为什么没有调用BeginGetResponse回调?
本文关键字:回调 BeginGetResponse 调用 为什么 | 更新日期: 2023-09-27 18:10:48
我的代码:
namespace RequestApi
{
public partial class MainPage : PhoneApplicationPage
{
private BackgroundWorker bw;
private string ans;
private JObject ansJson;
private static ManualResetEvent allDone = new ManualResetEvent(false);
// Constructor
public MainPage()
{
InitializeComponent();
}
private void button1_Click(object sender, RoutedEventArgs e)
{
string url = "http://192.168.0.43:8182/Account/SignIn";
CreateRequest(url);
userId.Text = ansJson.Value<int>("user_id").ToString();
}
private void CreateRequest(string url)
{
Debug.WriteLine("CreateRequest");
HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);
req.ContentType = "application/json";
req.Method = "POST";
req.BeginGetRequestStream(new AsyncCallback(RequestCallback), req);
allDone.WaitOne();
}
private void RequestCallback(IAsyncResult aresult)
{
Debug.WriteLine("RequestCallback");
HttpWebRequest req = (HttpWebRequest)aresult.AsyncState;
Stream postStream = req.EndGetRequestStream(aresult);
string obj = "{ 'username': 'test_2@aragast.com', 'password': 'a123456' }";
JObject json = JObject.Parse(obj);
string s = JsonConvert.SerializeObject(json);
byte[] postdata = System.Text.Encoding.Unicode.GetBytes(s);
postStream.Write(postdata, 0, postdata.Length);
postStream.Close();
req.BeginGetResponse(new AsyncCallback(ResponseCallback), req);
}
private void ResponseCallback(IAsyncResult aresult)
{
Debug.WriteLine("ResponseCallback");
HttpWebRequest req = (HttpWebRequest)aresult.AsyncState;
HttpWebResponse resp = (HttpWebResponse)req.EndGetResponse(aresult);
StreamReader reader = new StreamReader(resp.GetResponseStream());
string response = reader.ReadToEnd();
Debug.WriteLine(response);
JObject responseJson = JObject.Parse(response);
ansJson = responseJson;
Debug.WriteLine("answersJson from responseCallback {0}", ansJson);
reader.Close();
resp.Close();
allDone.Set();
}
}
}
当我调试应用程序时,它进入CreateRequest然后进入RequestCallback,但随后它停止并且永远不会进入ResponseCallback,而是尝试userId。文本来分配asnJson值,该值为空,因为它没有输入ResponseCallback。当我做错了,为什么它从来没有进入ResponseCallback?
您的ManualResetEvent
是用true
作为参数创建的,因此它已经被标记为开始。这意味着allDone.Wait()
呼叫将立即继续…因此CreateRequest
将完成,并且您将立即尝试使用asnJson
变量,如您所说的是null
。我怀疑这将终止应用程序,因此您永远没有机会获得响应。
ManualResetEvent
的构造函数——你不应该在UI线程中等待这样的时间!你会阻止它,你就失去了Windows Phone 7让一切从一开始就异步化的全部意义。
相反,你的回调函数应该在完成后使用分派器回调UI线程。注意,您还应该有健壮的错误处理,以防请求出现任何错误。
与回答问题不完全相关,但答案块似乎是适合我即将提出的建议的唯一地方…通过使用using
块,您应该在流周围设置适当的资源保护,如下所示:
Stream postStream = req.EndGetRequestStream(aresult);
string obj = "{ 'username': 'test_2@aragast.com', 'password': 'a123456' }";
JObject json = JObject.Parse(obj);
string s = JsonConvert.SerializeObject(json);
byte[] postdata = System.Text.Encoding.Unicode.GetBytes(s);
postStream.Write(postdata, 0, postdata.Length);
postStream.Close();
新代码()也确保你的编码是正确的请求:你的web服务真的期待UTF-16吗?更常见的是web服务器使用UTF-8 (Encoding.UTF8)):
using (Stream postStream = req.EndGetRequestStream(aresult))
{
string obj = "{ 'username': 'test_2@aragast.com', 'password': 'a123456' }";
JObject json = JObject.Parse(obj);
string s = JsonConvert.SerializeObject(json);
byte[] postdata = System.Text.Encoding.Unicode.GetBytes(s);
postStream.Write(postdata, 0, postdata.Length);
}
原始代码: HttpWebResponse resp = (HttpWebResponse)req.EndGetResponse(aresult);
StreamReader reader = new StreamReader(resp.GetResponseStream());
string response = reader.ReadToEnd();
Debug.WriteLine(response);
JObject responseJson = JObject.Parse(response);
ansJson = responseJson;
Debug.WriteLine("answersJson from responseCallback {0}", ansJson);
reader.Close();
resp.Close();
新代码: using (HttpWebResponse resp = (HttpWebResponse)req.EndGetResponse(aresult))
using (StreamReader reader = new StreamReader(resp.GetResponseStream()))
{
string response = reader.ReadToEnd();
Debug.WriteLine(response);
JObject responseJson = JObject.Parse(response);
ansJson = responseJson;
Debug.WriteLine("answersJson from responseCallback {0}", ansJson);
}
我还建议用try..catch
块包围req
和resp
操作,以允许某些东西处理异常条件-否则它将冒气泡到AppDomain的异常处理程序(也可以通过UnhandledException事件挂钩)。