成员的完整列表，这些成员属于 Dtk::Widget::DThumbnailProviderPrivate::ProduceInfo,包括所有继承而来的类成员

callback (定义于 Dtk::Widget::DThumbnailProviderPrivate::ProduceInfo)	Dtk::Widget::DThumbnailProviderPrivate::ProduceInfo
fileInfo (定义于 Dtk::Widget::DThumbnailProviderPrivate::ProduceInfo)	Dtk::Widget::DThumbnailProviderPrivate::ProduceInfo
size (定义于 Dtk::Widget::DThumbnailProviderPrivate::ProduceInfo)	Dtk::Widget::DThumbnailProviderPrivate::ProduceInfo