windows 8.1 MessageDialog

     private Popup p;
         private void Button_Click(object sender, RoutedEventArgs e)
         {
             p=new Popup();
             DengluDemo dl=new DengluDemo();
             dl.Width = ;
             dl.Height = ;
             dl.Margin = new Thickness(, , , );
             //if (p != null || p.IsOpen == true)
             //{
             //    return;
             //}
             MessageDialog md = new MessageDialog("是否退出登陆");
             md.Commands.Add(new UICommand("确定", (a) =>
             {

             }, ));
             md.Commands.Add(new UICommand("取消", (a) =>
             {

             }, ));
             md.DefaultCommandIndex = ;
             md.CancelCommandIndex = ;
             var cmd = md.ShowAsync();
             dl.eh = (a, b) =>
             {
                 p.Child = dl;
                 p.IsOpen = true;
             };
             p.Child = dl;
             p.IsOpen = true;

         }
     }

 <UserControl
     x:Class="vs2013win8._1.DengluDemo"
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:local="using:vs2013win8._1"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
     mc:Ignorable="d"
     d:DesignHeight="260"
     d:DesignWidth="1360">

     <Grid>
         <Grid.Background>
             <SolidColorBrush Color="Black" Opacity="0.7"></SolidColorBrush>
         </Grid.Background>
         <StackPanel Background="LightSeaGreen" Orientation="Vertical" >

             <StackPanel Orientation="Horizontal" Margin="428,40,0,0">
                 <TextBlock Text="用户名:" FontSize="25" Width="80"></TextBlock>
                 <TextBox x:Name="txt_Name" Width="273" Margin="20,0,0,0"></TextBox>
             </StackPanel>

             <StackPanel Orientation="Horizontal" Margin="428,40,0,0">
                 <TextBlock Text="密   码:" FontSize="25" Width="80"></TextBlock>
                 <PasswordBox x:Name="txt_Password" Width="273" Margin="20,0,0,0"></PasswordBox>
             </StackPanel>

             <StackPanel Orientation="Horizontal" Margin="428,30,0,0">
                 <HyperlinkButton Tapped="Button_Tapped_3" FontSize="18" Foreground="White">还没有账号 点击去注册</HyperlinkButton>
                 <Button Tapped="Button_Tapped_1" Content="登录" FontSize="20" Foreground="White" Background="LightSeaGreen"  Width="150"  Height="49" Margin="180,0,0,0"/>
                 <Button Tapped="Button_Tapped_2" Content="取消" FontSize="20" Foreground="White" Background="LightSeaGreen"  Width="153"  Height="49" Margin="20,0,0,0"/>
             </StackPanel>
         </StackPanel>
     </Grid>
 </UserControl>

   public EventHandler eh;
         private void Button_Tapped_1(object sender, TappedRoutedEventArgs e)
         {
             if (eh != null)
             {
                 eh(this,null);
             }
         }