WPF C# binding textbox to DataGrid

I have this working. However, the data doesn't show up initially in the text box. The first click highlights the textbox. The second click shows the data and the 3rd click puts it in edit mode.

What property do I use to fill the data in initially?

Does it alway take 3 clicks to get into edit mode? Is this how it works or are there different user options?

Thanks.

Sutton