How to set focus on newly added document

Hi,

Somewhat new to this so if somebody could point me in the right direction I would appreciate it.

I'm using MVVM along with a TabbedMdiHost and using a DeferableObservableCollection to hold the documents (this.documentItems)

I can successfully add a new document programmatically by adding it to the documentItems collection (this.documentItems.Add(xxxxx)

My question is how do I then set focus to that new document window? I have looked high and low and I'm sure it's simple.

Right now it adds the tab but the focus stays on the current document.

Thanks!

Rick