NSTextView non-editable in NSSplitview

Question

I have an NSSplitView in My window. the left is an NSOutlineView. When I click the OutlineView's item, the right Which is a custom ViewController's view will look like the below：

Screenshot:

then，a problem occurs that the two NSTextView can't editable while editing the textview. however，I have make it possible to edit it.

Screenshot:

Am I missing anything? Any hint in the right direction is highly appreciated.

Thanks

This is my demo code:github.com/ljz2012008/TestN.git