Service

Service

什麼是Service

• service是一個可以在後臺執行、長時間運行而不提供用戶界面的應用組件，也可爲其他應用提供一些功能接口。服務可由其他應用組件啓動，而且即使用戶切換到其他應用，服務仍將在後臺繼續運行。所謂的後臺是相對前臺而言的，具體就是說不依賴於用戶界面。
  service不是進程，不是線程。但service運行於所在進程的主線程，它有獨立的生命週期。

Service有哪些應用場景

• 下載文件，播放音樂，購買車票 等等

startService方式啓動Service怎麼做（啓動和停止及生命週期）

  private static final String TAG = "servers";


    @Override
    public void onCreate() {
        super.onCreate();
        Log.e(TAG, "onCreate: .................." );
    }

    @Override
    public int onStartCommand(final Intent intent, int flags, int startId) {
                  new Thread(new Runnable() {
                      int content=0;
                       String name=intent.getStringExtra("name");
                      @Override
                      public void run() {
                          while (content<100){
                              try {
                                  Thread.sleep(1000);
                                  content++;
                                  Log.e(TAG, "run:........."+content+name );
                              } catch (InterruptedException e) {
                                  e.printStackTrace();
                              }
                          }

                      }
                  }).start();

        return super.onStartCommand(intent, flags, startId);
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Log.e(TAG, "onBind: ............." );
        return null;
    }

    @Override

  @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.servicestart:
                Intent intent=new Intent(this,servers.class);
                intent.putExtra("name","張三");
                startService(intent);
                break;
            case  R.id.servicestop:
                Intent intent1=new Intent(this,servers.class);
                stopService(intent1);
                break;
        }

    }

bindService方式啓動Service怎麼做（綁定和解綁及生命週期）

   int count;
   private MyBinder myBinder=new MyBinder();
   boolean stopFlag;

    private class MyBinder extends Binder{
             public  int getCount(){
                  return count;
             }
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        System.out.print("執行onBind方法");
        return null;
    }

    @Override
    public boolean onUnbind(Intent intent) {
         System.out.print("執行onUnbind方法");
        return super.onUnbind(intent);
    }

    @Override
    public void onCreate() {
            System.out.print("執行onCreate方法");
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        System.out.print("執行onStartCommand方法");
        return super.onStartCommand(intent, flags, startId);

    }

    @Override
    public void onRebind(Intent intent) {
        super.onRebind(intent);
        System.out.print("rebind");
    }

    @Override
    public void onDestroy() {
      super.onDestroy();
      stopFlag=true;
      System.out.print("執行onDestroy");
    }
       class MyThread extends Thread{
           @Override
           public void run() {
               super.run();
               while (!stopFlag){
                   try {
                       Thread.sleep(1000);
                       System.out.print(Thread.currentThread().getName()+"---"+Thread.currentThread().getId());
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
                   count++;
                   System.out.print(count);
               }
           }
       }

    Button Myservicestart,Myservicestop;
    Intent intent;
    ServiceConnection conn=new  ServiceConnection(){

        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
             System.out.print("onServiceConnected");
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {
          System.out.print("onService");
          //MyserviceTwo myserviceTwo=(Myservice.MyBinder)service.getService();
            //ms.printServiceName();
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_myservices);
        binID();
         Intent intent=new Intent(this,Myservice.class);

    }

    private void binID() {
        Myservicestart=findViewById(R.id.Myservicestart);
        Myservicestop=findViewById(R.id.Myservicestop);
        Myservicestart.setOnClickListener(this);
        Myservicestop.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case  R.id.Myservicestart:
                bindService(intent, conn, Service.BIND_AUTO_CREATE);
                break;
            case R.id.Myservicestop:
                unbindService(conn);
                break;
        }
    }

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

IntentService有什麼不同

• IntentService是繼承Service的，那麼它包含了Service的全部特性，當然也包含service的生命週期，那麼與service不同的是，IntentService在執行onCreate操作的時候，內部開了一個線程，去你執行你的耗時操作。

IntentService怎麼用，注意事項

• IntentService解析及使用規範
  IntentService
  1 創建類繼承Service

public abstract class IntentService extends Service {
    private volatile Looper mServiceLooper;
    private volatile ServiceHandler mServiceHandler;
    private String mName;
    private boolean mRedelivery;

    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }
    }

    public IntentService(String name) {
        super();
        mName = name;
    }

    public void setIntentRedelivery(boolean enabled) {
        mRedelivery = enabled;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

    @Override
    public void onStart(@Nullable Intent intent, int startId) {
        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);
    }

    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
    }

    @Override
    public void onDestroy() {
        mServiceLooper.quit();
    }

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

    @WorkerThread
    protected abstract void onHandleIntent(@Nullable Intent intent);
}

2 創建Service
- 在Service被創建的時候，使用HandlerThread（繼承於 Thread）創建一個多線程並運行起來，使用HandlerThread線程的Looper來創建一個Handler，使得此Handler處理的所有任務都運行在非主線程裏。

public void onCreate() {

 public void onCreate() {
        super.onCreate();
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

3 處理任務

 public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }
        -----------------------------------------
    @Override
    public void onStart(@Nullable Intent intent, int startId) {
        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);
    }

    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICK;
    }

    @WorkerThread
    protected abstract void onHandleIntent(@Nullable Intent intent);

4 銷燬Service
- 務執行完畢後會調用stopSelf，在沒有任何任務正在執行或即將執行的情況下Service會停止運行.

  public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }

5 注意事項
- Service停止運行時要注意使用mServiceLooper.quit()退出Looper。如果不提供綁定服務默認返回null。

   @Override
    public void onDestroy() {
        mServiceLooper.quit();
    }

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