Windows 8開發入門（五）彈出提示框MessageDialog與await、async關鍵字

在以前Silverlight、WPF中的彈出窗口提示中是MessageBox類中進行顯示的，現在Windows 8中使用 Windows.UI.Popups命名空間下的MessageDialog類代替MessageBox。

MessageDialog類有以下常用方法 和屬性:

ShowAsync():異步彈出消息框.

Commands:添加命令,在彈出框界面上同步添加相應的按 鈕.

DefaultCommandIndex:設置默認按鈕的索引,按ENTER鍵將激活該索引對應的命令按鈕

CancelCommandIndex:設置取消退出按鈕的索引,按ESC鍵將激活該索引對應的命令按鈕

Title: 彈出消息框的標題

async:用於方法申明時，此關鍵字是告訴編譯器在這個方法體內可能會有await關鍵 字。

await:用於異步操作時的模擬同步等待，聲明有此關鍵字的異步操作需等待異步操作完成之後才 繼續往下運行，但是不會阻塞UI線程。

注意：使用await關鍵字的方法體，必須使用async聲明方法

現在我們通過一個實例來看MessageDialog、async、await：

<Grid 

Background="{StaticResource ApplicationPageBackgroundThemeBrush}">   
        <Button Content="First Msg" HorizontalAlignment="Left"
                Margin="430,196,0,0" VerticalAlignment="Top"
                Height="51" Width="114" Click="First_Click"/>   
        <Button Content="Secend Msg" HorizontalAlignment="Left"
            Margin="606,196,0,0" VerticalAlignment="Top"
            Height="51" Width="114" Click="Secend_Click"/>   
        <Button Content="Third Msg" HorizontalAlignment="Left"
            Margin="788,196,0,0" VerticalAlignment="Top"
            Height="51" Width="114" Click="Third_Click"/>   
        <Button Content="Fourth Msg" HorizontalAlignment="Left"
            Margin="975,196,0,0" VerticalAlignment="Top"
            Height="51" Width="114" Click="Fourth_Click"/>   
        <TextBlock HorizontalAlignment="Left" Name="tbText"
                   Margin="573,160,0,0" TextWrapping="Wrap"
                   Text="TextBlock" VerticalAlignment="Top"
                   Height="31" Width="565" FontSize="16"/>   
    </Grid>

一:最簡單的MessageDialog

private async void First_Click(object 

sender, RoutedEventArgs e)   
{   
    MessageDialog msg = new MessageDialog("Hello World!這是第一個提示.");   
    msg.Title = "提示1";   
    var msginfo = await msg.ShowAsync();   
}

二:自定義命令集的消息框

private async void Secend_Click(object sender, 

RoutedEventArgs e)   
        {   
            MessageDialog msg1 = new MessageDialog("Hello World!這是第二個提示.");   
            msg1.Title = "提示2";   
            msg1.Commands.Add(new UICommand("確定", command =>   
            {   
                this.tbText.Text = "你點擊了確定按鈕,第二組提示";   
            }));   
            msg1.Commands.Add(new UICommand("取消", command =>   
            {   
                this.tbText.Text = "你點擊了取消按鈕,第二組提示";   
            }));   
            var msg1info = await msg1.ShowAsync();   
        }

三:使用await模擬同步方式得到當前使用命令ID運行響應的代碼段

private 

async void Third_Click(object sender, RoutedEventArgs e)   
        {   
            MessageDialog msg1 = new MessageDialog("Hello World!這是第三個提示.");   
            msg1.Title = "提示3";   
            msg1.Commands.Add(new UICommand("確定", null, 0));   
            msg1.Commands.Add(new UICommand("取消", null, 1));   
            msg1.DefaultCommandIndex = 0;   
            msg1.CancelCommandIndex = 1;   
            var msg1info = await msg1.ShowAsync();   
            switch (Convert.ToInt32(msg1info.Id))   
            {    
                case 0 :   
                     this.tbText.Text = "你點擊了確定按鈕,第三組提示";break;   
                case 1 :   
                    this.tbText.Text = "你點擊了取消按鈕,第三組提示";break;   
                default:   
                    break;   
            }   
        }

四:將命令方法體單獨出來寫方法體

private async void Fourth_Click(object sender, RoutedEventArgs e)   
        {   
            MessageDialog msg1 = new MessageDialog("Hello World!這是第四個提示.");   
            msg1.Title = "提示3";   
            msg1.Commands.Add(new UICommand("確定", new UICommandInvokedHandler(this.ShowTextEnter)));   
            msg1.Commands.Add(new UICommand("取消", new UICommandInvokedHandler(this.ShowTextCancel)));   
            msg1.DefaultCommandIndex = 0;   
            msg1.CancelCommandIndex = 1;   
            var msg1info = await msg1.ShowAsync();   
        }   
        private void ShowTextEnter(IUICommand command)   
        {   
            this.tbText.Text = "你點擊了確定按鈕,第四組提示";   
        }   
        private void ShowTextCancel(IUICommand command)   
        {   
            this.tbText.Text = "你點擊了取消按鈕,第四組提示";   
        }

最後我們來看運行效果如下圖所示,如需源碼請下載： http://files.cnblogs.com/chengxingliang/Win8Message.zip