This signal is emitted when the user presses a mouse button inside the widget.
The specified item is the item that was clicked, or 0 if no item was clicked. The column is the item's column that was clicked, or -1 if no item was clicked
帮助上是这么写的。
当没有点到的时候,item为0,column为-1
现在很郁闷,想得到一个点击QTreeWidget空白处的信号,好像没有啊