About Layout...

[Patrick Sorcery]

Well, here's the problem: I put a QTreeWidget and a QVTKWidget in a Horizontal Layout, but then the QVTKWidget was huddled to a line, and the whole layout was filled with QTreeWidget

So how to change the widgets' size in the Layout?

[wysota]

Change horizontal size policies of the two widgets or set a minimum size for the QVTKWidget.

[Patrick Sorcery]

Thank you~ solved by changing the size options. Though I still don't know the meaning of those options in 'Policy' (I only know 'Fixed' is to lock the size)

[wysota]

It is all explained in the docs.