Why Ctrl+A not working in QListWidget?

Why Ctrl+A not working in QListWidget ?

does it should? you should implement this feature by yourself.

How to implement select all features using Ctrl+A ?

create a shortcut or an action (or install event filter on QListWidget or subclass QListWidget and reimplement keyPressEvent), then connect signal of the shortcut/action with QAbstractItemView::selectAll.

It is solved I added
contextMenuEvent
and slot.

Now Select All is working, but copy not working.
what is the method to copy all selected item from QListWidget?

there is no such method, you have to write it and paste too. ;)