Android: how to wait AsyncTask to finish in MainThread?

Question

I know that the first you gonna this is... why the heck on the world you then use AsyncTask.

So here is my problem i am working on some Android app (API 7 for android 2.1 or higher) , and i am testing on emulator and everything was fine, so then i tested on HTC Sensation and it says NetworkOnMainThreadExeption!

I was downloading some pictures and then draw on the map.

So to solve this problem every (internet connection) in this case downloading the pictures i must put on AsyncTask to work.

So i need a method how to know when all pictures are done so i can start drawing..

I was trying so much and no result i have no idea. I got one solution with handler but if run on slower net i get nullpointer(because the pictures are not downloaded).

So please help me.

EDIT:

here is the idea:

Bitmap bubbleIcon ;
    onCreate(){
     ...
// i am making call for Async
new ImgDown().execute(url);
//and then i calling functions and classes to draw with that picture bubbleIcon !
DrawOnMap(bubbleIcon);
}




//THIS IS ASYNC AND FOR EX. SUPPOSE I NEED TO DOWNLOAD THE PIC FIRST
     class ImgDown extends AsyncTask<String, Void, Bitmap> {

        private String url;

        public ImgDown() {
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            url = params[0];
            try {
                return getBitmapFromURL(url);
            } catch (Exception err) {
            }

            return null;

        }

        @Override
        protected void onPostExecute(Bitmap result) {
            bubbleIcon = result;
            bubbleIcon = Bitmap
                    .createScaledBitmap(bubbleIcon, 70, 70, true);

        }

        public Bitmap getBitmapFromURL(String src) {
            try {
                Log.e("src", src);
                URL url = new URL(src);
                HttpURLConnection connection = (HttpURLConnection) url
                        .openConnection();
                connection.setDoInput(true);
                connection.connect();
                InputStream input = connection.getInputStream();
                // /tuka decode na slika vo pomalecuk kvalitet!
                BitmapFactory.Options options = new BitmapFactory.Options();
                options.inSampleSize = 3;
                Bitmap myBitmap = BitmapFactory
                        .decodeStream(new FlushedInputStream(input));
                Log.e("Bitmap", "returned");
                return myBitmap;
            } catch (IOException e) {
                e.printStackTrace();
                Log.e("getBitmapFromURL", e.getMessage());
                return null;
            }
        }

        class FlushedInputStream extends FilterInputStream {
            public FlushedInputStream(InputStream inputStream) {
                super(inputStream);
            }

            public long skip(long n) throws IOException {
                long totalBytesSkipped = 0L;
                while (totalBytesSkipped < n) {
                    long bytesSkipped = in.skip(n - totalBytesSkipped);
                    if (bytesSkipped == 0L) {
                        int byteValue = read();
                        if (byteValue < 0) {
                            break; // we reached EOF
                        } else {
                            bytesSkipped = 1; // we read one byte
                        }
                    }
                    totalBytesSkipped += bytesSkipped;
                }
                return totalBytesSkipped;
            }
        }
    }

i hope now is more clear.

Answer 1

You can write your own Delegate to delegate info about finishing the task, using OOP principles:

task_delegate.java

public interface TaskDelegate {
    void TaskCompletionResult(String result);
}

main_activity.java

public class MainActivity extends Activity implements TaskDelegate {

    //call this method when you need     
    private void startAsynctask() {
      myAsyncTask = new MyAsyncTask(this);
      myAsyncTask.execute();
     }

//your code

    @Override
    public void TaskCompletionResult(String result) {
        GetSomethingByResult(result);
    }
}

my_asynctask.java

public class MyAsyncTask extends AsyncTask<Void, Integer, String> {

    private TaskDelegate delegate;

    protected MyAsyncTask(TaskDelegate delegate) {
        this.delegate = delegate;
    }

    //your code 

    @Override
    protected void onPostExecute(String result) {

        delegate.TaskCompletionResult(result);
    }
}

Answer 2

class OpenWorkTask extends AsyncTask {

    @Override
    protected Boolean doInBackground(String... params) {
        // do something
        return true;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        // The results of the above method
        // Processing the results here
        myHandler.sendEmptyMessage(0);
    }

}

Handler myHandler = new Handler() {

    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
        case 0:
            // calling to this function from other pleaces
            // The notice call method of doing things
            break;
        default:
            break;
        }
    }
};