1.st部分問題: 這兩個事件註冊有什麼區別?問題的UIElement.AddHandler()vs .Event + =定義
_popUp.AddHandler(PreviewMouseLeftButtonDownEvent, new MouseButtonEventHandler(PopUp_PreviewMouseLeftButtonDown));
_popUp.PreviewMouseLeftButtonDown += new MouseButtonEventHandler(_popUp_PreviewMouseLeftButtonDown);
2.nd部分: 或最終與
popUp.Opened += PopUp_Opened;