must construct and return an instance of a custom widget with the specified parent widget.

Exporting your custom widget plugin to Qt Designer using the Q_PLUGIN_METADATA() macro. For example, if a library called libcustomwidgetplugin.so (on Unix) or libcustomwidget.dll (on Windows) contains a widget class called MyCustomWidget, we can export it by adding the following line to the file containing the plugin header:

Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QDesignerCustomWidgetInterface")

This macro ensures that Qt Designer can access and construct the custom widget. Without this macro, there is no way for Qt Designer to use it.

When implementing a custom widget plugin, you build it as a separate library. If you want to include several custom widget plugins in the same library, you must in addition subclass QDesignerCustomWidgetCollectionInterface .


If your custom widget plugin contains QVariant properties, be aware that only the following types are supported:

For a complete example using the QDesignerCustomWidgetInterface class, see the Custom Widget Example . The example shows how to create a custom widget plugin for Qt Designer.

See also

QDesignerCustomWidgetCollectionInterface Creating Custom Widgets for Qt Designer

class PySide6.QtDesigner.QDesignerCustomWidgetInterface
Return type


This function is reserved for future use by Qt Designer.



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Returns a new instance of the custom widget, with the given parent.

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Returns the XML that is used to describe the custom widget’s properties to Qt Designer.

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Returns the name of the group to which the custom widget belongs.

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Returns the icon used to represent the custom widget in Qt Designer's widget box.

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Returns the path to the include file that uic uses when creating code for the custom widget.



Initializes the widget for use with the specified formEditor interface.

See also


Return type


Returns true if the custom widget is intended to be used as a container; otherwise returns false.

Most custom widgets are not used to hold other widgets, so their implementations of this function will return false, but custom containers will return true to ensure that they behave correctly in Qt Designer.

Return type


Returns true if the widget has been initialized; otherwise returns false.

See also


Return type


Returns the class name of the custom widget supplied by the interface.

The name returned must be identical to the class name used for the custom widget.

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Returns a short description of the widget that can be used by Qt Designer in a tool tip.

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Returns a description of the widget that can be used by Qt Designer in “What’s This?” help for the widget.