HttpWebRequest中的ObjectDisposedException

Question

我在Compact framework中创建了一个web请求，如下所示

HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create("Url");

using (StreamWriter streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
     streamWriter.Write("body");

using (HttpWebResponse response = httpWebRequest.GetResponse() as HttpWebResponse)
using (StreamReader streamReader = new StreamReader(response.GetResponseStream()))
{
     string json = streamReader.ReadToEnd();
}

我得到了一个ObjectDisposedException。我将这个错误归咎于response.GetResponseStream()，但是这段代码出了什么问题呢？

堆栈跟踪是

System.ObjectDisposedException 
ObjectDisposedException-   at System.Threading.Timer.throwIfDisposed()
   at System.Threading.Timer.Change(UInt32 dueTime, UInt32 period)
   at System.Threading.Timer.Change(Int32 dueTime, Int32 period)
   at System.Net.HttpWebRequest.ConnectionClient.Read(Byte[] data, Int32 offset, Int32 length)
   at System.Net.HttpReadStream.NetworkRead(Byte[] data, Int32 offset, Int32 length)
   at System.Net.ContentLengthReadStream.doRead(Byte[] data, Int32 offset, Int32 length)
   at System.Net.HttpReadStream.ReadToDrain(Byte[] buffer, Int32 offset, Int32 length)
   at System.Net.HttpReadStream.doClose()
   at System.Net.ContentLengthReadStream.doClose()
   at System.Net.HttpReadStream.Finalize()

Answer 1

我怀疑这是由于您处置了StreamWriter，而后者反过来又处置了请求流。我不知道这会对请求本身造成什么影响，但我猜这就是问题所在。

您可以随时使用Reflector深入BCL来查看到底发生了什么，但尝试这样的测试可能会更快、更容易：

HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create("Url");
StreamWriter streamWriter;
try
{
    streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
    streamWriter.Write("body");

    using (HttpWebResponse response = httpWebRequest.GetResponse() as HttpWebResponse)
    using (StreamReader streamReader = new StreamReader(response.GetResponseStream()))
    {
        string json = streamReader.ReadToEnd();
    }
}
finally
{
    streamWriter.Dispose();
}