title: WPF ItemsControl vs contentControl question
body: <p>hopefully some WPF ninja can explain to me why if I have a tab control and in my tab I put content (in this case a user control) into a ItemsControl or ContentControl the content in the contentControl will expand and fill up the whole screen but if it is in an items control it will not... I think the example will make this more clear. </p>
  
  <pre><code> public MainWindow()
  {
    InitializeComponent();
  
    //This content won't expand to fill the available space
    var t1 = new TabItem();
    t1.Header = "Tab One";
    var ic = new ItemsControl();
    ic.Items.Add(new UserControl1());
    t1.Content = ic;
  
    //in this case the label will fill up the whole window...
    var t2 = new TabItem();
    t2.Header = "Tab Two";
    var c = new ContentControl();
    c.Content = new UserControl1();
    t2.Content = c;
  
    MyTab.Items.Add(t1);
    MyTab.Items.Add(t2);
  }
  </code></pre>
  
  <p>here is the XAML for the window. </p>
  
  <pre><code> &lt;Grid&gt;
      &lt;TabControl Name="MyTab"&gt;
  
      &lt;/TabControl&gt;
  &lt;/Grid&gt;
  </code></pre>
  
  <p>Here is the user control - nothing but a label... </p>
  
  <pre><code>&lt;UserControl x:Class="TabControlTest.UserControl1"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
           xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
           xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
           mc:Ignorable="d" 
           d:DesignHeight="300" d:DesignWidth="300" Background="Red"&gt;
  &lt;Label Content="User control one"/&gt;
  </code></pre>
  
  <p></p>
  
  <p>Thanks!!!</p>