是否可以在后台间隔中调用Web服务？

Question

我正在开发一个需要从后台调用Web服务的应用程序。我已经编写了一个代码，但问题是如果Activity被系统销毁（在后台长时间销毁），那么调用就停止了。因为处理程序无法获取Activity实例。我看到许多代码使用各种代码，但没有任何帮助。所以，如果有人帮助我，那么我会感激他。

MyService class:

public class MyService extends Service {
    Callbacks activity;
    private long startTime = 0;
    private long millis = 0;
    private final IBinder mBinder = new LocalBinder();
    Handler handler = new Handler();
    Runnable serviceRunnable = new Runnable() {
        @Override
        public void run() {
        millis = System.currentTimeMillis() - startTime;
        activity.updateClient(millis); //Update Activity (client) by the implementd callback
        handler.postDelayed(this, 5000);
        Log.e("I am here", "++++++++++++++++++++++++++");
    }
};


@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    //Do what you need in onStartCommand when service has been started
    return START_NOT_STICKY;
}

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

//returns the instance of the service
public class LocalBinder extends Binder {
    public MyService getServiceInstance() {
        return MyService.this;
    }
}

//Here Activity register to the service as Callbacks client
public void registerClient(Activity activity) {
    this.activity = (Callbacks) activity;
}

public void startCounter() {
    startTime = System.currentTimeMillis();
    handler.postDelayed(serviceRunnable, 0);
    Toast.makeText(getApplicationContext(), "Counter started", Toast.LENGTH_SHORT).show();
}

public void stopCounter() {
    handler.removeCallbacks(serviceRunnable);
}


//callbacks interface for communication with service clients! 
public interface Callbacks {
    void updateClient(long data);
}

}

MainActivity类：

public class MainActivity extends AppCompatActivity implements     MyService.Callbacks {
    ToggleButton toggleButton;
    ToggleButton tbStartTask;
    TextView tvServiceState;
    TextView tvServiceOutput;
    Intent serviceIntent;
    MyService myService;
    int seconds;
    int minutes;
    int hours;

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

    serviceIntent = new Intent(MainActivity.this, MyService.class);
    setViewsWidgets();
}

private void setViewsWidgets() {
    toggleButton = (ToggleButton) findViewById(R.id.toggleButton);
    toggleButton.setOnClickListener(btListener);
    tbStartTask = (ToggleButton) findViewById(R.id.tbStartServiceTask);
    tbStartTask.setOnClickListener(btListener);
    tvServiceState = (TextView) findViewById(R.id.tvServiceState);
    tvServiceOutput = (TextView) findViewById(R.id.tvServiceOutput);

}

private ServiceConnection mConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName className, IBinder service) {
        Toast.makeText(MainActivity.this, "onServiceConnected called", Toast.LENGTH_SHORT).show();
        // We've binded to LocalService, cast the IBinder and get LocalService instance
        MyService.LocalBinder binder = (MyService.LocalBinder) service;
        myService = binder.getServiceInstance(); //Get instance of your service!
        myService.registerClient(MainActivity.this); //Activity register in the service as client for callabcks!
        tvServiceState.setText("Connected to service...");
        tbStartTask.setEnabled(true);
    }

    @Override
    public void onServiceDisconnected(ComponentName arg0) {
        Toast.makeText(MainActivity.this, "onServiceDisconnected called", Toast.LENGTH_SHORT).show();
        tvServiceState.setText("Service disconnected");
        tbStartTask.setEnabled(false);
    }
};

View.OnClickListener btListener = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        if (v == toggleButton) {
            if (toggleButton.isChecked()) {
                startService(serviceIntent); //Starting the service
                bindService(serviceIntent, mConnection, Context.BIND_AUTO_CREATE); //Binding to the service!
                Toast.makeText(MainActivity.this, "Button checked", Toast.LENGTH_SHORT).show();
            } else {
                unbindService(mConnection);
                stopService(serviceIntent);
                Toast.makeText(MainActivity.this, "Button unchecked", Toast.LENGTH_SHORT).show();
                tvServiceState.setText("Service disconnected");
                tbStartTask.setEnabled(false);
            }
        }

        if (v == tbStartTask) {
            if (tbStartTask.isChecked()) {
                myService.startCounter();
            } else {
                myService.stopCounter();
            }
        }
    }
};

@Override
public void updateClient(long millis) {
    seconds = (int) (millis / 1000) % 60;
    minutes = (int) ((millis / (1000 * 60)) % 60);
    hours = (int) ((millis / (1000 * 60 * 60)) % 24);

    tvServiceOutput.setText((hours > 0 ? String.format("%d:", hours) : "") + ((this.minutes < 10 && this.hours > 0) ? "0" + String.format("%d:", minutes) : String.format("%d:", minutes)) + (this.seconds < 10 ? "0" + this.seconds : this.seconds));
    Toast.makeText(MainActivity.this, "I am here", Toast.LENGTH_SHORT).show();
}

}

从后台销毁应用后，此toast Toast.makeText(MainActivity.this, "I am here", Toast.LENGTH_SHORT).show();未显示。那么它也不会调用Web服务。实际上它不会调用此函数updateClient()。我也试过了Log.e()。