这篇文章是我对ChildWindow的理解，举例说明：

有时候在项目中需要弹出子窗体进行一些操作，然后将操作的值返回到父窗体中。

下图是子窗体的界面（比较粗糙。。。。）

下面贴出其代码：

子窗体前台代码
 <controls:ChildWindow x:Class="FineMmarketing.Controls.SelectChild"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
            Width="365" Height="226"
            Title="请选择纬度">
     <Grid x:Name="LayoutRoot" Margin="2" >
         <Grid.RowDefinitions>
             <RowDefinition />
             <RowDefinition Height="Auto" />
         </Grid.RowDefinitions>
         <StackPanel Margin="0,0,0,37">           
             <TextBlock Width="100" Height="30" Text="请输入纬度：" Margin="83 35 0 0" HorizontalAlignment="Left" />
             <TextBox x:Name="Txt" Width="200" Height="30" HorizontalAlignment="Center" Margin="24 0 0 0"/>
         </StackPanel>
        
         <Button x:Name="CancelButton" Content="取消" Click="CancelButton_Click" Width="75" Height="23" HorizontalAlignment="Right" Margin="0,12,0,0" Grid.Row="1" />
         <Button x:Name="OKButton" Content="确定" Click="OKButton_Click" Width="75" Height="23" HorizontalAlignment="Right" Margin="0,12,79,0" Grid.Row="1" />
     </Grid>
 </controls:ChildWindow>

子窗体后台代码
  /// <summary>
         /// 确定按钮
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>
         private void OKButton_Click(object sender, RoutedEventArgs e)
         {           
             if (!String.IsNullOrEmpty(this.Txt.Text))
             {
                 Regex reg = new Regex("^[0-9]+$");
                 Match ma = reg.Match(this.Txt.Text.ToString());
                 if (ma.Success)
                 {
                     Num = Convert.ToInt32(this.Txt.Text.ToString());
                     if (Num > 10)
                     {
                         MessageBox.Show("纬度不能超过10！");
                         return;
                     }
                     else
                     {
                         this.Tag = Num;
                     }          
                 }
                 else
                 {
                     MessageBox.Show("请输入正确的纬度！");
                 }
             }
             else
             {
                 MessageBox.Show("请输入纬度！");
             }
             this.DialogResult = true;
         }
  /// <summary>
         /// 取消按钮
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>
         private void CancelButton_Click(object sender, RoutedEventArgs e)
         {
             this.DialogResult = false;
         }

然后看一下在父窗体中如何调用子窗体，然后后台定义事件执行子窗体关闭事件。

子窗体后台代码
 SelectChild myChild = new SelectChild();//申明子窗体对象
 ////定义子窗体关闭事件
 myChild.Closed += new EventHandler(win_Closed);
 
 
  /// <summary>
         /// 子窗口关闭返回值事件
         /// </summary>
         /// <param name="sender"></param>
         /// <param name="e"></param>
         void win_Closed(object sender,EventArgs e)
         {
             bool? result = myChild.DialogResult;
             //判断是否是顶级确定按钮关闭并且有返回值
             if (result.HasValue && result.Value)
             {
                 //是定义在子窗体中的公有的全局变量
                 MessageBox.Show(myChild.txt);
             }
         }