Question

I have an activity that displays a number. The number is obtained from SharedPreferences e.g

int num=pref.getInt(myAsyncTask.MYNUMBER,0);

The SharedPreference is loaded inside an AsyncTask where calculations take place (that involve retrieving data from db and so on). So, OnCreate() of the activity I run the Asynctask to calculate the value. However, the value is not always updated to the latest one when I launch the activity. This might be because Asynctask takes more time to calculate the new value than the the action of displaying the value inside the activity. How can I delay the execution of the method displaying the value until the Asynctask finishes with the process of the new one?

[[EDIT]]
I removed sharedpreferences. I use the onPostExecute() method to get the result. However, the behaviour is similar. The result is returned after the value is displayed so i couldn’t see anything at all.

Answer 1

If the calculation doesn’t take more than few second, the simplest solution is to use AsyncTask.get(), this method will block UI thread execution and make UI thread waiting for AsyncTask to finish:

public void onCreate(Bundle savedInstanceState) {
  ... ...
  MyAsyncTask myAsyncTask = nee MyAsyncTask();
  myAsyncTask.execute();
  myAsyncTask.get(); // alternatively you can use AsyncTask.(long timeout, TimeUnit unit)
  ... ...
}

Bear in mind that it blocks UI thrread execution, if your calculation is longer than 5 seconds, you will probably get ANR exception.

Since you already use AsyncTask, a more reasonable solution is moving execution of the method displaying the value into AsyncTask.onPostExecute(), this is the exactly reason why AsyncTask exist in API to solve this kind if scenario.