Question

我有以下用于连接REST的代码

    public void aquireToken() 
    {
         HttpWebRequest apiR = (HttpWebRequest)HttpWebRequest.Create(new Uri(apiUrl + "authorize?"));
        apiR.Method = "POST";

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

        apiR.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), apiR);
    }



    private void GetRequestStreamCallback(IAsyncResult callbackResult)
    {
        HttpWebRequest myRequest = (HttpWebRequest)callbackResult.AsyncState;
        // End the stream request operation
        Stream postStream = myRequest.EndGetRequestStream(callbackResult);

        // Create the post data
        string postData = "username=" + NTUser.username + "&appId=" + appId + "&signed=" + CreateSignedHex();


        byte[] byteArray = Encoding.UTF8.GetBytes(postData);

        // Add the post data to the web request
        postStream.Write(byteArray, 0, byteArray.Length);
        postStream.Close();

        // Start the web request
        myRequest.BeginGetResponse(new AsyncCallback(GetResponsetStreamCallback), myRequest);
    }

    private void GetResponsetStreamCallback(IAsyncResult callbackResult)
    {
        HttpWebRequest request = (HttpWebRequest)callbackResult.AsyncState;
        HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(callbackResult);
        using (StreamReader httpWebStreamReader = new StreamReader(response.GetResponseStream()))
        {
            string result = httpWebStreamReader.ReadToEnd();
            var u = JsonConvert.DeserializeObject<dynamic>(result);

            //string jsondata = u.data.toString();


            NTUser.token = JsonConvert.DeserializeObject<Token>(u.data.ToString());


        }
    }

问题是当从Phone UI调用aquireToken方法时，它不会等待httprequest完成，这导致nullreferences，因为下一个UI页面正试图访问不是的数据装了..

如何在从API获取所需信息的同时在UI线程上呈现一个简单的加载器？

提前致谢。

Answer 1

您必须等待代码完成。一种方法是将另一个参数传递给acquireToken，这将在操作完成时调用。

这样，调用acquireRoken方法的UI只知道在调用callbabl时才使用数据。

显示＆＃34;加载用户界面的一种方式＆＃34;在您的页面上放置一个“网格”元素，背景为黑色或白色半透明，其可见性设置为折叠。在该网格中放置一个进度条。在加载时，将所述网格的可见性更改为Visible，从而阻止UI并让您的海洋正在做某事。

public void DoUIThings()
{
     // Do some UI related things.
     acquireToken();
     // Don't continue doing things here.... Wait for the ContinueDoUIThings() to be called.
}

public void ContinueDoUIThings()
{
      // Now use your newly created token here...
      // Do some UI related things.
      // Note that this is called from below.
}

public void aquireToken() 
{
    // .... Your code was here..
    apiR.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), apiR);
}

private void GetRequestStreamCallback(IAsyncResult callbackResult)
{
    /// Your code was here.....
    myRequest.BeginGetResponse(new AsyncCallback(GetResponsetStreamCallback), myRequest);
}

private void GetResponsetStreamCallback(IAsyncResult callbackResult)
{
    HttpWebRequest request = (HttpWebRequest)callbackResult.AsyncState;
    HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(callbackResult);
    using (StreamReader httpWebStreamReader = new StreamReader(response.GetResponseStream()))
    {
        string result = httpWebStreamReader.ReadToEnd();
        var u = JsonConvert.DeserializeObject<dynamic>(result);

        //string jsondata = u.data.toString();
        NTUser.token = JsonConvert.DeserializeObject<Token>(u.data.ToString());

        // Added this call here...
        ContinueDoUIThings();

    }
}

Windows 8 Phone等待BeginGetRequestStream完成

1 个答案: