用http協議來下載網絡上的文件，通常我們需要獲取文件文件的下載進度和下載的速度來給用戶等待過程的一個交代，那么在Windows Phone 7下可以使用WebClient類來實現這一功能，HttpWebRequest類也可以用于下載網絡上的文件，不過HttpWebRequest類不能夠直接地獲取你http請求的完成情況。

使用WebClient.DownloadProgressChanged事件來異步獲取http協議下載文件的進度情況，使用WebClient.DownloadStringCompleted事件來判斷文件的下載是否完成。

<phone:PhoneApplicationPage   
    x:Class="DownLoadTest.MainPage" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone" 
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768" 
    FontFamily="{StaticResource PhoneFontFamilyNormal}" 
    FontSize="{StaticResource PhoneFontSizeNormal}" 
    Foreground="{StaticResource PhoneForegroundBrush}" 
    SupportedOrientations="Portrait" Orientation="Portrait" 
    shell:SystemTray.IsVisible="True"> 
 
    <Grid x:Name="LayoutRoot" Background="Transparent"> 
        <Grid.RowDefinitions> 
            <RowDefinition Height="Auto"/> 
            <RowDefinition Height="*"/> 
        </Grid.RowDefinitions> 
          
        <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28"> 
            <TextBlock x:Name="ApplicationTitle" Text="MY APPLICATION" Style="{StaticResource PhoneTextNormalStyle}"/> 
            <TextBlock x:Name="PageTitle" Text="下載進度顯示" Margin="9,-7,0,0" Style="{StaticResource PhoneTextTitle1Style}"/> 
        </StackPanel> 
 
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0"> 
            <Grid.RowDefinitions> 
                <RowDefinition Height="114*"/> 
                <RowDefinition Height="493*"/> 
            </Grid.RowDefinitions> 
            <ProgressBar Foreground="Green" Height="30" HorizontalAlignment="Left" Margin="9,79,0,0" Name="progressBar1" VerticalAlignment="Top" Width="377" Value="0" Maximum="100" FontSize="72" BorderThickness="0"/> 
            <TextBlock Height="53" Margin="12,20,-16,0" Name="textBox1" Text="正在下載文件 . . ." VerticalAlignment="Top" Width="460"/> 
            <TextBlock Margin="6,24,287,427" Name="result" Text="下載的速度:  " Grid.Row="1"/> 
            <TextBlock  Foreground="White" Height="59" HorizontalAlignment="Left" Margin="203,13,0,0" Name="textBox2" Text=""  VerticalAlignment="Top" Width="123"/> 
            <Button Content="測試下載" Height="72" HorizontalAlignment="Left" Margin="96,244,0,0" Name="button1" VerticalAlignment="Top" Width="199" Click="button1_Click" Grid.Row="1"/> 
            <TextBlock Height="59"  Margin="2,101,254,0" Name="finalresult" Text="平均的下載速度:  " VerticalAlignment="Top" Grid.Row="1"/> 
            <TextBlock Height="57" HorizontalAlignment="Left" Margin="174,89,0,0" Name="textBlock1" Text="" VerticalAlignment="Top" Width="156" Grid.Row="1"/> 
            <TextBlock Height="47" HorizontalAlignment="Left" Margin="12,166,0,0" Name="textBlock2" Text="文件的大小：" VerticalAlignment="Top" Width="127" Grid.Row="1"/> 
            <TextBlock Height="47" HorizontalAlignment="Right" Margin="0,166,190,0" Name="textBlock3" Text="" VerticalAlignment="Top" Grid.Row="1" Width="121"/> 
            <TextBlock Height="47" HorizontalAlignment="Right" Margin="0,19,190,0" Name="textBlock4" Text="" VerticalAlignment="Top" Grid.Row="1" Width="134"/> 
        </Grid> 
    </Grid> 
</phone:PhoneApplicationPage> 

using System;  
using System.Net;  
using System.Windows;  
using Microsoft.Phone.Controls;  
using System.Diagnostics;  
 
namespace DownLoadTest  
{  
    public partial class MainPage : PhoneApplicationPage  
    {  
        private long siz;  
        private long speed;  
        private Stopwatch sw;  
        private Stopwatch sw1;  
 
        public MainPage()  
        {  
            InitializeComponent();  
        }  
 
        private void button1_Click(object sender, RoutedEventArgs e)  
        {  
            testspeed();  
        }  
 
        public void testspeed()  
        {  
            WebClient client = new WebClient();  
            progressBar1.Value = 0.0;  
            textBox2.Text = "0 %";  
            client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(this.webClient_DownloadStringCompleted);  
            client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(this.webClient_DownloadProgressChanged);  
            sw = Stopwatch.StartNew();//用來記錄總的下載時間  
            sw1 = Stopwatch.StartNew();//用來記錄下載過程中的時間片，用于計算臨時速度  
            client.DownloadStringAsync(new Uri("http://dl_dir.qq.com/qqfile/qq/QQ2011/QQ2011.exe"));  
        }  
        //下載過程事件  
        public void webClient_DownloadProgressChanged(object s, DownloadProgressChangedEventArgs e)  
        {  
            textBox2.Text = e.ProgressPercentage.ToString() + " %";  
            sw1.Stop();  
            long num = e.BytesReceived / 1024;  
            if (sw1.Elapsed.Seconds != 0)  
            {  
                speed = num / ((long)sw1.Elapsed.Seconds);  
            }  
            textBlock4.Text = this.speed + " KB/sec";  
            progressBar1.Value = e.ProgressPercentage;  
            siz = e.TotalBytesToReceive;  
            textBlock3.Text = siz + "KB";  
            sw1.Start();  
        }  
        //下載完成事件  
        public void webClient_DownloadStringCompleted(object s, DownloadStringCompletedEventArgs e)  
        {  
            sw.Stop();  
            sizsiz = siz/1024;  
            long num = siz / ((long)sw.Elapsed.Seconds);  
            sw.Reset();  
            textBox1.Text = "下載完成！";  
            textBlock1.Text = num + " KBytes/sec";  
        }  
    }  
} 

原文鏈接：http://www.cnblogs.com/linzheng/archive/2011/11/03/2234971.html