WPF: “ApplicationCommands.New” showing incorrect Source in case of MenuItem

Question

I am new to WPF and am going through the examples of Professional WPF in .net 4.5. In the commands chapter, there is an example where multiple controls can send the same command

Answer 1

Yes this is correct (or at least that's how it's designed). Routed commands start routing based on the CommandTarget you specify. If one isn't specified typically the object raising the event uses itself as the starting point (so the MenuItem in this case). So the routing starts with the MenuItem in this case as you might expect. Nothing handles it there so the CommandManager goes up the parent chain. When it hits an element that is a FocusScope (like the Menu), it checks the FocusedElement of the "parent" FocusScope (e.g. the FocusScope of the parent of the Menu which in this case is the Window). If there is a FocusedElement (which there will be one once you have focused an element in the window's focus scope such as your button, checkbox, a textbox that you might put in that stackpanel, etc.) then the CommandManager starts routing the event from that element. When it does that it creates a new ExecutedRoutedEventArgs where the OriginalSource is that starting element (so the button, checkbox, textbox) and then continues routing up the tree.

So when you first ran the app, the FocusedElement of the Window (that's the root focus scope in your example) is null so there is no re-routing needed so the CommandManager just kept going up the parent chain past the Menu and that is why MenuItem appeared as the Source & OriginalSource. When you clicked on the Button you gave that keyboard focus and as part of it also became the logically focused element of its focus scope (i.e. the FocusedElement of its containing FocusScope). So when the MenuItem was subsequently clicked and the CommandManager ultimately reached the Menu, it then re-routed over to the Button (or whatever you focused in the window's focusscope) and started routing up from there. I say this is expected because with routed command you want the routing to go through the logically focused element so that for example, the Cut command of a menu item would trigger a cut of the TextBox in the Window that had focus.