C# .Net DownloadFileTaskAsync健壮WPF代码
当网络连接丢失3分钟或更长时间时，下面的WPF代码将永久挂起。当连接恢复时，它既不会抛出也不会继续下载，也不会超时。若网络连接丢失的时间较短，比如半分钟，它会在连接恢复后抛出。如何使其更健壮，以在网络中断后生存C# .Net DownloadFileTaskAsync健壮WPF代码,c#,wpf,asynchronous,webclient,C#,Wpf,Asynchronous,Webclient,当网络连接丢失3分钟或更长时间时，下面的WPF代码将永久挂起。当连接恢复时，它既不会抛出也不会继续下载，也不会超时。若网络连接丢失的时间较短，比如半分钟，它会在连接恢复后抛出。如何使其更健壮，以在网络中断后生存 using System; using System.Net; using System.Net.NetworkInformation; using System.Windows; namespace WebClientAsync { public partial class
using System;
using System.Net;
using System.Net.NetworkInformation;
using System.Windows;
namespace WebClientAsync
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
NetworkChange.NetworkAvailabilityChanged +=
(sender, e) => Dispatcher.Invoke(delegate()
{
this.Title = "Network is " + (e.IsAvailable ? " available" : "down");
});
}
const string SRC = "http://ovh.net/files/10Mio.dat";
const string TARGET = @"d:\stuff\10Mio.dat";
private async void btnDownload_Click(object sender, RoutedEventArgs e)
{
btnDownload.IsEnabled = false;
btnDownload.Content = "Downloading " + SRC;
try {
using (var wcl = new WebClient())
{
wcl.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
await wcl.DownloadFileTaskAsync(new Uri(SRC), TARGET);
btnDownload.Content = "Downloaded";
}
}
catch (Exception ex)
{
btnDownload.Content = ex.Message + Environment.NewLine
+ ((ex.InnerException != null) ? ex.InnerException.Message : String.Empty);
}
btnDownload.IsEnabled = true;
}
}
}
DownloadProgressChangedEventHandler计时器using System;
using System.Net;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
namespace WebClientAsync
{
public partial class MainWindow : Window
{
const string SRC = "http://ovh.net/files/10Mio.dat";
const string TARGET = @"d:\stuff\10Mio.dat";
// Time needed to restore network connection
const int TIMEOUT = 30 * 1000;
public MainWindow()
{
InitializeComponent();
}
private async void btnDownload_Click(object sender, RoutedEventArgs e)
{
btnDownload.IsEnabled = false;
btnDownload.Content = "Downloading " + SRC;
CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken token = cts.Token;
Timer timer = new Timer((o) =>
{
// Force async cancellation
cts.Cancel();
}
, null //state
, TIMEOUT
, Timeout.Infinite // once
);
DownloadProgressChangedEventHandler handler = (sa, ea) =>
{
// Restart timer
if (ea.BytesReceived < ea.TotalBytesToReceive && timer != null)
{
timer.Change(TIMEOUT, Timeout.Infinite);
}
};
btnDownload.Content = await DownloadFileTA(token, handler);
// Note ProgressCallback will fire once again after awaited.
timer.Dispose();
btnDownload.IsEnabled = true;
}
private async Task<string> DownloadFileTA(CancellationToken token, DownloadProgressChangedEventHandler handler)
{
string res = null;
WebClient wcl = new WebClient();
wcl.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
wcl.DownloadProgressChanged += handler;
try
{
using (token.Register(() => wcl.CancelAsync()))
{
await wcl.DownloadFileTaskAsync(new Uri(SRC), TARGET);
}
res = "Downloaded";
}
catch (Exception ex)
{
res = ex.Message + Environment.NewLine
+ ((ex.InnerException != null) ? ex.InnerException.Message : String.Empty);
}
wcl.Dispose();
return res;
}
}
}
使用系统；
Net系统；
使用系统线程；
使用System.Threading.Tasks；
使用System.Windows；
命名空间WebClientAsync
{
公共部分类主窗口：窗口
{
常量字符串SRC=”http://ovh.net/files/10Mio.dat";
常量字符串目标=@“d:\stuff\10Mio.dat”；
//恢复网络连接所需的时间
const int TIMEOUT=30*1000；
公共主窗口（）
{
初始化组件（）；
}
私有异步void btnDownload\u单击（对象发送方，路由目标）
{
btnDownload.IsEnabled=false；
btnDownload.Content=“下载”+SRC；
CancellationTokenSource cts=新的CancellationTokenSource（）；
CancellationToken=cts.token；
计时器=新计时器（（o）=>
{
//强制异步取消
cts.Cancel（）；
}
，null//state
，超时
，Timeout.Infinite//一次
);
DownloadProgressChangedEventHandler=（sa，ea）=>
{
//重新启动计时器
if（ea.bytesservedwcl.CancelAsync（））
{
等待wcl.DownloadFileTaskAsync（新Uri（SRC），目标）；
}
res=“下载”；
}
捕获（例外情况除外）
{
res=ex.Message+Environment.NewLine
+（（ex.InnerException！=null）？ex.InnerException.Message:String.Empty）；
}
wcl.Dispose（）；
返回res；
}
}
}
Task.DelayTask.WaitAny即可。例如：
static async Task DownloadFile(string url, string output, TimeSpan timeout) {
using (var wcl = new WebClient())
{
wcl.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
var download = wcl.DownloadFileTaskAsync(url, output);
// await two tasks - download and delay, whichever completes first
await Task.WhenAny(Task.Delay(timeout), download);
var exception = download.Exception; // need to observe exception, if any
bool cancelled = !download.IsCompleted && exception == null;
// download is not completed yet, nor it is failed - cancel
if (cancelled) {
wcl.CancelAsync();
}
if (cancelled || exception != null) {
// delete partially downloaded file if any (note - need to do with retry, might not work with a first try, because CancelAsync is not immediate)
int fails = 0;
while (true) {
try {
File.Delete(output);
break;
}
catch {
fails++;
if (fails >= 10)
break;
await Task.Delay(1000);
}
}
}
if (exception != null) {
throw new Exception("Failed to download file", exception);
}
if (cancelled) {
throw new Exception($"Failed to download file (timeout reached: {timeout})");
}
}
}
static async Task DownloadFile(string url, string output, TimeSpan timeout)
{
using (var wcl = new WebClient())
{
wcl.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
DateTime? lastReceived = null;
wcl.DownloadProgressChanged += (o, e) =>
{
lastReceived = DateTime.Now;
};
var download = wcl.DownloadFileTaskAsync(url, output);
// await two tasks - download and delay, whichever completes first
// do that until download fails, completes, or timeout expires
while (lastReceived == null || DateTime.Now - lastReceived < timeout) {
await Task.WhenAny(Task.Delay(1000), download); // you can replace 1 second with more reasonable value
if (download.IsCompleted || download.IsCanceled || download.Exception != null)
break;
}
var exception = download.Exception; // need to observe exception, if any
bool cancelled = !download.IsCompleted && exception == null;
// download is not completed yet, nor it is failed - cancel
if (cancelled)
{
wcl.CancelAsync();
}
if (cancelled || exception != null)
{
// delete partially downloaded file if any (note - need to do with retry, might not work with a first try, because CancelAsync is not immediate)
int fails = 0;
while (true)
{
try
{
File.Delete(output);
break;
}
catch
{
fails++;
if (fails >= 10)
break;
await Task.Delay(1000);
}
}
}
if (exception != null)
{
throw new Exception("Failed to download file", exception);
}
if (cancelled)
{
throw new Exception($"Failed to download file (timeout reached: {timeout})");
}
}
}
用法：
const string SRC = "http://ovh.net/files/10Mio.dat";
const string TARGET = @"d:\stuff\10Mio.dat";
// Time needed to restore network connection
TimeSpam TIMEOUT = TimeSpan.FromSeconds(30);
DownloadFile(SRC,TARGET, TIMEOUT); // might want to await this to handle exceptions
更新以回应评论。如果您希望超时基于接收到的数据，而不是整个操作时间，也可以使用Task.Delay
。例如：
static async Task DownloadFile(string url, string output, TimeSpan timeout) {
using (var wcl = new WebClient())
{
wcl.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
var download = wcl.DownloadFileTaskAsync(url, output);
// await two tasks - download and delay, whichever completes first
await Task.WhenAny(Task.Delay(timeout), download);
var exception = download.Exception; // need to observe exception, if any
bool cancelled = !download.IsCompleted && exception == null;
// download is not completed yet, nor it is failed - cancel
if (cancelled) {
wcl.CancelAsync();
}
if (cancelled || exception != null) {
// delete partially downloaded file if any (note - need to do with retry, might not work with a first try, because CancelAsync is not immediate)
int fails = 0;
while (true) {
try {
File.Delete(output);
break;
}
catch {
fails++;
if (fails >= 10)
break;
await Task.Delay(1000);
}
}
}
if (exception != null) {
throw new Exception("Failed to download file", exception);
}
if (cancelled) {
throw new Exception($"Failed to download file (timeout reached: {timeout})");
}
}
}
static async Task DownloadFile(string url, string output, TimeSpan timeout)
{
using (var wcl = new WebClient())
{
wcl.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
DateTime? lastReceived = null;
wcl.DownloadProgressChanged += (o, e) =>
{
lastReceived = DateTime.Now;
};
var download = wcl.DownloadFileTaskAsync(url, output);
// await two tasks - download and delay, whichever completes first
// do that until download fails, completes, or timeout expires
while (lastReceived == null || DateTime.Now - lastReceived < timeout) {
await Task.WhenAny(Task.Delay(1000), download); // you can replace 1 second with more reasonable value
if (download.IsCompleted || download.IsCanceled || download.Exception != null)
break;
}
var exception = download.Exception; // need to observe exception, if any
bool cancelled = !download.IsCompleted && exception == null;
// download is not completed yet, nor it is failed - cancel
if (cancelled)
{
wcl.CancelAsync();
}
if (cancelled || exception != null)
{
// delete partially downloaded file if any (note - need to do with retry, might not work with a first try, because CancelAsync is not immediate)
int fails = 0;
while (true)
{
try
{
File.Delete(output);
break;
}
catch
{
fails++;
if (fails >= 10)
break;
await Task.Delay(1000);
}
}
}
if (exception != null)
{
throw new Exception("Failed to download file", exception);
}
if (cancelled)
{
throw new Exception($"Failed to download file (timeout reached: {timeout})");
}
}
}
静态异步任务下载文件（字符串url、字符串输出、时间跨度超时）
{
使用（var wcl=new WebClient（））
{
wcl.Credentials=System.Net.CredentialCache.DefaultNetworkCredentials；
DateTime？lastReceived=null；
wcl.DownloadProgressChanged+=（o，e）=>
{
lastReceived=DateTime.Now；
};
var download=wcl.DownloadFileTaskAsync（url，输出）；
//等待两个任务-下载和延迟，以先完成者为准
//直到下载失败、完成或超时为止
while（lastReceived==null | | DateTime.Now-lastReceived=10）
打破
等待任务。延迟（1000）；
}
}
}
if（异常！=null）
{
抛出新异常（“下载文件失败”，异常）；
}
如果（取消）
{
抛出新异常（$“未能下载文件（达到超时：{timeout}）”；
}
}
}
就我个人而言，如果我要制作一个健壮的下载解决方案，我会添加一个网络连接监视器，因为这正是我们真正在等待的。为了简单起见，像这样的东西就足够了
online = true;
NetworkChange.NetworkAvailabilityChanged += NetworkChange_NetworkAvailabilityChanged;
_isNetworkOnline = NetworkInterface.GetIsNetworkAvailable();
void NetworkChange_NetworkAvailabilityChanged(object sender, NetworkAvailabilityEventArgs e)
{
online = e.IsAvailable;
}
然后，您可以实际检查网络可用性，并根据需要等待，然后再尝试下载或继续。。。我一定会接受这一点