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我的应用程序使用用户名和密码，并在点击超链接按钮时，这些值被发送到服务器，因此服务器返回类似于 PASS:ClientID 的内容。只有当 responseString 包含 PASS 时，我才希望导航到 SecondPage.xaml（来自 MainPage.xaml.cs）。这是我的代码：

namespace aquila1
{
    public partial class MainPage : PhoneApplicationPage
    {
        static string username;
        static string password;
        static string rs;

        static NavigationService ns = new NavigationService();

        // Constructor
        public MainPage()
        {
            InitializeComponent();


        }

        private static ManualResetEvent allDone = new ManualResetEvent(true);

       private void HyperlinkButton_Click_1(object sender, RoutedEventArgs e)
       {
           username = textbox1.Text;
           password = textbox2.Text;
           System.Diagnostics.Debug.WriteLine(username);
           System.Diagnostics.Debug.WriteLine(password);

           HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://60.243.245.181/fms_tracking/php/mobile_login.php?username=" + username + "&password=" + password);


           request.ContentType = "application/x-www-form-urlencoded";

           // Set the Method property to 'POST' to post data to the URI.
           request.Method = "POST";

           // start the asynchronous operation
           request.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), request);

           // Keep the main thread from continuing while the asynchronous 
           // operation completes. A real world application 
           // could do something useful such as updating its user interface. 
           allDone.WaitOne();



       }


        private static void GetRequestStreamCallback(IAsyncResult asynchronousResult)
        {

            HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

            // End the operation
            Stream postStream = request.EndGetRequestStream(asynchronousResult);

            // Console.WriteLine("Please enter the input data to be posted:");
            string postData = username + "+" + password;
            System.Diagnostics.Debug.WriteLine(postData);
            // Convert the string into a byte array. 
            byte[] byteArray = Encoding.UTF8.GetBytes(postData);

            // Write to the request stream.
            postStream.Write(byteArray, 0, postData.Length);
            postStream.Close();

            // Start the asynchronous operation to get the response
            request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
        }

        private static void GetResponseCallback(IAsyncResult asynchronousResult)
        {
            HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

            // End the operation
            HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
            Stream streamResponse = response.GetResponseStream();
            StreamReader streamRead = new StreamReader(streamResponse);
           string responseString = streamRead.ReadToEnd();
            rs = responseString; 
            System.Diagnostics.Debug.WriteLine(responseString);
            System.Diagnostics.Debug.WriteLine("@@@@@");
            System.Diagnostics.Debug.WriteLine(rs);

            // Close the stream object
            streamResponse.Close();
            streamRead.Close();

            // Release the HttpWebResponse
            response.Close();
            move2();


            allDone.Set();

        }


       private static void move2()
       {

           string[] rs1 = rs.Split(':');
           if ((rs1[0].Trim()).Equals("PASS"))
           {

               ns.Navigate(new Uri("/SecondPage.xaml", UriKind.Relative));
           }
           else
           {
               MessageBox.Show(rs);
           }
       }



    }
}

在运行代码时，我总是得到 NullReferenceException 。

请帮我找出错误并提出更正建议。

提前致谢

4

1 回答 1

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您很可能会收到错误，因为 NavigationService 找不到资源/SecondPage.xaml。SecondPage 是否位于项目的根目录？

这也可能是由于在加载目标资源之前尝试导航（例如，通过在页面的构造函数中导航）造成的，但这似乎不是您的问题。

此答案表明更改命名空间或程序集名称后可能会出现此问题。它指出清理项目，确保所有 bin 和 obj 文件夹为空，然后重新编译将修复它。但是，它的参考链接已经失效。

于 2013-04-17T13:56:39.263 回答