如何等待直到异步任务中另一个类的方法在Android中完成

Question

I am newbie in AsyncTask, and I got problem. I have AsyncTask, which saves info in DB by calling function from another class. The problem is that onPostExecute method is calling before my function finishes; Here is my code:

class checkNewReviews2 extends AsyncTask<List<ReviewList.ReviewItem>, Void, Void>{


    @Override
    protected Void doInBackground(List<ReviewList.ReviewItem>... reviewList) {

        int size = reviewList[0].size();
        if(size>0) {

            for (int i = 0; i < size; i++) {
                ReviewList.ReviewItem r = reviewList[0].get(i);
                ContentValues c = new ContentValues();
                c.put(LentaClass.LentaListEntry.FILM_ID, r.getFilm_id());
                c.put(LentaClass.LentaListEntry.USER_ID, r.getUser_id());
                c.put(LentaClass.LentaListEntry.REVIEW_TEXT, r.getReview_text());
                c.put(LentaClass.LentaListEntry.CREATED_AT, r.getCreated_at());
                c.put(LentaClass.LentaListEntry.REVIEW_TYPE, r.getReview_type());
                c.put(LentaClass.LentaListEntry.VIEWS, r.getViews());
                sqLiteDatabase.insert(LentaClass.LentaListEntry.TABLE_NAME, null, c);

                c.clear();
            }
            FilmHandler filmHandler = new FilmHandler(getContext());
            filmHandler.HandleFilms(reviewList[0]);
            UserHandler userHandler = new UserHandler(getContext());
            userHandler.HandleUsers(reviewList[0]);


        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);

        initiateRecyclerView();
    }
}

I already tried to put all calls into onPreExecute, but the result is still the same. Also as a notice, the first block of sql code (cycle) is succesfully handled, not as Film and User handlers. How should I call initiateRecyclerView after AsyncTask completely executed?

Answer 1

Your doInBackgound() method needs to "wait" for your FilmHandler , UserHandler classes to finish.

My guess is that your classes are working on a background thread so when you use them your code immediately continues to the return null statement - and finishing the background work, causing onPostExecute() to be called.

Change your classes implementation to work on the calling thread and not create their own.

Answer 2

您是否也可以在doinbackground参数中添加上下文。可能是getcontext返回null / Application Context

Answer 3

onPostExecute will execute only after completion of doInBackground. If the FilmHandler and Userhandler are implemented on separate thread , it can cause the issue. So to avoid this,do not use another thread to save data in DB (or) Performing some other sort of operatio instead complete the entire saving data in the doInBackground itself.

Else there is an another way which also you can archive the functionality. You need to add a call back for the filmHandler or userHandler functions and check for the update in doinBackground and based on it you can pass the result to PostExcecute()

class checkNewReviews2 extends AsyncTask<List<ReviewList.ReviewItem>, Void, Boolean>{


@Override
protected Void doInBackground(List<ReviewList.ReviewItem>... reviewList) {

    int size = reviewList[0].size();
    if(size>0) {

        for (int i = 0; i < size; i++) {
            ReviewList.ReviewItem r = reviewList[0].get(i);
            ContentValues c = new ContentValues();
            c.put(LentaClass.LentaListEntry.FILM_ID, r.getFilm_id());
            c.put(LentaClass.LentaListEntry.USER_ID, r.getUser_id());
            c.put(LentaClass.LentaListEntry.REVIEW_TEXT, r.getReview_text());
            c.put(LentaClass.LentaListEntry.CREATED_AT, r.getCreated_at());
            c.put(LentaClass.LentaListEntry.REVIEW_TYPE, r.getReview_type());
            c.put(LentaClass.LentaListEntry.VIEWS, r.getViews());
            sqLiteDatabase.insert(LentaClass.LentaListEntry.TABLE_NAME, null, c);

            c.clear();
        }


        FilmHandler filmHandler = new FilmHandler(YourActivity.this);
       boolean filmHandlerState =   filmHandler.HandleFilms(reviewList[0]);
        UserHandler userHandler = new UserHandler(YourActivity.this);
      boolean userHandlerState =   userHandler.HandleUsers(reviewList[0]);



        if(filmHandlerState && userHandlerState )
        {
        return true;
        } 
       else
       {
       return false;
       }
    }
}

@Override
protected void onPostExecute(Void result) {
    super.onPostExecute(result);

      if(result)
     {
       initiateRecyclerView();
     }
     else
     {
      // any one of the filmHandler or userHandler function has failed. so do your handling here 

}

}

In another point as stated by @user3413619 might be getContext() is returning null so, try to make it YourActivity.this

Answer 4

make doInBackground method return type boolean and pass result to postExecute boolean then check if result true do what method you want to call.

Thanks