Android广播事件机制及应用(实现简单的定时提醒功能)

人走丿茶凉 2011-08-19

涉及的主要内容:1)AlarmManager和PendingIntent2)BroadReceiver3)NotificationandNotificationManager

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BroadcastReceiver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BroadcastAction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BroadcastReceiver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(ReminderSetting.java):

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(MyReceiver.java):

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:

<receiverandroid:name=".MyReceiver">

<intent-filter>

<actionandroid: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:MyAlarm.java

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();
            }
        });
    }
    
}

注:关于提示音设置(Notification.sound),可以参考:http://developer.android.com/guide/topics/ui/notifiers/notifications.html中的相关部分。

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