1.Android广播事件机制
Android的广播事件处理类似于普通的事件处理。不同之处在于，后者是靠点击按钮这样的组件行为来触发，而前者是通过构建Intent对象，使用sentBroadcast()方法来发起一个系统级别的事件广播来传递信息。广播事件的接收是通过定义一个继承Broadcast Receiver的类实现的，继承该类后覆盖其onReceive()方法,在该方法中响应事件。Android系统中定义了很多标准的Broadcast Action来响应系统广播事件。例如：ACTION_TIME_CHANGED（时间改变时触发）。但是，我们也可以自己定义Broadcast Receiver接收广播事件。
2.实现简单的定时提醒功能
主要包括三部分部分：?
1） 定时 - 通过定义Activity发出广播
2） 接收广播 - 通过实现BroadcastReceiver接收广播
3)?? 提醒 - 并通过Notification提醒用户
现在我们来具体实现这三部分：
2.1 如何定时，从而发出广播呢？
现在的手机都有闹钟的功能，我们可以利用系统提供的闹钟功能，来定时，即发出广播。具体地，在Android开发中可以用AlarmManager来实现。
AlarmManager 提供了一种系统级的提示服务，允许你安排在某个时间执行某一个服务。
AlarmManager的使用步骤说明如下：
1）获得AlarmManager实例： AlarmManager对象一般不直接实例化，而是通过Context.getSystemService(Context.ALARM_SERVIECE) 方法获得
2）定义一个PendingIntent来发出广播。
3）调用AlarmManager的相关方法，设置定时、重复提醒等功能。
详细代码如下：
package com.Reminder;
import java.util.Calendar;
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.Button;
/**
?* trigger the Broadcast event and set the alarm
?*/
public class ReminderSetting extends Activity {
????
??? Button btnEnable;
????
??? /** Called when the activity is first created. */
??? @Override
??? public void onCreate(Bundle savedInstanceState) {
??????? super.onCreate(savedInstanceState);
??????? setContentView(R.layout.main);
????????
??????? /* create a button. When you click the button, the alarm clock is enabled */
??????? btnEnable=(Button)findViewById(R.id.btnEnable);
??????? btnEnable.setOnClickListener(new View.OnClickListener() {
??????????? @Override
??????????? public void onClick(View v) {
??????????????? setReminder(true);
??????????? }
??????? });
??? }
????
??? /**
???? * Set the alarm?
???? *?
???? * @param b whether enable the Alarm clock or not?
???? */
??? private void setReminder(boolean b) {
????????
??????? // get the AlarmManager instance?
??????? AlarmManager am= (AlarmManager) getSystemService(ALARM_SERVICE);
??????? // create a PendingIntent that will perform a broadcast
??????? PendingIntent pi= PendingIntent.getBroadcast(ReminderSetting.this, 0, new Intent
(this,MyReceiver.class), 0);
????????
??????? if(b){
??????????? // just use current time as the Alarm time.?
??????????? Calendar c=Calendar.getInstance();
??????????? // schedule an alarm
??????????? am.set(AlarmManager.RTC_WAKEUP, c.getTimeInMillis(), pi);
??????? }
??????? else{
??????????? // cancel current alarm
??????????? am.cancel(pi);
??????? }
????????
??? }
}
2.2 接收广播
新建一个class 继承BroadcastReceiver，并实现onReceive()方法。当BroadcastReceiver接收到广播后，就会去执行OnReceive()方法。所以，我们在OnReceive()方法中加上代码，当接收到广播后就跳到显示提醒信息的Activity。
具体代码如下：
package com.Reminder;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
/**
?* Receive the broadcast and start the activity that will show the alarm
?*/
public class MyReceiver extends BroadcastReceiver {
??? /**
???? * called when the BroadcastReceiver is receiving an Intent broadcast.
???? */
??? @Override
??? public void onReceive(Context context, Intent intent) {
????????
??????? /* start another activity - MyAlarm to display the alarm */
??????? intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
??????? intent.setClass(context, MyAlarm.class);
??????? context.startActivity(intent);
????????
??? }
}
注意：创建完BroadcastReceiver后，需要在AndroidManifest.xml中注册：
<receiver android:name=".MyReceiver">?????
?????? <intent-filter>?
??????? <action android:name= "com.Reminder.MyReceiver" />?
??? </intent-filter>?
?</receiver>
2.3 提醒功能
新建一个Activity，我们在这个Activity中通过Android的Notification对象来提醒用户。我们将添加提示音,一个TextView来显示提示内容和并一个button来取消提醒。
其中，创建Notification主要包括：?
1）获得系统级得服务NotificationManager，通过 Context.getSystemService(NOTIFICATION_SERVICE)获得。
2）实例化Notification对象，并设置各种我们需要的属性，比如:设置声音。
3）调用NotificationManager的notify()方法显示Notification
详细代码如下：
package com.Reminder;
import android.app.Activity;
import android.app.Notification;
import android.app.NotificationManager;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore.Audio;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
/**
?* Display the alarm information?
?*/
public class MyAlarm extends Activity {
??? /**
???? * An identifier for this notification unique within your application
???? */
??? public static final int NOTIFICATION_ID=1;?
????
??? @Override
??? protected void onCreate(Bundle savedInstanceState) {
???????? super.onCreate(savedInstanceState);
???????? setContentView(R.layout.my_alarm);
????????
??????? // create the instance of NotificationManager
??????? final NotificationManager nm=(NotificationManager) getSystemService
(NOTIFICATION_SERVICE);
??????? // create the instance of Notification
??????? Notification n=new Notification();
??????? /* set the sound of the alarm. There are two way of setting the sound */
????????? // n.sound=Uri.parse("file:///sdcard/alarm.mp3");
??????? n.sound=Uri.withAppendedPath(Audio.Media.INTERNAL_CONTENT_URI, "20");
??????? // Post a notification to be shown in the status bar
??????? nm.notify(NOTIFICATION_ID, n);
???????
??????? /* display some information */
??????? TextView tv=(TextView)findViewById(R.id.tvNotification);
??????? tv.setText("Hello, it's time to bla bla...");
????????
??????? /* the button by which you can cancel the alarm */
??????? Button btnCancel=(Button)findViewById(R.id.btnCancel);
??????? btnCancel.setOnClickListener(new View.OnClickListener() {
????????????
??????????? @Override
??????????? public void onClick(View arg0) {
??????????????? nm.cancel(NOTIFICATION_ID);
??????????????? finish();
??????????? }
??????? });
??? }
????
}