Calling async method on button click

Question

I created Windows Phone 8 1 project and I am trying to run async method GetResponse string url  on button click and waiting for the method to finish  but method is never finishing  Here is my code   private void Button Click object sender  RoutedEventArgs          Task lt List lt MyObject gt  gt  task   GetResponse lt MyObject gt   my url          task Wait          var items   task Result    break point here    public static async Task lt List lt T gt  gt  GetResponse lt T gt  string url        List lt T gt  items   null      HttpWebRequest request    HttpWebRequest HttpWebRequest Create url        var response    HttpWebResponse await Task Factory FromAsync lt WebResponse gt  request BeginGetResponse  request EndGetResponse  null       try               Stream stream   response GetResponseStream            StreamReader strReader   new StreamReader stream           string text   strReader ReadToEnd            items   JsonConvert DeserializeObject lt List lt T gt  gt  text             catch  WebException                throw            return items      It will hang on task Wait     I changed my button click method to async and used await before the async method and I get the result await GetResponse lt string gt   url     What is wrong with Task lt List lt string gt  gt  task   GetResponse lt string gt   url      What am I doing wrong   Thanks for the help

User · Answer

use below code   Task WaitAll Task Run async      gt  await GetResponse lt MyObject gt   my url

User · Answer

You re the victim of the classic deadlock  task Wait   or task Result is a blocking call in UI thread which causes the deadlock   Don t block in the UI thread  Never do it  Just await it   private async void Button Click object sender  RoutedEventArgs          var task   GetResponseAsync lt MyObject gt   my url          var items   await task      Btw  why are you catching the WebException and throwing it back  It would be better if you simply don t catch it  Both are same   Also I can see you re mixing the asynchronous code with synchronous code inside the GetResponse method  StreamReader ReadToEnd is a blocking call --you should be using StreamReader ReadToEndAsync   Also use  Async  suffix to methods which returns a Task or asynchronous to follow the TAP  Task based Asynchronous Pattern   convention as Jon says   Your method should look something like the following when you ve addressed all the above concerns   public static async Task lt List lt T gt  gt  GetResponseAsync lt T gt  string url        HttpWebRequest request    HttpWebRequest HttpWebRequest Create url       var response    HttpWebResponse await Task Factory FromAsync lt WebResponse gt  request BeginGetResponse  request EndGetResponse  null        Stream stream   response GetResponseStream        StreamReader strReader   new StreamReader stream       string text   await strReader ReadToEndAsync         return JsonConvert DeserializeObject lt List lt T gt  gt  text

User · Answer

This is what s killing you   task Wait      That s blocking the UI thread until the task has completed - but the task is an async method which is going to try to get back to the UI thread after it  pauses  and awaits an async result  It can t do that  because you re blocking the UI thread     There s nothing in your code which really looks like it needs to be on the UI thread anyway  but assuming you really do want it there  you should use   private async void Button Click object sender  RoutedEventArgs        Task lt List lt MyObject gt  gt  task   GetResponse lt MyObject gt   my url        var items   await task         Presumably use items here     Or just   private async void Button Click object sender  RoutedEventArgs        var items   await GetResponse lt MyObject gt   my url           Presumably use items here     Now instead of blocking until the task has completed  the Button Click method will return after scheduling a continuation to fire when the task has completed   That s how async await works  basically    Note that I would also rename GetResponse to GetResponseAsync for clarity

[c#] Calling async method on button click

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