HttpWebRequest 异常处理
我正在创建一个异步 HttpWebRequest，如果失败，我想调用备份 Web 服务。像这样：
public void CallService1()
{
HttpWebRequest request = HttpWebRequest.Create("http://MyFirstWebService")
request.BeginGetResponse(this.CallService1Completed, request);
}
public void CallService1Completed(IAsyncResult result)
{
HttpWebRequest request = (HttpWebRequest)result.AsyncState;
try
{
using (HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result))
{
using (Stream responseStream = response.GetResponseStream())
{
// Use Data
}
}
}
catch (WebException webException)
{
if (?????)
{
CallBackupService2();
}
}
}
请记住，这是一个移动应用程序，您可能并不总是有互联网连接。如果没有互联网连接，我不想调用备份服务。我只想在第一个服务因某种原因关闭时调用备份服务。我会在上面的“IF”语句中添加什么。
I am making an asyncronous HttpWebRequest and if that fails, I want to call a backup web service. Like so:
public void CallService1()
{
HttpWebRequest request = HttpWebRequest.Create("http://MyFirstWebService")
request.BeginGetResponse(this.CallService1Completed, request);
}
public void CallService1Completed(IAsyncResult result)
{
HttpWebRequest request = (HttpWebRequest)result.AsyncState;
try
{
using (HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(result))
{
using (Stream responseStream = response.GetResponseStream())
{
// Use Data
}
}
}
catch (WebException webException)
{
if (?????)
{
CallBackupService2();
}
}
}
Bearing in mind that this is a mobile applications where you may not always have an internet connection. I do not want to call the backup service if there is no internet connection. I only want to call the backup service if the first service is down for some reason. What would I put in the 'IF' statement above.
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它可以这样实现：
It can be implemented like: