title: Bind Multibinding Textbox in WPF MVVM
body: <p>I have 3 TextBoxes bind with my class(<strong><em>Transaction</em></strong>) properties like this</p>
  
  <pre><code>&lt;TextBox Text="{Binding Path=Transaction.Bills100,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Name="bills100" Grid.Column="2" Grid.Row="1" Margin="7"&gt;&lt;/TextBox&gt;
  &lt;TextBox Text="{Binding Path=Transaction.Bill50,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Name="bills50" Grid.Column="2" Grid.Row="2" Margin="7"&gt;&lt;/TextBox&gt;
  &lt;TextBox Text="{Binding Path=Transaction.Bill20,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Name="bills20" Grid.Column="2" Grid.Row="3" Margin="7"&gt;&lt;/TextBox&gt;
  </code></pre>
  
  <p>Also I have another TextBox where I have done multibinding and done addition of the first three Textboxes like</p>
  
  <pre><code> &lt;TextBox Grid.Column="2" IsReadOnly="True" Grid.Row="7" Grid.ColumnSpan="2" Margin="7" Name="TotalBills"&gt;
     &lt;TextBox.Text&gt;
          &lt;MultiBinding Converter="{ikriv:MathConverter}" ConverterParameter="x+y+z" Mode="TwoWay"&gt;
              &lt;Binding Path="Text" ElementName="bills100" /&gt;
              &lt;Binding Path="Text" ElementName="bills50" /&gt;
              &lt;Binding Path="Text" ElementName="bills20" /&gt;
           &lt;/MultiBinding&gt;
       &lt;/TextBox.Text&gt;
   &lt;/TextBox&gt;
  </code></pre>
  
  <p>I want to bind this multibinding textbox with my class(<strong><em>Transaction</em></strong>) with property as Transaction.Total like my first three textboxes but it shows error</p>
  
  <blockquote>
    <p>Property text is set more than once</p>
  </blockquote>