Exercise: System services and receiver

6.1. Target

In this chapter we will schedule a receiver via the Android alert manager system service. Once called, it uses the Android vibrator manager and a popup message (Toast) to notify the user.

6.2. Implement project

Create a new project called de.vogella.android.alarm with the activity called AlarmActivity .

Create the following layout.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <EditText
        android:id="@+id/time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:hint="Number of seconds"
        android:inputType="numberDecimal" >
    </EditText>

    <Button
        android:id="@+id/ok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="startAlert"
        android:text="Start Counter" >
    </Button>

</LinearLayout>

Create the following broadcast receiver class. This class will get the vibrator service.

package de.vogella.android.alarm;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Vibrator;
import android.widget.Toast;

public class MyBroadcastReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
                Toast.makeText(context, "Don't panik but your time is up!!!!.",
                                Toast.LENGTH_LONG).show();
                // Vibrate the mobile phone
                Vibrator vibrator = (Vibrator) context.getSystemService(Context.VIBRATOR_SERVICE);
                vibrator.vibrate(2000);
        }

}

Register this class as a broadcast receiver in AndroidManifest.xml and request authorization to vibrate the phone.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.vogella.android.alarm"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

    <uses-permission android:name="android.permission.VIBRATE" >
    </uses-permission>

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <activity
            android:name=".AlarmActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <receiver android:name="MyBroadcastReceiver" >
        </receiver>
    </application>

</manifest>

Change the code of your AlarmActivity class to the following. This activity creates an intent to start the receiver and register this intent with the alarm manager service.

package de.vogella.android.alarm;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class AlarmActivity extends Activity {
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
        }

        public void startAlert(View view) {
                EditText text = (EditText) findViewById(R.id.time);
                int i = Integer.parseInt(text.getText().toString());
                Intent intent = new Intent(this, MyBroadcastReceiver.class);
                PendingIntent pendingIntent = PendingIntent.getBroadcast(
                                this.getApplicationContext(), 234324243, intent, 0);
                AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
                alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis()
                                + (i * 1000), pendingIntent);
                Toast.makeText(this, "Alarm set in " + i + " seconds",
                                Toast.LENGTH_LONG).show();
        }

}

6.3. Validate implementation

Run your application on the device. Set your time and start the alarm. After the defined number of seconds a Toast should be displayed. Keep in mind that the vibration alarm does not work on the Android emulator.