Question

I am new to programming and I have struggled with this for days and cannot get it to work.

I have a loop to execute some tasks. It will display a picture in an ImageView for that particular task. So it goes something like this:

• setImageResource
• do some task
• wait for 1 second
• then start everything again until the commands end
• when all commands end, close that activity by calling finish()

I tried to use a handler with runnable and asynctask but I cannot get it to work. The UI is always updated later than the 1 second delay. As I call finish() after the commands ends, the photo seems not show up at all.

for(int i=0; i<actions.size(); i++) {
            switch((int)actions.get(i)[0]) {
            case 0:
                ivActionIcon.setImageResource(R.drawable.image);
                sleeping=true;
                DelayAsyncTask delay=new DelayAsyncTask();
                delay.execute();
                while(sleeping){};
                break;
            }
        }
        finish();
class DelayAsyncTask extends AsyncTask<String, Void, Bitmap> {
    @Override
    protected Bitmap doInBackground(String... params) {
        try {
            Thread.sleep(5000);
        } catch(Exception e){
            e.printStackTrace();
        }
        return null;
    }
    @Override 
    protected void onPostExecute(Bitmap bitmap) {
        sleeping=false;
    }

}

I am using a variable “sleeping” to let the main thread to wait for the delay.

Answer 1

Just from taking a guess this loop is somewhere in a UI thread. That means that you are blocking the UI thread until the async finishes. That is a NO-NO! Why not just update the image in the onPostExecute? Something like

class DelayAsyncTask extends AsyncTask<String, Void, Bitmap> {
    @Override
    protected Bitmap doInBackground(String... params) {
        try {
            Thread.sleep(5000);
        } catch(Exception e){
            e.printStackTrace();
        }
        return null;
    }
    @Override 
    protected void onPostExecute(Bitmap bitmap) {
        ivActionIcon.setImageResource(R.drawable.new_image);
    }

obviously remove this line of code as well (I don’t think I ever know a reason for doing something like that anyway).

while(sleeping){};