我正在编写一个图书馆,意图在桌面(.Net 4.0及更高版本),手机(WP 7.5及以上版本)和
Windows Store(Windows 8及更高版本)应用程序中使用它.
该库能够使用Portable HttpClient库从Internet下载文件,并报告下载进度.
解决方法
我编写了以下代码来实现进度报告.代码支持我想要的所有平台;但是,您需要引用以下NuGet包：
> Microsoft.Net.Http
> Microsoft.Bcl.Async
这是代码：
public async Task DownloadFileAsync(string url,IProgress<double> progress,CancellationToken token)
{
var response = await client.GetAsync(url,HttpCompletionOption.ResponseHeadersRead,token);
if (!response.IsSuccessStatusCode)
{
throw new Exception(string.Format("The request returned with HTTP status code {0}",response.StatusCode));
}
var total = response.Content.Headers.ContentLength.HasValue ? response.Content.Headers.ContentLength.Value : -1L;
var canReportProgress = total != -1 && progress != null;
using (var stream = await response.Content.ReadAsStreamAsync())
{
var totalRead = 0L;
var buffer = new byte[4096];
var isMoreToRead = true;
do
{
token.ThrowIfCancellationRequested();
var read = await stream.ReadAsync(buffer,buffer.Length,token);
if (read == 0)
{
isMoreToRead = false;
}
else
{
var data = new byte[read];
buffer.ToList().CopyTo(0,data,read);
// TODO: put here the code to write the file to disk
totalRead += read;
if (canReportProgress)
{
progress.Report((totalRead * 1d) / (total * 1d) * 100);
}
}
} while (isMoreToRead);
}
}
使用它很简单：
var progress = new Microsoft.Progress<double>();
progress.ProgressChanged += (sender,value) => System.Console.Write("\r%{0:N0}",value);
var cancellationToken = new CancellationTokenSource();
await DownloadFileAsync("http://www.dotpdn.com/files/Paint.NET.3.5.11.Install.zip",progress,cancellationToken.Token);