windows 8.1 MessageDialog

    private Popup p;
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            p=new Popup();
            DengluDemo dl=new DengluDemo();
            dl.Width = 1366;
            dl.Height = 260;
            dl.Margin = new Thickness(0, 200, 0, 0);
            //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) =>
            {
                
            }, 0));
            md.Commands.Add(new UICommand("取消", (a) =>
            {

            }, 1));
            md.DefaultCommandIndex = 0;
            md.CancelCommandIndex = 1;
            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);
            }
        }