title: Binding ComboBox item to string
body: <p>I want to bind a ComboBox item to a string, but it does not work. My code is below.</p>
  
  <p>Code in view:</p>
  
  <pre><code>&lt;ComboBox          
   SelectedValuePath="content" 
   SelectedItem="{Binding ProductName}" 
              ......                       
   &lt;ComboBoxItem&gt;1111111111&lt;/ComboBoxItem&gt;
   &lt;ComboBoxItem&gt;2222222222222&lt;/ComboBoxItem&gt;
   &lt;ComboBoxItem&gt;333333333333&lt;/ComboBoxItem&gt;
  &lt;/ComboBox&gt;
  </code></pre>
  
  <p>Code in view model:</p>
  
  <pre><code>private string _productName;
  public string ProductName
  {
      get { return _productName; }
      set
      {
          if (_productName != value)
          {
              _productName = value;
              RaisePropertyChangedEvent("ProductName");
          }
      } 
  }
  </code></pre>