Floating Window Group does not hide correctly

[Dirkster99]

Issue

A Floating Window (Group with at least 2 tool windows) does not hide correctly.

The framework hides only the toolwindows but leaves floating window empty.
There is a NullReference Exception + Crash when user tries to drag the flowting tool window.

Steps to verify (using the MLib_Test client)

1. Drag 2 tool windows (LayoutAnchorable) into one floating window
   

2. Close MLib_Test Application to Save the Layout

3. Restart MLib_Test Application to Reload the Layout

4. Click Hide (button) of the floating window
   

Bug

• The empty floating window is still visible
• Dragging the empty floating window leads to a crash
  AvalonDock.Layout.txt

Crash is reproducable with this layout but somehow not with above steps anymore(?):

[Dirkster99]

A possible solution is documented in FloatingWindowGroup branch.

This commit changes the:

1. LayoutAnchorableFloatingWindowControl.OnExecuteHideWindowCommand() by adding a Hide() call to hide the FloatingToolWindows

2. To bring the hidden element back would require a re-start of the application unless the second addition is implemented in LayoutAnchorable.UpdateParentVisibility():

      // Element is Hidden since it has no parent but a previous parent
      if (this.PreviousContainer != null && Parent == null)
      {
        // Go back to using previous parent
        Parent = PreviousContainer;
        PreviousContainer = null;
      }

This code makes the Tool Window re-appear in the MainWindow when the user tries to unhide it after hidding the FloatingWIndow.

[Dirkster99]

I've tested a little bit with floating windows and found a workflow that was not working OK as a result of the first fix candidate:

0. Clean_All.bat

1. Load project in VS and rebuild

2. Start MLib_Test

3. Drag all Tool Windows by the title bar into floating state

4. Close the floating window with Hide (x) button

5. Exit application (layout is saved)

6. Re-start application (layout is loaded)
   Bug:
   The hidden Toolwindows cannot be re-shown with Tools>tool window toggle

The cause of this new issue seems to be the PreviousContainer = null; statement in LayoutAnchorable.UpdateParentVisibility() so I removed it with this commit and can no longer reproduce the new issue while the fix continues to work :-)

So, just for clarities sake - the current idea on the fix is this change:

1. LayoutAnchorableFloatingWindowControl.OnExecuteHideWindowCommand() by adding a Hide() call to hide the FloatingToolWindows

2. To bring the hidden element back would require a re-start of the application unless the second addition is implemented in LayoutAnchorable.UpdateParentVisibility():

      // Element is Hidden since it has no parent but a previous parent
      if (this.PreviousContainer != null && Parent == null)
      {
        // Go back to using previous parent
        Parent = PreviousContainer;
      }

This code makes the Tool Window re-appear in the MainWindow when the user tries to unhide it after hidding the FloatingWIndow.