android asynctask sending callbacks to ui

Question

I have the following asynctask class which is not inside the activity  In the activity I m initializing the asynctask  and I want the asynctask to report callbacks back to my activity  Is it possible  Or does the asynctask must be in the same class file as the activity    protected void onProgressUpdate Integer    values         super onProgressUpdate values       caller sometextfield setText  bla        Something like this

User · Answer

I felt the below approach is very easy   I have declared an interface for callback  public interface AsyncResponse       void processFinish Object output       Then created asynchronous Task for responding all type of parallel requests   public class MyAsyncTask extends AsyncTask lt Object  Object  Object gt         public AsyncResponse delegate   null   Call back interface      public MyAsyncTask AsyncResponse asyncResponse            delegate   asyncResponse   Assigning call back interfacethrough constructor             Override     protected Object doInBackground Object    params           My Background tasks are written here        return  resutl Object               Override     protected void onPostExecute Object result            delegate processFinish result              Then Called the asynchronous task when clicking a button in activity Class   public class MainActivity extends Activity         Override     public void onCreate Bundle savedInstanceState             Button mbtnPress    Button  findViewById R id btnPress            mbtnPress setOnClickListener new View OnClickListener                   Override             public void onClick View v                     MyAsyncTask asyncTask  new MyAsyncTask new AsyncResponse                           Override                     public void processFinish Object output                            Log d  Response From Asynchronous task     String  output                                     mbtnPress setText  String  output                                                             asyncTask execute new Object      Youe request to aynchronous task class is giving here                                             Thanks

User · Answer

IN completion to above answers  you can also customize your fallbacks for each async call you do  so that each call to the generic ASYNC method will populate different data  depending on the onTaskDone stuff you put there     Main FragmentCallback FC  new  Main FragmentCallback                 Override             public void onTaskDone String results                     localText setText results     example TextView                           new API CALL this getApplicationContext     GET  FC  execute   amp Books     Main Books     amp args     profile id     Remind  I used interface on the main activity thats where  Main  comes   like this   public interface FragmentCallback       public void onTaskDone String results         My API post execute looks like this      Override     protected void onPostExecute String results             Log i  TASK Result   results           mFragmentCallback onTaskDone results            The API constructor looks like this    class  API CALL extends AsyncTask lt String Void String gt          private Main FragmentCallback mFragmentCallback      private Context act      private String method        public API CALL Context ctx  String api method Main FragmentCallback fragmentCallback            act ctx          method api method          mFragmentCallback   fragmentCallback

User · Answer

You can create an interface  pass it to AsyncTask  in constructor   and then call method in onPostExecute    For example   Your interface   public interface OnTaskCompleted      void onTaskCompleted        Your Activity   public class YourActivity implements OnTaskCompleted         your Activity     And your AsyncTask   public class YourTask extends AsyncTask lt Object Object Object gt     change Object to required type     private OnTaskCompleted listener       public YourTask OnTaskCompleted listener           this listener listener                required methods      protected void onPostExecute Object o              your stuff         listener onTaskCompleted              EDIT  Since this answer got quite popular  I want to add some things   If you re a new to Android development  AsyncTask is a fast way to make things work without blocking UI thread  It does solves some problems indeed  there is nothing wrong with how the class works itself  However  it brings some implications  such as    Possibility of memory leaks  If you keep reference to your Activity  it will stay in memory even after user left the screen  or rotated the device   AsyncTask is not delivering result to Activity if Activity was already destroyed  You have to add extra code to manage all this stuff or do you operations twice  Convoluted code which does everything in Activity   When you feel that you matured enough to move on with Android  take a look at this article which  I think  is a better way to go for developing your Android apps with asynchronous operations

User · Answer

I will repeat what the others said  but will just try to make it simpler     First  just create the Interface class  public interface PostTaskListener lt K gt           K is the type of the result object of the async task      void onPostTask K result       Second  create the AsyncTask  which can be an inner static class of your activity or fragment  that uses the Interface  by including a concrete class  In the example  the PostTaskListener is parameterized with String  which means it expects a String class as a result of the async task   public static class LoadData extends AsyncTask lt Void  Void  String gt         private PostTaskListener lt String gt  postTaskListener       protected LoadData PostTaskListener lt String gt  postTaskListener           this postTaskListener   postTaskListener              Override     protected void onPostExecute String result            super onPostExecute result            if  result    null  amp  amp  postTaskListener    null              postTaskListener onPostTask result             Finally  the part where your combine your logic  In your activity   fragment  create the PostTaskListener and pass it to the async task  Here is an example       PostTaskListener lt String gt  postTaskListener   new PostTaskListener lt String gt           Override     public void onPostTask String result              Your post execution task code             Create the async task and pass it the post task listener  new LoadData postTaskListener     Done

[android] android asynctask sending callbacks to ui

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