title: TextBox value not updating on Button click
body: <p>This is my XAML code:</p>
  <pre class="lang-xml prettyprint-override"><code>&lt;TextBox Grid.Row=&quot;2&quot; Grid.Column=&quot;1&quot; HorizontalAlignment=&quot;Left&quot; VerticalAlignment=&quot;Center&quot; Width=&quot;25&quot; Margin=&quot;100,0,0,0&quot; Height=&quot;25&quot; Text=&quot;{Binding Quantity, UpdateSourceTrigger=PropertyChanged}&quot;&gt;&lt;/TextBox&gt;
  &lt;Button Grid.Row=&quot;2&quot; Grid.Column=&quot;1&quot; HorizontalAlignment=&quot;Center&quot; VerticalAlignment=&quot;Center&quot; Width=&quot;100&quot; Height=&quot;25&quot; Content=&quot;+&quot; Command=&quot;{Binding AddCommand}&quot;&gt;&lt;/Button&gt;
  &lt;Button Grid.Row=&quot;2&quot; Grid.Column=&quot;1&quot; HorizontalAlignment=&quot;Right&quot; Margin=&quot;10&quot; VerticalAlignment=&quot;Center&quot; Width=&quot;100&quot; Height=&quot;25&quot; Content=&quot;-&quot; Command=&quot;{Binding SubtractCommand}&quot;&gt;&lt;/Button&gt;
  </code></pre>
  <p>This is my C# code:</p>
  <pre class="lang-cs prettyprint-override"><code>public class ViewModel : ObservableObject, INotifyPropertyChanged
  {
      private int quantity = 0;
      public int Quantity
      {
          get =&gt; quantity;
          set
          {
              if (quantity == value) return;
              quantity = value;
              this.RaisePropertyChangedEvent(nameof(Quantity));
          }
      }
      public ICommand AddCommand =&gt; new RelayCommand&lt;string&gt;(
          Add,
          x =&gt; true
      );
      public ICommand SubtractCommand =&gt; new RelayCommand&lt;string&gt;(
          Sub,
          x =&gt; true
      );
      private void Add(string obj)
      {
          quantity += 1;
          Debug.WriteLine(quantity);
      }
      private void Sub(string obj)
      {
          quantity -= 1;
          Debug.WriteLine(quantity);
      }
  }
  </code></pre>
  <p>If you press the +/- buttons, the value of <code>quantity</code> changes. The output of <code>Debug.Writeline</code> is the correct result. The problem is that the text of the TextBox is not updated on Button click.</p>