How to use an AsyncTask to do calculations in the background of an Android Activity: guesses a number on a background thread while showing updates on the UI. Full code below.

// TODO: Change all [[ and ]] to less-than and greater-than (YouTube limitation)
package ca.demo.asynctaskdemo;

import java.util.Random;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.widget.TextView;

/**
* Demonstration of how to use an AsyncTask by cracking a "password".
*/
public class MainActivity extends Activity {
private static final long PASSWORD = 12345;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
setContentView(R.layout.activity_main);
}

public void onClick_StartTask(View v) {
final long PUBLISH_RATE = 1000;
final long RANGE = 1000000;

// Start background task
PasswordGuesserTask crackerTask = new PasswordGuesserTask();
crackerTask.execute(RANGE, PUBLISH_RATE);
}

public void displayProgress(String message) {
TextView textView = (TextView) findViewById(R.id.txtStatus);
textView.setText(message);
}
public void displayAnswer(long answer) {
String message = "I know the password: " + answer;

TextView textView = (TextView) findViewById(R.id.txtFinalAnswer);
textView.setText(message);
}


/*
* Background task to crack the password.
*/
// Generics:
// 1. Long: Type of reference(s) passed to doInBackground()
// 2. String: Type of reference passed to onProgressUpdate()
// 3. Long: Type of reference returned by doInBackground()
// Value passed to onPostExecute()
// TODO: Change all [[ and ]] to less-than and greater-than (YouTube limitation)
private class PasswordGuesserTask extends AsyncTask[[Long, String, Long]] {

// Executed on main UI thread
@Override
protected void onPreExecute() {
super.onPreExecute();
MainActivity.this.setProgressBarIndeterminateVisibility(true);
}

// Run on background thread.
@Override
protected Long doInBackground(Long... arguments) {
// Extract arguments
long range = arguments[0];
long publishRate = arguments[1];

long guess = 0;
long count = 0;
Random rand = new Random();
while (guess != PASSWORD) {
guess = Math.abs(rand.nextLong()) % range;
count ++;

if (count % publishRate == 0) {
publishProgress(
"Guess #: " + count,
"Last guess: " + guess);
}
}
return guess;
}

// Executed on main UI thread.
@Override
protected void onProgressUpdate(String... values) {
super.onProgressUpdate(values);

String message = "";
for (String str : values) {
message += str + ", ";
}
displayProgress(message);
}

// Executed on main UI thread
@Override
protected void onPostExecute(Long result) {
super.onPostExecute(result);
displayAnswer(result);
MainActivity.this.setProgressBarIndeterminateVisibility(false);
}
}
}

свернуть