我有一个新问题。我想对响应做一些操作,但我得到一个 NullReferenceException,因为它还没有到达......这是我的代码:
public partial class MainPage : PhoneApplicationPage
{
public static string res = null;
// Constructor
public MainPage()
{
InitializeComponent();
string Url = "http://twitter.com";
WebRequest req = WebRequest.Create(Url);
req.BeginGetResponse(new AsyncCallback(request_CallBack), req);
int i = MainPage.res.Length; // NullReferenceException
}
void request_CallBack(IAsyncResult result)
{
WebRequest webRequest = result.AsyncState as WebRequest;
WebResponse response = (WebResponse)webRequest.EndGetResponse(result);
Stream baseStream = response.GetResponseStream();
using (StreamReader reader = new StreamReader(baseStream))
{
res = reader.ReadToEnd();
Dispatcher.BeginInvoke(() => { MessageBox.Show("The response is arrived."); });
Dispatcher.BeginInvoke(() => { tbResponse.Text = res; });
}
}
}
但是当我使用 ManualResetEvent 类时,我的应用程序只是挂起,因为 if(dataReady.WaitOne()) 行。以下是 ManualResetEvent 类的完整代码:
public partial class MainPage : PhoneApplicationPage
{
public static string res = null;
ManualResetEvent dataReady;
// Constructor
public MainPage()
{
InitializeComponent();
string Url = "http://twitter.com";
dataReady = new ManualResetEvent(false);
WebRequest req = WebRequest.Create(Url);
req.BeginGetResponse(new AsyncCallback(request_CallBack), req);
if (dataReady.WaitOne())
{
int i = MainPage.res.Length;
}
}
void request_CallBack(IAsyncResult result)
{
WebRequest webRequest = result.AsyncState as WebRequest;
WebResponse response = (WebResponse)webRequest.EndGetResponse(result);
Stream baseStream = response.GetResponseStream();
using (StreamReader reader = new StreamReader(baseStream))
{
res = reader.ReadToEnd();
Dispatcher.BeginInvoke(() => { MessageBox.Show("The response is arrived."); });
Dispatcher.BeginInvoke(() => { tbResponse.Text = res; });
}
dataReady.Set();
}
}
所以,我的问题是:如何等待响应并对其进行操作? (我尝试使用 Application.DoEvent 方法,但它在 WP7 中不存在......)