AsyncTask

ExampleAsyncTask task = new ExampleAsyncTask(this); task.execute(10);

private static class ExampleAsyncTask extends AsyncTask<Integer, Integer, String> { private WeakReference<MainActivity> activityWeakReference ; ExampleAsyncTask(MainActivity activity) { activityWeakReference = new WeakReference<MainActivity>(activity); } // This method will be executed on UI thread // Therefore we can access the UI view (progressBar), directly // But since It is a Non-static Inner class, It holds reference to the MainActivity Class, (May Cause Memory Leaks e.g. When Device is Rotated) // So to Solve this problem, we can either make this as `static` class or make this as separate top level class // But when we make this class as static, we cannot access the UI view directly // And to Solve this issue, we can use Weak Reference in the ExampleAsyncTask class @Override protected void onPreExecute() { super.onPreExecute(); // progressBar.setVisibility(View.VISIBLE); // But we need strong reference to access the UI view // So we'll get strong reference for the particular function only MainActivity activity = activityWeakReference.get(); // activityWeakReference.get() might return null, if MainActivity is destroyed if (activity == null || activity.isFinishing()) return; activity.progressBar.setVisibility(View.VISIBLE); // To summerize, we cannot keep a strong reference in the scope of a class // otherwise it could cause memory leaks // (We get strong reference to the MainActivity by default when we create Non-static Inner class in it) } // This method will be executed on background thread // Return type of this method is the same as Result type mentioned in the <> @Override protected String doInBackground(Integer... integers) { for (int i = 0; i <integers[0]; i++) { int percentage = (i * 100) / integers[0]; // This method will call onProgressUpdate() publishProgress(percentage); // publishProgress() will be called every one second try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } return "Finished"; } // The return value is passed to the onPostExecute() // This method will be executed on UI thread @Override protected void onProgressUpdate(Integer... values) { super.onProgressUpdate(values); // progressBar.setProgress(values[0]); MainActivity activity = activityWeakReference.get(); if (activity == null || activity.isFinishing()) return; activity.progressBar.setProgress(values[0]); } // This method will be executed on UI thread @Override protected void onPostExecute(String s) { super.onPostExecute(s); // Toast.makeText(MainActivity.this, s, Toast.LENGTH_SHORT).show(); // progressBar.setProgress(0); // progressBar.setVisibility(View.INVISIBLE); MainActivity activity = activityWeakReference.get(); if (activity == null || activity.isFinishing()) return; Toast.makeText(activity, s, Toast.LENGTH_SHORT).show(); activity.progressBar.setProgress(0); activity.progressBar.setVisibility(View.INVISIBLE); } }