title: I can't update my binding data(only update at first time)
body: <p>I want to show the stream data to textbox in real time. But the textbox doesn't updated even  the stream data has updated. I don't know what is wrong.</p>
  <p>Here is my XAML code.</p>
  <pre><code>&lt;TextBox Text=&quot;{Binding Path = marketPrice}&quot; HorizontalAlignment=&quot;Left&quot;/&gt;
  </code></pre>
  <p>And this is View Model code.</p>
  <pre><code>public class OrderTestViewModel : INotifyPropertyChanged
  {
       public QuotesDataSource DataSource;
       public string _marketPrice =&gt; DataSource.SymbolPrice;
       public string marketPrice
       {
           get { return _marketPrice; }
           set
           {
               RaisePropertyChanged(&quot;marketPrice&quot;);
           }
       }  
       public event PropertyChangedEventHandler PropertyChanged;
       public void RaisePropertyChanged(string propertyName)
       {
           if (PropertyChanged != null)
               PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
       }   
  }
  </code></pre>
  <p>I checked the marketPrice is updated real time.</p>
  <p>And the last is hidden code.</p>
  <pre><code>public partial class OrderTest : UserControl
  {
     OrderTestViewModel model = new OrderTestViewModel();
     public OrderTest()
     {
         InitializeComponent();
         DataContext = model;
     }
  }
  </code></pre>
  <p>Please help me.</p>