title: How wide is my TextBlock after creating it?
body: <p>I use a ListBox in a C#, WPF project. It works. Then I Tried to give the ListBox Items a individual Background. I failed. Now I make a <code>TextBlock</code> first, give them a individual Background and then I put it into the ListBox. It works fine but my problem is that every single line in the Listbox have their own width. I would like have that every ListBox Item has the same largest width. I tried to ask for the width when i created the TextBlock but at this time the <code>width=NaN</code> and the <code>actualWidth=0</code>.</p>
  
  <p>I tried to read all ListBox Items widths with a <code>Button Click</code> Event and it worked.</p>
  
  <p>What do i have to do so that I can do it in the same function as I filled the ListBox?</p>
  
  <p>I would like that every Listbox has the same largest width.
  At this Point each ListBox Item has its own width depending on the text.</p>