AlarmManagerMainActivity.java

package com.example.alarmmanager;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.os.SystemClock;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Toast;

public class MainActivity extends Activity {
	final static private long UM_SEGUNDO = 1000;
	final static private long VINTE_SEGUNDOS = UM_SEGUNDO * 20;
	PendingIntent pi;
	BroadcastReceiver br;
	AlarmManager am;

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

		setup();
		findViewById(R.id.the_button).setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				am.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
						SystemClock.elapsedRealtime() + VINTE_SEGUNDOS, pi);

			}
		});
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	private void setup() {
		br = new BroadcastReceiver() {
			@Override
			public void onReceive(Context c, Intent i) {
				Toast.makeText(c, "Tarefa Executada", Toast.LENGTH_LONG).show();
			}
		};
		registerReceiver(br, new IntentFilter("com.example.alarmmanager"));
		pi = PendingIntent.getBroadcast(this, 0, new Intent(
				"com.example.alarmmanager"), 0);
		am = (AlarmManager) (this.getSystemService(Context.ALARM_SERVICE));
	}

	@Override
	protected void onDestroy() {
		am.cancel(pi);
		unregisterReceiver(br);
		super.onDestroy();
	}
}