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I've got a MVVM-like situation (not using any frameworks) where I have a main window with a toolbar and a documents area. The documents have command bindings (e.g. Undo and Redo). When the keyboard focus is outside of the document, it doesn't know how to execute any of the commands, so the buttons become disabled.

What I would like to do is add a mechanism whereby the main window will forward commands to the active document (if it has one). Using CommandManager.AddPreviewCanExecuteHandler I can get the events in the main window, but I can't figure out how to send them on to the child document- I tried e.CanExecute = e.Command.CanExecute(CurrentDocument), but that just ends up re-calling the PreviewCanExecuteHandler again, and the child's CanExecute handler isn't called.

How can I send an arbitrary ICommand to a child control?

arolson101
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2 Answers2

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The answer is here- call CurrentDocument.RaiseEvent(e), making sure to do it via a handler registered with CommandManager.AddCanExecuteHandler (not AddPreviewCanExecuteHandler). And make sure to check for infinite recursion.

Community
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arolson101
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  • +1 Worked like a charm... Though be aware that the event might bubble and thus return to the parent... I fixed this by setting a boolean variable whenever I am redirecting a command. – reSPAWNed Apr 26 '12 at 11:01
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Presumably, you have some mechanism of managing active documents -- enumerating them, identifying the active document, etc.

I suggest that instead of thinking about taking commands from the main window and forwarding them to the document, think of it as taking the commands available on the active document and attaching them to the main window.

Whatever is your common interface among documents, add some properties:

ICommand Undo { get; }
ICommand Redo { get; }

Now you'll bind your main window's controls to ActiveDocument.Undo and ActiveDocument.Redo, where ActiveDocument is a property in your main window viewmodel. When ActiveDocument changes, you'll get a property change notification so the buttons can become enabled/disabled accordingly.

Incidentally, when I've done similar, I expose some composite object of which the ICommands are properties, but with separate CanUndo/CanRedo boolean properties and other metadata -- that gives me a nicer abstraction by which to control enabling and disabling based on the state of the commands stacks.

Jay
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  • couple questions: (1) does this mean I can't use `ApplicationCommands.Undo`? (2) how would you set up `ActiveDocument.Undo` so that it applies to only the document? – arolson101 Dec 02 '11 at 15:42
  • @arolson101 I am sure there is a way to wire things together with ApplicationCommands.Undo, but I can't speak to that as my experience with it is limited. `ActiveDocument.Undo` would apply only to the document insofar as `ActiveDocument` would refer only to the one active document, if any. – Jay Dec 02 '11 at 16:07
  • This might be the only solution, but it seems to be just as much work to bind the commands to the buttons as it would be to forward each command to the active document; also, I want to conditionally forward to either a document or a projects pane, depending on where keyboard focus is – arolson101 Dec 05 '11 at 15:42