title: Silverlight combobox number of items shown refresh
body: <p>I have two combo boxes on a SL page. When Combo 1 updates, a service is called and populates Combo 2. </p>
  
  <p>On the first call, 3 results are returned. When the combo box is expanded, you can see all 3 options.</p>
  
  <p>On the second call, 4 results are returned. When the combo box is expanded, you can see 3 options, with a vertical scroll bar.</p>
  
  <p>If I reload and do those steps in reverse, I get 4 rows the first call and 3 rows + a blank row on the second call. (No, the blank is not a record. It cannot be selected.)</p>
  
  <p>It appears that the drop down list size keeps the first generated height.</p>
  
  <p>How can I refresh the combo box max items shown after each service call?</p>
  
  <p>Thanks!</p>
  
  <p><strong>Edit #1</strong></p>
  
  <p>The code follows the M-V-VM pattern. When the page loads, the <code>Group1</code> populates the first combo box, and nothing is selected. When the user makes a selection, that selection is bound to Group1Selection.</p>
  
  <pre><code>&lt;ComboBox ItemsSource="{Binding Path=Group1}" SelectedItem="{Binding Path=Group1Selection}" /&gt;
  &lt;ComboBox ItemsSource="{Binding Path=Group2}" SelectedItem="{Binding Path=Group2Selection}" /&gt;
  </code></pre>
  
  <p>In the viewmodel, in the set accessor of the <code>Group1Selection</code> property, I have something like</p>
  
  <pre><code>set
  {
      if (group1Selection != value)
      {
          group1Selection = value;
          PopulateGroup2();
          OnPropertyChanged("Group1Selection");
      }
  }
  </code></pre>
  
  <p>Where PopulateGroup2 performs my service call async, gets the data, and puts that data into the exposed property of <code>Group2</code>.</p>
  
  <p>Under "normal" conditions, this isn't a problem, since most options have dozens of possible selections. However, a couple of the <code>Group1</code> choices only have 3 or 4 child choices. If one of those is selected first, then the height of the ComboBox, for the rest of that application instance is set to 3 or 4, respectively, instead of maxing out at 8 shown items.</p>
  
  <p>Following the M-V-VM pattern, there is no code in the code-behind.</p>