wp8通过WebClient从服务器下载文件

通过WebClient从Web服务器下载文件，并保存到wp8手机应用程序的独立存储。

我们可以通过利用webClient_DownloadStringCompleted来获得下载完成所需要的时间，用Stopwatch得到下载的总时间。

通常我们都将上传、下载作为异步事件来处理，以便不阻止主线程。

String url = "http://172.18.144.248:8080/upload/" + filename;
WebClient client = new WebClient();
client.Encoding = System.Text.Encoding.UTF8;
client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(this.webClient_DownloadStringCompleted);
Stopwatch sw;
sw = Stopwatch.StartNew();//用来记录总的下载时间

public static Task<string> DownloadStringTask(this WebClient webClient, Uri uri)
{
var tcs = new TaskCompletionSource<string>();
webClient.DownloadStringCompleted += (s, e) =>
{
if (e.Error != null)
{
tcs.SetException(e.Error);
}
else
{
tcs.SetResult(e.Result);
}
};
webClient.DownloadStringAsync(uri);
return tcs.Task;
}

public void webClient_DownloadStringCompleted(object s, DownloadStringCompletedEventArgs e)
{
sw.Stop();
long totaltime = sw.ElapsedMilliseconds;
MessageBox.Show(totaltime+"ms,download succeed!");
}

webClient.DownloadStringAsync(uri)得到的是字符串，我们将其保存到独立存储中，通过 await IsolatedStorageHelper.writeFileAsync(filename,cont)异步执行，通过writeFileAsync函数写入独立存储。

public async static Task writeFileAsync(String fileName, String text)
{
using (IsolatedStorageFile isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
{
if (isolatedStorageFile.FileExists(fileName))
{
isolatedStorageFile.DeleteFile(fileName);
}
using (IsolatedStorageFileStream isolatedStorageFileStream = isolatedStorageFile.CreateFile(fileName))
{
using (StreamWriter streamWriter = new StreamWriter(isolatedStorageFileStream,System.Text.Encoding.UTF8))
{
streamWriter.Write(text);
streamWriter.Close();
}
isolatedStorageFileStream.Close();
isolatedStorageFileStream.Dispose();

}
}
}