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Editorial Team
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Asked: 2026-06-02T00:26:49+00:00

There are 2 Classes and 1 Interface: Class 1 = LoginPage, Class 2 =

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There are 2 Classes and 1 Interface: Class 1 = LoginPage, Class 2 = SyncData and Interface = AsyncTaskCompleteListener.

Class 1 uses Class 2 to sync information with the server. After Class 2 posts the result information in the onPostExecute method, the Interface callback method will be used to send the result information to Class 1. When I try to use the callback method, I get to see the following error:

04-12 11:06:43.715: W/dalvikvm(24941): threadid=1: thread exiting with uncaught exception (group=0x4001e578)
04-12 11:06:43.720: E/AndroidRuntime(24941): FATAL EXCEPTION: main
04-12 11:06:43.720: E/AndroidRuntime(24941): java.lang.NullPointerException
04-12 11:06:43.720: E/AndroidRuntime(24941):    at com.on_d_mand.live_evenementen.SyncData.onPostExecute(SyncData.java:101)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at com.on_d_mand.live_evenementen.SyncData.onPostExecute(SyncData.java:1)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at android.os.AsyncTask.finish(AsyncTask.java:417)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at android.os.AsyncTask.access$300(AsyncTask.java:127)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at android.os.Looper.loop(Looper.java:130)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at android.app.ActivityThread.main(ActivityThread.java:3691)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at java.lang.reflect.Method.invokeNative(Native Method)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at java.lang.reflect.Method.invoke(Method.java:507)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:912)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:670)
04-12 11:06:43.720: E/AndroidRuntime(24941):    at dalvik.system.NativeStart.main(Native Method)

Class 1 onTaskComplete method sample:

public void onTaskComplete(String result) {
    //perform action after receiving the information
    Toast.makeText(this, result, Toast.LENGTH_LONG).show(); 
}

Class 2 onPostExecute method sample:

public void onPostExecute(String RESULT) {

    if(dialog.isShowing()){
        dialog.dismiss();
    }

    callback.onTaskComplete(RESULT);

}

Class 3:

package com.on_d_mand.live_evenementen;

public interface AsyncTaskCompleteListener<T> {
    public void onTaskComplete(T result);
}

Does anyone knows what I’m doing wrong here? I hope it’s not too complicated with the Classes and the Interface.

Edit

The solution for this problem was by initialising the callback object in the Class 2 contructor.

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1 Answer

  1. Editorial Team

    You need to pass a reference to an object that implements your listener to your ‘SyncData’ class when you create it. Presumably, at the moment in your LoginPage you have something that looks like this:

     new SyncData().execute();

    You need to change this to:

     new SyncData(this).execute();

    And add a constructor to SyncData:

     public SyncData(AsyncTaskCompleteListener<String> callback)
 {
      this.callback = callback;
 }

    If you already have a constructor for SyncData, you will instead need to add the argument and code to the existing constructor.

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