MainActivity.java

package io.nervous.alarmtest;

import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Build;
import android.os.Bundle;
import android.os.SystemClock;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        ((SeekBar)findViewById(R.id.seekBar)).setOnSeekBarChangeListener(
                new SeekBar.OnSeekBarChangeListener() {
                    @Override
                    public void onProgressChanged(SeekBar seekBar, int i, boolean b) {
                        ((TextView) findViewById(R.id.label)).setText(String.valueOf(i));
                    }

                    @Override
                    public void onStartTrackingTouch(SeekBar seekBar) {

                    }

                    @Override
                    public void onStopTrackingTouch(SeekBar seekBar) {

                    }
                }
        );

        ((Button)findViewById(R.id.rtcWakeup)).setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        setAlarm(AlarmManager.RTC_WAKEUP);
                    }
                }
        );
    }

    void setAlarm(int type) {
        int minutes = ((SeekBar)findViewById(R.id.seekBar)).getProgress();
        long msecs;
        if(minutes == 0) {
            msecs = 30 * 1000;
        } else {
            msecs = minutes * 60 * 1000;
        }
        Toast.makeText(
                this, "Alarm set for " + minutes + " minutes from now", Toast.LENGTH_LONG).show();
        long target;
        if(type == AlarmManager.RTC_WAKEUP) {
            target = System.currentTimeMillis() + msecs;
        } else {
            target = SystemClock.elapsedRealtime();
        }
        Log.w(getClass().getName(), "Expect alarm to go off at " + target + " (" + msecs + ")");
        SharedPreferences prefs = getSharedPreferences(getPackageName(), Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = prefs.edit();
        editor.putLong("expected", target);
        editor.commit();

        AlarmManager am = (AlarmManager)getSystemService(ALARM_SERVICE);
        Intent intent = new Intent(this, AlarmWakefulReceiver.class);
        PendingIntent pending = PendingIntent.getBroadcast(
                this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
            am.setExact(type, target, pending);
        } else {
            am.set(type, target, pending);
        }
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}