BroadcastReceiver

BroadcastReceiver:廣播接收者，接收發送過來的廣播，本質是全局監聽器。廣播作爲Android一種通信方式，用途十分廣泛。例如：開機啓動後會接收到啓動服務的廣播，電量變化時會接收電量低及時保存的廣播提示，網絡變化會接收及時提示和保存的提示，檢測SD狀態廣播等等。
BroadcastReceiver的生命週期：
實現BroadcastReceiver的實例非常簡單，繼承BroadcastReceiver會調用onReceive()，所有的操作直接在onReceive()中運行。執行完之後，BroadcastReceiver直接銷燬。該方法直接運行在UI線程中，大概只有10s左右，所以不可做耗時操作。
如何註冊：
首先自定義一個BroadcastReceiver對象，繼承BroadcastReceiver

public class MyReceiver extends BroadcastReceiver {
    private static final String Tag = "Myreceive";
    @Override
    public void onReceive(Context context, Intent intent) {
        String msg = intent.getStringExtra("msg");
         Log.i(Tag,"Myreceive:"+ msg);
    }
}

註冊：
1.靜態註冊：在AndroidManifest.xml中實現

<receiver android:name=".MyReceiver">
    <intent-filter>
       <action android:name="MY_BROADCAST"/><!-- 隱式發送，用來匹配Intent-->
       <category android:name="android.intent.category.DEFAULT"/>
    </intent-filter>
</receiver>

補充（隱式跳轉）：
1.一個Intent可以有多個category目錄，但至少會有一個默認的；
2.只有Intent的所有category都匹配上了，Activity才能接受這個Intent。
所以爲什麼要加category 這個默認方式了。
MianActivity代碼：

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button bt_send = (Button) findViewById(R.id.bt_send);
        bt_send.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
           Intent intent = new  Intent("android.intent.action.MY_BROADCAST");//在配置文件中的action目錄做的配置
                                                intent.putExtra("msg","hello World");                                      sendBroadcast(intent);
                      }
               }
        );
    }

添加了一個發送按鈕，用來發送廣播
結果：

2.動態註冊

MyReceiver myReceiver = new MyReceiver();
IntentFilter intentFilter = new IntentFilter();      intentFilter.addAction("android.intent.action.MY_BROADCAST");
registerReceiver(myReceiver,intentFilter);//動態註冊

結果：

動態註冊在程序關閉時是收不到廣播的，但是靜態可以。

根據廣播的發送方式可以分爲：
1.Normal Broadcast普通廣播
2.System Broadcast系統廣播
3.Ordered Broadcast有序廣播
4.Local BroadcastApp內部廣播
5.Sticky Broadcast粘性廣播（5.0不在推薦）

1.普通廣播：
建立了三個自定義廣播類
MyReceiver

public class MyReceiver extends BroadcastReceiver {
    private static final String Tag = "Myreceive";

    @Override
    public void onReceive(Context context, Intent intent) {
        String msg = intent.getStringExtra("msg");
        Log.i(Tag, "Myreceive:" + msg);
    }
}

FirstReceiver

public class FirstReceiver extends BroadcastReceiver {
    private static final String Tag = "FirstReceiver";

    @Override
    public void onReceive(Context context, Intent intent) {
        String msg = intent.getStringExtra("msg");
        Log.i(Tag, "FirstReceiver:" + msg);
    }
}

SecondReceiver

public class SecondReceiver extends BroadcastReceiver {
    private static final String Tag = "SecondReceiver";

    @Override
    public void onReceive(Context context, Intent intent) {
        String msg = intent.getStringExtra("msg");
        Log.i(Tag, "SecondReceiver:" + msg);
    }
}

MainActivity：

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button bt_send = (Button) findViewById(R.id.bt_send);
        bt_send.setOnClickListener(new View.OnClickListener() {
       @Override
       public void onClick(View v) {
       Intent intent = new   Intent("android.intent.action.MY_BROADCAST");
       intent.putExtra("msg","hello World");
       sendBroadcast(intent);
                }
            }
        );
    }
}

在配置文件中添加相應的配置
結果：

04-06 08:01:34.308 30288-30288/com.appress.gerber.broadcastreceiver I/Myreceive: **Myreceive:hello World**
04-06 08:01:34.308 30288-30288/com.appress.gerber.broadcastreceiver I/FirstReceiver: **FirstReceiver:hello World**
04-06 08:01:34.308 30288-30288/com.appress.gerber.broadcastreceiver I/SecondReceiver: **SecondReceiver:hello World**

都接收到了消息。

有序廣播：
使用sendOrderedBroadcast()方法，優先級-1000到1000
在配置文件中配置優先級

    <receiver android:name=".MyReceiver">
        <intent-filter android:priority="10"><!--優先級10-->
            <action android:name="android.intent.action.MY_BROADCAST"/><!-- 隱式發送，用來匹配Intent-->
            <category android:name="android.intent.category.DEFAULT"/>
        </intent-filter>
    </receiver>
        <receiver android:name=".FirstReceiver">
            <intent-filter android:priority="80"><!--優先級80-->
                <action android:name="android.intent.action.MY_BROADCAST"/><!-- 隱式發送，用來匹配Intent-->
                <category android:name="android.intent.category.DEFAULT"/>
            </intent-filter>
        </receiver>
        <receiver android:name=".SecondReceiver">
            <intent-filter android:priority="-20"><!--優先級-20-->
                <action android:name="android.intent.action.MY_BROADCAST"/><!-- 隱式發送，用來匹配Intent-->
                <category android:name="android.intent.category.DEFAULT"/>
            </intent-filter>
        </receiver>

MainActivity：沒有做設置權限，直接null，如果設置權限只能接收相同權限的廣播。

 sendOrderedBroadcast(intent,null);

結果：優先級FirstReceiver，Myreceive，SecondReceiver

04-06 08:18:36.716 14590-14590/com.appress.gerber.broadcastreceiver I/FirstReceiver: **FirstReceiver:hello World**
04-06 08:18:36.716 14590-14590/com.appress.gerber.broadcastreceiver I/Myreceive: **Myreceive:hello World**
04-06 08:18:36.716 14590-14590/com.appress.gerber.broadcastreceiver I/SecondReceiver: **SecondReceiver:hello World**

Local Broadcast：App內部廣播，說明廣播可以跨進程之間通信。（自己不怎麼了解）
System Broadcast：Android系統內置了多個系統廣播，只要涉及到基本操作的基本上都帶有廣播