AsyncTask

How AsyncTask Work in Android

The AsyncTask executes everything in doInBackground() inside of another thread, which does not have access to the GUI where your views are.

preExecute() and postExecute() offer you access to GUI before and after the heavy lifting occurs in this new thread, you can even pass the result of the long operation to postExecute() to then show any results of processing.

You will then see your TextView text updated after the doInBackground completes.

import android.app.Activity;

import android.os.AsyncTask;

import android.os.Bundle;

import android.provider.Settings.System;

import android.view.View;

import android.widget.Button;

import android.widget.TextView;

import android.view.View.OnClickListener;

public class AsyncTaskActivity extends Activity implements OnClickListener {

    Button btn;

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        btn = (Button) findViewById(R.id.button1);

        // because we implement OnClickListener we only have to pass "this"

        // (much easier)

        btn.setOnClickListener(this);

    }

    public void onClick(View view) {

        // detect the view that was "clicked"

        switch (view.getId()) {

        case R.id.button1:

            new LongOperation().execute("");

            break;

        }

    }

    private class LongOperation extends AsyncTask<String, Void, String> {

        @Override

        protected String doInBackground(String... params) {

            for (int i = 0; i < 5; i++) {

                try {

                    Thread.sleep(1000);

                } catch (InterruptedException e) {

                    Thread.interrupted();

                }

            }

            return "Executed";

        }

        @Override

        protected void onPostExecute(String result) {

            TextView txt = (TextView) findViewById(R.id.output);

            txt.setText("Executed"); // txt.setText(result);

            // might want to change "executed" for the returned string passed

            // into onPostExecute() but that is upto you

        }

        @Override

        protected void onPreExecute() {}

        @Override

        protected void onProgressUpdate(Void... values) {}

    }

}