继承 QObject and QDesignerCustomWidgetCollectionInterface .
The QPyDesignerCustomWidgetCollectionPlugin 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 several custom widgets you should implement a Python class derived from QPyDesignerCustomWidgetCollectionPlugin rather than one derived from QObject and QDesignerCustomWidgetCollectionInterface .
parent argument, if not None, causes self to be owned by Qt instead of PyQt.