Create alarm set on a specified time, using AlarmManager and BroadcastReceiver.

In this exercise, set alarm using AlarmManager to trigger our BroadcastReceiver on a specified time. We will use "TimePickerDialog" to set the target time.

Modify main.xml to add a Button to start the TimePickerDialog to set the alarm time, add a TextView to display the set time.

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

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />
    <Button
        android:id="@+id/startSetDialog"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" 
        android:text="Set Target Time"/>
    <TextView
        android:id="@+id/alarmprompt"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />
</LinearLayout>

In the main activity, AndroidTimeActivity, the main code to start Alarm is in setAlarm(Calendar targetCal) method. Retrieve AlarmManager by through getSystemService(Context.ALARM_SERVICE). And set our alarm with alarm type(RTC_WAKEUP), trigger time, and pendingIntent. AlarmReceiver is the class of our BroadcastReceiver, it's onReceive() method will be called when alram trigger.

AndroidTimeActivity.java

package com.exercise.AndroidTime;

import java.util.Calendar;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.app.TimePickerDialog;
import android.app.TimePickerDialog.OnTimeSetListener;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.TimePicker;

public class AndroidTimeActivity extends Activity {
 
 TimePicker myTimePicker;
 Button buttonstartSetDialog;
 TextView textAlarmPrompt;
 
 TimePickerDialog timePickerDialog;
 
 final static int RQS_1 = 1;
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        textAlarmPrompt = (TextView)findViewById(R.id.alarmprompt);
        
        buttonstartSetDialog = (Button)findViewById(R.id.startSetDialog);
        buttonstartSetDialog.setOnClickListener(new OnClickListener(){

   @Override
   public void onClick(View v) {
    textAlarmPrompt.setText("");
    openTimePickerDialog(false);
    
   }});

    }

  
 private void openTimePickerDialog(boolean is24r){
  Calendar calendar = Calendar.getInstance();
  
  timePickerDialog = new TimePickerDialog(
    AndroidTimeActivity.this, 
    onTimeSetListener, 
    calendar.get(Calendar.HOUR_OF_DAY), 
    calendar.get(Calendar.MINUTE), 
    is24r);
  timePickerDialog.setTitle("Set Alarm Time");  
        
  timePickerDialog.show();

 }
    
    OnTimeSetListener onTimeSetListener
    = new OnTimeSetListener(){

  @Override
  public void onTimeSet(TimePicker view, int hourOfDay, int minute) {

   Calendar calNow = Calendar.getInstance();
   Calendar calSet = (Calendar) calNow.clone();

   calSet.set(Calendar.HOUR_OF_DAY, hourOfDay);
   calSet.set(Calendar.MINUTE, minute);
   calSet.set(Calendar.SECOND, 0);
   calSet.set(Calendar.MILLISECOND, 0);
   
   if(calSet.compareTo(calNow) <= 0){
    //Today Set time passed, count to tomorrow
    calSet.add(Calendar.DATE, 1);
   }
   
   setAlarm(calSet);
  }};

 private void setAlarm(Calendar targetCal){

  textAlarmPrompt.setText(
    "\n\n***\n"
    + "Alarm is set@ " + targetCal.getTime() + "\n"
    + "***\n");
  
  Intent intent = new Intent(getBaseContext(), AlarmReceiver.class);
  PendingIntent pendingIntent = PendingIntent.getBroadcast(getBaseContext(), RQS_1, intent, 0);
  AlarmManager alarmManager = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
  alarmManager.set(AlarmManager.RTC_WAKEUP, targetCal.getTimeInMillis(), pendingIntent);
  
 }
  
}

AlarmReceiver.java

package com.exercise.AndroidTime;

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

public class AlarmReceiver extends BroadcastReceiver {

 @Override
 public void onReceive(Context arg0, Intent arg1) {
  Toast.makeText(arg0, "Alarm received!", Toast.LENGTH_LONG).show();

 }

}

Modify AndroidManifest.xml to add receiver ".AlarmReceiver".

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

    <uses-sdk android:minSdkVersion="10" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".AndroidTimeActivity"
            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=".AlarmReceiver" android:process=":remote" />
    </application>

</manifest>

Download the files.

Next:
- Cancel alarm with a matching PendingIntent

Related:
- Set alarm on specified date/time with DatePicker/TimePicker