[Android应用开发] 05.广播和服务

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广播接收者

• 现实中：电台要发布消息，通过广播把消息广播出去，使用收音机，就可以收听广播，得知这条消息

• Android中：系统在运行过程中，会产生会多事件，那么某些事件产生时，比如：电量改变、收发短信、拨打电话、屏幕解锁、开机，系统会发送广播，只要应用程序接收到这条广播，就知道系统发生了相应的事件，从而执行相应的代码。使用广播接收者，就可以收听广播

创建广播接收者

1. 定义java类继承BroadcastReceiver

2. 在清单文件中定义receiver节点，定义name属性，指定广播接收者java类的全类名

3. 在intent-filter的节点中，指定action子节点，action的值必须跟要接受的广播中的action匹配，比如，如果要接受打电话广播，

那么action的值必须指定为

    <action android:name="android.intent.action.NEW_OUTGOING_CALL"/>

• 因为打电话广播中所包含的action，就是"android.intent.action.NEW_OUTGOING_CALL"，所以我们定义广播接收者时，

  action必须与其匹配，才能收到这条广播

• 即便广播接收者所在进程已经被关闭，当系统发出的广播中的action跟该广播接收者的action匹配时，系统会启动该广播接收者所在的进程，并把广播发给该广播接收者。

短信防火墙

• 系统发送短信广播时，是怎么把短信内容存入广播的，我们就只能怎么取出来

• 如果短信过长，那么发送时会拆分成多条短信发送，那么短信广播中就会包含多条短信

• 4.0之后，广播接收者所在进程如果从来没启动过，那么广播接收者不会生效

• 4.0之后，如果系统自动关闭广播接收者所在进程，在广播中的action跟该广播接收者的action匹配时，系统会启动该广播接收者所在的进程，但是如果是用户手动关闭该进程，那么该进程会进入冻结状态，再也不会启动了，直到用户下一次手动启动该进程。

广播的分类

无序广播

• 所有与广播中的action匹配的广播接收者都可以收到这条广播，并且是没有先后顺序，视为同时收到

有序广播

• 所有与广播中的action匹配的广播接收者都可以收到这条广播，但是是有先后顺序的，按照广播接收者的优先级排序

服务

• Service

• 运行于后台的一个组件，用来运行适合运行在后台的代码，服务是没有前台界面，可以视为没有界面的activity

进程优先级

1. 前台进程：拥有一个正在与用户交互的Activity（onResume方法被调用）的进程

2. 可见进程：拥有一个可见但是没有焦点的Activity（onPause方法被调用）

3. 服务进程：拥有一个通过startService方法启动的服务

4. 后台进程：拥有一个不可见的Activity（onStop方法被调用）的进程

5. 空进程：没有拥有任何活动的应用组件的进程

电话录音机

电话的状态

打电话检测电话状态，用到的就是广播机制。

• 空闲状态（电话挂断）

    TelephonyManager.CALL_STATE_IDLE
  

• 响铃状态

    TelephonyManager.CALL_STATE_RINGING
  

• 摘机状态（通话中）

    TelephonyManager.CALL_STATE_OFFHOOK
  

录音机

录音，就是用到service。

• 音频文件的编码和格式不是一一对应的

本站文章为宝宝巴士 SD.Team原创，转载务必在明显处注明：（作者官方网站：宝宝巴士) 
转载自【宝宝巴士SuperDo团队】 原文链接: http://www.cnblogs.com/superdo/p/4912483.html