Question

Asynctask have 4 override methods onPreExecute(), doInBackground(), onProgressUpdate(), onPostExecute()
except onProgressUpdate all are working.
What should I do so that onProgressUpdate() should work.
Can anybody please briefly explain me what’s the use of onProgressUpdate(), what should write within this?

Answer 1

onProgressUpdate() is used to operate progress of asynchronous operations via this method. Note the param with datatype Integer. This corresponds to the second parameter in the class definition. This callback can be triggered from within the body of the doInBackground() method by calling publishProgress().

Example

import android.app.Activity;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class AsyncTaskExample extends Activity {

    protected TextView _percentField;

    protected Button _cancelButton;

    protected InitTask _initTask;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        _percentField = (TextView) findViewById(R.id.percent_field);
        _cancelButton = (Button) findViewById(R.id.cancel_button);
        _cancelButton.setOnClickListener(new CancelButtonListener());
        _initTask = new InitTask();
        _initTask.execute(this);
    }

    protected class CancelButtonListener implements View.OnClickListener {

        public void onClick(View v) {
            _initTask.cancel(true);
        }
    }

    /**
     * sub-class of AsyncTask
     */
    protected class InitTask extends AsyncTask<Context, Integer, String> {

        // -- run intensive processes here
        // -- notice that the datatype of the first param in the class definition matches the param passed to this
        // method
        // -- and that the datatype of the last param in the class definition matches the return type of this method
        @Override
        protected String doInBackground(Context... params) {
            // -- on every iteration
            // -- runs a while loop that causes the thread to sleep for 50 milliseconds
            // -- publishes the progress - calls the onProgressUpdate handler defined below
            // -- and increments the counter variable i by one
            int i = 0;
            while (i <= 50) {
                try {
                    Thread.sleep(50);
                    publishProgress(i);
                    i++;
                }
                catch (Exception e) {
                    Log.i("makemachine", e.getMessage());
                }
            }
            return "COMPLETE!";
        }

        // -- gets called just before thread begins
        @Override
        protected void onPreExecute() {
            Log.i("makemachine", "onPreExecute()");
            super.onPreExecute();
        }

        // -- called from the publish progress
        // -- notice that the datatype of the second param gets passed to this method
        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
            Log.i("makemachine", "onProgressUpdate(): " + String.valueOf(values[0]));
            _percentField.setText((values[0] * 2) + "%");
            _percentField.setTextSize(values[0]);
        }

        // -- called if the cancel button is pressed
        @Override
        protected void onCancelled() {
            super.onCancelled();
            Log.i("makemachine", "onCancelled()");
            _percentField.setText("Cancelled!");
            _percentField.setTextColor(0xFFFF0000);
        }

        // -- called as soon as doInBackground method completes
        // -- notice that the third param gets passed to this method
        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            Log.i("makemachine", "onPostExecute(): " + result);
            _percentField.setText(result);
            _percentField.setTextColor(0xFF69adea);
            _cancelButton.setVisibility(View.INVISIBLE);
        }
    }
}