Undo/Redo fails if switching to different SuperNode

[bkiefer]

This could be fixed by clearing the UndoManager, but maybe that's not what's desired.

[aWelker]

Alternatively: Each SuperNode could maintain its own UndoManager. This would allow to switch between different parts of the graph and always be able to undo changes you did to the current environment

[bkiefer]

To reproduce:

• Create supernode, change into supernode, undo: NullPointerException
• Create supernode, change into supernode, create node, change to parent, undo, undo --> node created in new supernode is now in parent

[bkiefer]

Possible solutions:

1. separate Undo managers for all active super nodes
   • When the supernode stack is "popped", the undo managers for the respective supernodes are dropped or not?
   • That would mean that you can only undo things in the current supernode
2. The actions get a SuperNode field and act on the right model.
   • Issue a warning if undoing/redoing things outside the current view!?
3. Changing the SuperNode clears the undo/redo manager. This might be an interim solution until there is a better one

[bkiefer]

Possible solutions:

1. separate Undo managers for all active super nodes
   • When the supernode stack is "popped", the undo managers for the respective supernodes are dropped or not?
   • That would mean that you can only undo things in the current supernode
2. The actions get a SuperNode field and act on the right model.
   • Issue a warning if undoing/redoing things outside the current view!?
3. Changing the SuperNode clears the undo/redo manager. This might be an interim solution until there is a better one

[bkiefer]

fixed by 5d979d7