Windows phone 7 我如何等待响应并对其进行操作？

我有一个新问题。我想对响应执行一些操作，但是我得到了一个NullReferenceException，因为它还没有到达。。。这是我的密码：

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();
    }
}

因此，我的问题是：如何等待响应并对其进行操作？

---

（我试图使用Application.DoEvent方法，但它在WP7中不存在…

您不能将该代码

int i = MainPage.res.Length; // NullReferenceException

在

request\u回调

函数上

像

---

当前，您使用的是

WebRequest

的异步方法之一。如果要等待响应，只需使用等效的同步方法

GetResponse

{ 公共静态字符串res=null

// Constructor
public MainPage()
{
    InitializeComponent();
    string Url = "http://twitter.com";
    WebRequest req = WebRequest.Create(Url);
    req.BeginGetResponse(new AsyncCallback(request_CallBack), req);

}

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; });
    }
    int i = MainPage.res.Length; //No  NullReferenceException
}

---

}

没错，但我的代码只是一个简化的示例。。。在

req.BeginGetResponse（新的异步回调（request\u回调），req）之后行有很多函数，它们将运行。。。所以我必须等待回应，只是我不知道如何…不，你不能
WebRequest.GetResponse
在手机的API子集中不存在。是的，这是真的，但我的代码只是一个简化的示例。。。在req.BeginGetResponse（新的异步回调（请求回调），req）之后；行有很多函数，它们将运行，它们需要响应。。。我不能把所有这些函数都放在回调函数中。
public partial class MainPage : PhoneApplicationPage

// Constructor
public MainPage()
{
    InitializeComponent();
    string Url = "http://twitter.com";
    WebRequest req = WebRequest.Create(Url);
    req.BeginGetResponse(new AsyncCallback(request_CallBack), req);

}

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; });
    }
    int i = MainPage.res.Length; //No  NullReferenceException
}