转自：http://blog.163.com/xiaozhi797@126/blog/static/62440288201112245345838/
Webclient在下载请求时无法设置请求超时时间和请求读写超时时间。WebClient在异步下载时遇到网络不通等问题时没有响应超时造成app挂起。
1.Webclient请求超时设置
重写Webclient的GetWebRequest方法，为HttpWebRequest添加请求超时及读写超时
protected override WebRequest GetWebRequest(Uri address)
{
HttpWebRequest request = (HttpWebRequest)base.GetWebRequest(address); request.Timeout = 1000 * Timeout; request.ReadWriteTimeout = 1000 * Timeout; return request;
}
2.WebClient在异步下载
创建计时器监视响应情况，过期则取消下载
public class Calculagraph {
/// <summary> /// 时间到事件
/// </summary> public event TimeoutCaller TimeOver; /// <summary> /// 开始时间 /// </summary> private DateTime _startTime; private TimeSpan _timeout = new TimeSpan(0, 0, 10); private bool _hasStarted = false; object _userdata; /// <summary> /// 计时器构造方法 /// </summary> /// <param name="userdata">计时结束时回调的用户数据</param> public Calculagraph(object userdata) { TimeOver += new TimeoutCaller(OnTimeOver); _userdata = userdata; } /// <summary> /// 超时退出 /// </summary> /// <param name="userdata"></param> public virtual void OnTimeOver(object userdata) { Stop(); } /// <summary> /// 过期时间(秒) /// </summary> public int Timeout { get { return _timeout.Seconds; } set { if (value <= 0) return; _timeout = new TimeSpan(0, 0, value); } } /// <summary> /// 是否已经开始计时 /// </summary> public bool HasStarted { get { return _hasStarted; } } /// <summary> /// 开始计时 /// </summary> public void Start() { Reset(); _hasStarted = true; Thread th = new Thread(WaitCall); th.IsBackground = true; th.Start(); } /// <summary> /// 重置 /// </summary> public void Reset() { _startTime = DateTime.Now; } /// <summary> /// 停止计时 /// </summary> public void Stop() { _hasStarted = false; } /// <summary> /// 检查是否过期 /// </summary> /// <returns></returns> private bool checkTimeout() { return (DateTime.Now - _startTime).Seconds >= Timeout; } private void WaitCall() { try { //循环检测是否过期 while (_hasStarted && !checkTimeout()) { Thread.Sleep(1000); } if (TimeOver != null) TimeOver(_userdata); } catch (Exception) { Stop(); } } } /// <summary> /// 过期时回调委托 /// </summary> /// <param name="userdata"></param> public delegate void TimeoutCaller(object userdata);
public class CNNWebClient : WebClient { private Calculagraph _timer; private int _timeOut = 10; /// <summary> /// 过期时间 /// </summary> public int Timeout { get { return _timeOut; } set { if (value <= 0) _timeOut = 10; _timeOut = value; } } /// <summary> /// 重写GetWebRequest,添加WebRequest对象超时时间 /// </summary> /// <param name="address"></param> /// <returns></returns> protected override WebRequest GetWebRequest(Uri address) { HttpWebRequest request = (HttpWebRequest)base.GetWebRequest(address); request.Timeout = 1000 * Timeout; request.ReadWriteTimeout = 1000 * Timeout; return request; } /// <summary> /// 带过期计时的下载 /// </summary> public void DownloadFileAsyncWithTimeout(Uri address, string fileName, object userToken) { if (_timer == null) { _timer = new Calculagraph(this); _timer.Timeout = Timeout; _timer.TimeOver += new TimeoutCaller(_timer_TimeOver); this.DownloadProgressChanged += new DownloadProgressChangedEventHandler(CNNWebClient_DownloadProgressChanged); } DownloadFileAsync(address, fileName, userToken); _timer.Start(); } /// <summary> /// WebClient下载过程事件，接收到数据时引发 /// </summary> /// <param name="sender"></param> /// <param name="e"></param> void CNNWebClient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e) { _timer.Reset();//重置计时器 } /// <summary> /// 计时器过期 /// </summary> /// <param name="userdata"></param> void _timer_TimeOver(object userdata) { this.CancelAsync();//取消下载 } }WebClient的超时问题及解决,布布扣,bubuko.com
原文地址：http://www.cnblogs.com/elim/p/3848472.html
