New Post: ChildWindow - How to pass a value from a childwindow to a main form

<TextBox x:Name="txtResult"
                  Text="{Binding Text, ElementName=txtUserInput}"
                  BorderThickness="1"
                  BorderBrush="Black"
                  Height="20"
                  Margin="10" />

<xctk:ChildWindow x:Name="_childWindow"
                              WindowBackground="#9A9999"
                              Caption="Modal ChildWindow"
                              IsModal="True"
                              Left="75"
                              Top="50"
                              Width="275"
                              Height="125"
                              WindowState="Open"
                              Closed="_childWindow_Closed_1">
               <TextBox x:Name="txtUserInput"
                        Text=""
                        BorderThickness="1"
                        BorderBrush="Black"
                        Height="20"
                        Margin="10" />
            </xctk:ChildWindow>


private void _childWindow_Closed_1( object sender, EventArgs e )
    {
      txtResult.Text = txtUserInput.Text;
    }