android - 为什么 Service 在 Activity 被销毁时会 self 销毁？

Question

我想从一个 Activity 启动一个服务，然后让它在 Activity 退出/完成时继续运行。然后，当我再次启动应用 Activity 时，它会重新附加到现有服务。

我已经阅读了有关 bindService 的文档，但每次我点击后退按钮退出 Activity 时，都会自动调用服务的 onUnBind，从而有效地终止服务。我想我必须在服务解除绑定(bind)之前手动调用 unbindService。

我确实知道，一旦 Activity 被销毁，成员变量 mService、mBound 和 tv 就必须在新 Activity 创建后重新填充，因此下面的简单代码将显示 “bindService 已启动”也就不足为奇了。 " 但我本以为 LocalService 实例中的所有成员变量都是相同的，没有变化，所以 "bindService 已经启动。Val = "+ mService.myval; 应该保持每次我重新启动一个新的 Activity 时都一样，不是吗？

主 Activity

public class MainActivity extends AppCompatActivity
{
    LocalService mService;
    Boolean mBound = false;
    TextView tv;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tv = (TextView)findViewById(R.id.textView);    
    }

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

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

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

    public void onButtonStart(View v)
    {
        String str;

        // Bind to LocalService
        if (!mBound)
        {
            Intent intent = new Intent(this, LocalService.class);

            if (!bindService(intent, mConnection, Context.BIND_AUTO_CREATE))
            {
                unbindService(mConnection);
                str = "bindService failed?!";
            }
            else
            {
                str = "bindService started.";
            }
        }
        else
            str = "bindService already Started. Val = " + mService.myval;

        tv.setText(str);
    }  

    public void onButtonStop(View v)
    {
        if (mBound)
        {
            mService.stop();
            unbindService(mConnection);
            mBound = false;

            tv.setText("Stopped Service");
        }
        else
            tv.setText("Service is not running");
    }

    private ServiceConnection mConnection = new ServiceConnection()
    {
        @Override
        public void onServiceConnected(ComponentName className, IBinder service)
        {
            // We've bound to LocalService, cast the IBinder and get LocalService instance
            LocalService.LocalBinder binder = (LocalService.LocalBinder) service;
            mService = binder.getService();
            mBound = true;
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0)
        {
            mBound = false;
        }
    };   
 }

本地服务

public class LocalService extends Service
{
    private final IBinder mBinder = new LocalBinder();
    private final Random mGenerator = new Random();
    public int myval = getRandomNumber();

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

    // Service is being Destroyed
    @Override
    public void onDestroy()
    {
        super.onDestroy();
    }

    public int getRandomNumber()
    {
        return mGenerator.nextInt(100);
    }

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

    // Client is Unbinding via the unbindService() call
    @Override
    public boolean onUnbind(Intent intent)
    {
        return super.onUnbind(intent);
    }

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

Answer 1

正如我所见，您正在使用 bindService()。

A bound service typically lives only while it serves another application component and does not run in the background indefinitely.

因此，如果您的 Activity (绑定(bind)到服务)完成，则服务将不再运行。

要在后台运行服务，您必须创建带有标志 START_STICKY 的 STICKY 服务。

 @Override
public int onStartCommand(Intent intent, int flags, int startId) {
  // Do your task here
  return START_STICKY;
 }

START_STICKY 服务可以在后台运行而无需任何 Activity 。您可以通过回调与服务通信。

要创建一个粘性服务，请阅读Service .