继承 QObject and QDesignerCustomWidgetInterface .
The QPyDesignerCustomWidgetPlugin class is provided to work around the fact that it is not possible for a Python class to derive from multiple Qt 类。
In order to write a plugin that contains a single custom widget you should implement a Python class derived from QPyDesignerCustomWidgetPlugin rather than one derived from QObject and QDesignerCustomWidgetInterface .
parent argument, if not None, causes self to be owned by Qt instead of PyQt.