How to make an Asynchronous Method return a value

Question

I know how to make Async methods but say I have a method that does a lot of work then returns a boolean value   How do I return the boolean value on the callback   Clarification   public bool Foo        Thread Sleep 100000      Do work     return true      I want to be able to make this asynchronous

User · Answer

Use a BackgroundWorker  It will allow you to get callbacks on completion and allow you to track progress  You can set the Result value on the event arguments to the resulting value       public void UseBackgroundWorker                 var worker   new BackgroundWorker            worker DoWork    DoWork          worker RunWorkerCompleted    WorkDone          worker RunWorkerAsync  input               public void DoWork object sender  DoWorkEventArgs e                e Result   e Argument Equals  input            Thread Sleep 1000              public void WorkDone object sender  RunWorkerCompletedEventArgs e                var result    bool  e Result

User · Answer

From C  5 0  you can specify the method as   public async Task lt bool gt  doAsyncOperation            do work     return true     bool result   await doAsyncOperation

User · Answer

Perhaps you can try to BeginInvoke a delegate pointing to your method like so          delegate string SynchOperation string value        class Program               static void Main string   args                        BeginTheSynchronousOperation CallbackOperation   my value                Console ReadLine                       static void BeginTheSynchronousOperation AsyncCallback callback  string value                        SynchOperation op   new SynchOperation SynchronousOperation               op BeginInvoke value  callback  op                      static string SynchronousOperation string value                        Thread Sleep 10000               return value                     static void CallbackOperation IAsyncResult result                           get your delegate             var ar   result AsyncState as SynchOperation                 end invoke and get value             var returned   ar EndInvoke result                Console WriteLine returned                      Then use the value in the method you sent as AsyncCallback to continue

User · Answer

You should use the EndXXX of your async method to return the value  EndXXX should wait until there is a result using the IAsyncResult s WaitHandle and than return with the value

User · Answer

Probably the simplest way to do it is to create a delegate and then BeginInvoke  followed by a wait at some time in the future  and an EndInvoke   public bool Foo        Thread Sleep 100000      Do work     return true     public SomeMethod         var fooCaller   new Func lt bool gt  Foo          Call the method asynchronously     var asyncResult   fooCaller BeginInvoke null  null           Potentially do other work while the asynchronous method is executing          Finally  wait for result     asyncResult AsyncWaitHandle WaitOne        bool fooResult   fooCaller EndInvoke asyncResult        Console WriteLine  Foo returned  0    fooResult

User · Answer

There are a few ways of doing that    the simplest is to have the async method also do the follow-on operation  Another popular approach is to pass in a callback  i e   void RunFooAsync      Action lt bool gt  callback            do some stuff      bool result             if callback    null  callback result       Another approach would be to raise an event  with the result in the event-args data  when the async operation is complete   Also  if you are using the TPL  you can use ContinueWith   Task lt bool gt  outerTask        outerTask ContinueWith task   gt        bool result   task Result         do something with that

[c#] How to make an Asynchronous Method return a value?

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