Question

我只是创建简单的JsonDataManager以便以JSON格式编写并解析它以便稍后使用它，但JObject.Parse不等到webclient获取JSON数据并直接使用＆＃34;它将会是由JSON填充＆＃34;串。我怎么能推它等到它完全得到JSON字符串？

public class JsonDataManager{

         String myData = "its going to be filled by json";


        public JsonDataManager(string Category)
        {
            String url = "<a href="http://www.kaanbarisbayrak.com/?json=get_category_posts&cat="+Category;<br">http://www.kaanbarisbayrak.com/?json=get_category_posts&cat="+Catego...</a> />
            WebClient wc = new WebClient();
            wc.Encoding = System.Text.Encoding.UTF8;
            wc.Headers["Accept"] = "application/json";
            wc.DownloadStringAsync(new Uri(url), UriKind.Relative);
            wc.DownloadStringCompleted += new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);

        }


        public String getWriting()
        {
            JObject obj = JObject.Parse(myData);
            JArray array = (JArray)obj["posts"];
            string writing = (string)array[0]["content"]; 
            return writing;
        }



        private void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
        {
            myData = e.Result;
        }


    }

Answer 1

您需要等到WebClient完成下载。一种方法是使用ManualResetEvent：

public class JsonDataManager
{
   String myData = "its going to be filled by json";
   ManualResetEvent mre = new ManualResetEvent(false);

   public JsonDataManager(string Category)
   {
       String url = "<a href="http://www.kaanbarisbayrak.com/?json=get_category_posts&cat="+Category;<br">http://www.kaanbarisbayrak.com/?json=get_category_posts&cat="+Catego...</a> />
       WebClient wc = new WebClient();
       wc.Encoding = System.Text.Encoding.UTF8;
       wc.Headers["Accept"] = "application/json";
       wc.DownloadStringAsync(new Uri(url), UriKind.Relative);
       wc.DownloadStringCompleted += new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);
   }

   public String getWriting()
   {
       mre.WaitOne();
       JObject obj = JObject.Parse(myData);
       JArray array = (JArray)obj["posts"];
       string writing = (string)array[0]["content"]; 
       return writing;
   }

   private void wc_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
   {
       myData = e.Result;
       mre.Set();
   }
}

了解有关重置事件的更多here。

Answer 2

public class JsonDataManager
{
    readonly String _url;

    public JsonDataManager(string category)
    {
        _url = @"http://www.kaanbarisbayrak.com/?json=get_category_posts&cat="+category;
    }

    public async Task<String> getWriting()
    {
        WebClient wc = new WebClient();
        wc.Encoding = System.Text.Encoding.UTF8;
        wc.Headers["Accept"] = "application/json";

        JObject obj = JObject.Parse(await wc.DownloadStringTaskAsnync(_url));
        JArray array = (JArray)obj["posts"];
        string writing = (string)array[0]["content"]; 
        return writing;
    }
}

使用它：

var jsonManager = new JsonDataManager("whatever");
var writing = await jsonManager.getWriting();

此代码未经过测试，但我希望您明白这一点。

Answer 3

如果您尝试发布数据并获得json结果，我建议您使用 StreamReader 来正确获取响应。请看下面的方法，它会将结果作为字符串返回，你可以将它解析为json。

    public string GetJsonResult(string url, string queryStringValues)
    {
    // Create web request
    HttpWebRequest httpWebRequest;
    httpWebRequest = (HttpWebRequest)WebRequest.Create(url + queryStringValues);
    httpWebRequest.Method = "POST";
    httpWebRequest.Timeout = 6000;
    httpWebRequest.ContentType = "application/json";

    System.Net.ServicePointManager.Expect100Continue = false;

    // Make the request and get the response
    HttpWebResponse response = null;
    response = (HttpWebResponse)httpWebRequest.GetResponse();
    string content = "";
    using (var stream = new StreamReader(response.GetResponseStream()))
    {
    content = stream.ReadToEnd();
    }
    return content;
    }

Answer 4

我想你想使用Task<string>。这意味着getWriting()是最终返回字符串但不会阻塞该线程的函数。要执行此操作，只需将下载调用包装在任务中即可。然后，您可以附加一个ContinueWith函数作为您的回调函数，该函数接收结果并将其打印到屏幕上。

class JsonDataManager
{
    String url = "http://www.kaanbarisbayrak.com/?json=get_category_posts&cat=";
    string data = "";
    HttpClient hc;

    public JsonDataManager(string Category)
    {
        hc = new HttpClient();
        url += Category;
    }

    public Task<string> getWriting()
    {
        return Task.Factory.StartNew<string>(() =>
        {
            data = hc.GetStringAsync(url).Result;

            // use the resulting string
            JObject obj = JObject.Parse(data);
            JArray array = (JArray)obj["posts"];
            string writing = (string)array[0]["content"];
            return writing;
        });
    }
}

    private void Form1_Load(object sender, EventArgs e)
    {
        JsonDataManager manager = new JsonDataManager("4");
        manager.getWriting().ContinueWith((task) =>
        {
            string writing = task.Result;
            MessageBox.Show(writing);
        });
    }

C＃JObject.Parse（）如何等到它完全得到json字符串

4 个答案: