等待 AsyncTask 完成

Question

In the OnCreate method, I have invoked 3 AsyncTask which basically fills data for the 3 Spinners. What I need is that I should have the Login button disabled till all 3 tasks finish. How can I achieve that ?

            new SpinnerDataFetcher("GetFreeDrivers1",(Spinner)findViewById(R.id.Spinner_1)).execute();

            new SpinnerDataFetcher("GetFreeDrivers2",(Spinner)findViewById(R.id.Spinner_2)).execute();

            new SpinnerDataFetcher("GetFreeDrivers3",(Spinner)findViewById(R.id.Spinner_3)).execute();

Answer 1

For that you have to Disable Button before calling new Spinner1DateFetcher and call Second from Spinner1DateFetcher method onPostExecute and same as Third Spinner method and in Third Spinner onPostExecute set Button to Enable ..

For Disable Button use

Button.setEnabled(false); 

and For Enable Button use

   Button.setEnabled(true); 

Edit :

for the parameter check you have to add Constuctor and check the condition like below way.

private class MyAsyncTask extends AsyncTask<Void, Void, Void> {

    public MyAsyncTask(boolean showLoading) {
        super();
        // do stuff
    }

    // doInBackground() et al.
}

Answer 2

Initialize your AsyncTask instance with a reference to the Activity/Fragment that creates it. Then signal back in onPostExecute when its done

eg

 class Spinner1DataFetcher extends AsyncTask<...> {
       public Spinner1DataFetch(YourActivityOrFragment activity) {
            _activity = activity;
       }

       protected void onPostExecute(...) {
           _activity.spinner_1_is_done();
      }
 }

Answer 3

Just increment a number that corresponds on how many AsyncTask are done.

        int s = 0;

        @Override
        public void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            new SpinnerDataFetcher(){
               @Override
                protected void onPostExecute(....) {
                   super.onPostExecute(...);
                   s++;
                   check();
                }

            }.execute(); 

            new SpinnerDataFetcher(){
               @Override
                protected void onPostExecute(....) {
                   super.onPostExecute(...);
                   s++;
                   check();
                }

            }.execute(); 

            new SpinnerDataFetcher(){
               @Override
                protected void onPostExecute(....) {
                   super.onPostExecute(...);
                   s++;
                   check();
                }

            }.execute(); 

        }

        public void check(){
          if(s >=3){
             s= 0;
            // enable button here
          }
        }

Answer 4

There are multiple ways how you can achieve this.

The straightforward way to implement this is create a counter which will trigger UI update.

final InterfaceTrigger trigger = new InterfaceTrigger();

new AsyncTask<>() {
    @Override
    protected void onPostExecute(Object o) {
        super.onPostExecute(o);
        trigger.finishJob();
        if (trigger.isTimeToUpdateUi()) {
           // TODO update your UI
        }
    }
    };

public class InterfaceTrigger {
    private static final int THRESHOLD = 3;
    private int counter;

    public synchronized void finishJob() {
        counter++;
    }

    public synchronized boolean isTimeToUpdateUi() {
        return counter == THRESHOLD;
    }
}

Another way is to use CyclicBarier and ExcutorService mechanism.