定義

Service是Android四大組件之一逾苫，也是可執(zhí)行的程序铺纽，有自己的生命周期。創(chuàng)建哟忍、配置Service和創(chuàng)建狡门、配置Activity的過程相似。和Activity一樣锅很，都是從Context派生出來的其馏。

分類

按啟動方式分

采用start的方式開啟服務(wù)

1. 定義一個類繼承Service
2. 在Manifest.xml文件中配置該Service
3. 使用Context的startService(Intent)方法啟動該Service
4. 不再使用時，調(diào)用stopService(Intent)方法停止該服務(wù)

生命周期
onCreate()--->onStartCommand()（onStart()方法已過時） ---> onDestory()
說明
??如果服務(wù)已經(jīng)開啟爆安，不會重復(fù)的執(zhí)行onCreate()叛复，而是會調(diào)用onStart()和onStartCommand()。服務(wù)停止的時候調(diào)用onDestory()扔仓。服務(wù)只會被停止一次褐奥。
特點
一旦服務(wù)開啟跟調(diào)用者(開啟者)就沒有任何關(guān)系了。開啟者退出了翘簇，開啟者掛了撬码，服務(wù)還在后臺長期的運(yùn)行。開啟者不能調(diào)用服務(wù)里面的方法版保。

示例

public class LocalService extends Service {
    // Binder given to clients
    private final IBinder mBinder = new LocalBinder();
    // Random number generator
    private final Random mGenerator = new Random();

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }


    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

    public class LocalBinder extends Binder {
        public LocalService getService() {
            return LocalService.this;
        }
    }

    /**
     * method for clients
     */
    public int getRandomNumber() {
        return mGenerator.nextInt(100);
    }
}

// 調(diào)用
Intent intent = new Intent(this, LocalService.class);
startService(intent);
// 停止
stopService(intent)呜笑；

采用bind的方式開啟服務(wù)

步驟

1.定義一個類繼承Service
2.在Manifest.xml文件中配置該Service
3.使用Context的bindService(Intent, ServiceConnection, int)方法啟動該Service
4.不再使用時，調(diào)用unbindService(ServiceConnection)方法停止該服務(wù)

生命周期
onCreate() --->onBind()--->onunbind()--->onDestory()

注意
??綁定服務(wù)不會調(diào)用onstart()或者onstartcommand()方法

特點
??bind的方式開啟服務(wù)彻犁，綁定服務(wù)叫胁，調(diào)用者掛了，服務(wù)也會跟著掛掉汞幢。綁定者可以調(diào)用服務(wù)里面的方法驼鹅。

示例

public class LocalService extends Service {
    // Binder given to clients
    private final IBinder mBinder = new LocalBinder();
    // Random number generator
    private final Random mGenerator = new Random();

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }


    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

    /**
     * Class used for the client Binder.  Because we know this service always
     * runs in the same process as its clients, we don't need to deal with IPC.
     */
    public class LocalBinder extends Binder {
        public LocalService getService() {
            // Return this instance of LocalService so clients can call public methods
            return LocalService.this;
        }
    }

    /**
     * method for clients
     */
    public int getRandomNumber() {
        return mGenerator.nextInt(100);
    }
}

// 綁定
Intent intent = new Intent(this, LocalService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);

// 獲取服務(wù)
private LocalService mService;
private boolean mBound = false;
private ServiceConnection mConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
        LocalService.LocalBinder binder = (LocalService.LocalBinder) iBinder;
        mService = binder.getService();
        mBound = true;
    }

    @Override
    public void onServiceDisconnected(ComponentName componentName) {
        mBound = false;
    }
};
// 調(diào)用服務(wù)的方法
if (mBound) {
    int number = mService.getRandomNumber();
    // do somtheing
}

// 調(diào)用者關(guān)閉時解綁服務(wù)
if (mBound) {
    unbindService(mConnection);
    mBound = false;
}

可用作多線程的服務(wù)（IntentService）