Android活动和服务通信：如何保持UI最新

我有一个活动A(不是主要活动),它启动一个服务S,该服务在后台执行一些操作,与此同时,应该对A的UI进行一些更改.

我们只说S计数从0到100,而A应该实时显示此计数.由于S的实际工作非常复杂且占用CPU,因此我不希望使用AsyncTask(实际上,“理想情况下,AsyncTasks应该用于短操作(最多几秒钟).[…]” ),但只有普通的Service在新线程中启动(IntentService也可以).

这是我的活动A：

public class A extends Activity {
    private static final String TAG = "Activity";
    private TextView countTextView;    // TextView that shows the number
    Button startButton;                // Button to start the count
    BResultReceiver resultReceiver;


    /**
     * Receive the result from the Service B.
     */
    class BResultReceiver extends ResultReceiver {
        public BResultReceiver(Handler handler) {
            super(handler);
        }

        @Override
        protected void onReceiveResult(int resultCode, Bundle resultData) {
            switch ( resultCode )  {
                case B.RESULT_CODE_COUNT:
                        String curCount = resultData.getString(B.RESULT_KEY_COUNT);
                        Log.d(TAG, "ResultReceived: " + curCount + "\n");
                        runOnUiThread( new UpdateUI(curCount) );  // NOT WORKING AFTER onResume()!!!
                   break;
            }
        }
    }


    /**
     * Runnable class to update the UI.
     */
    class UpdateUI implements Runnable {
        String updateString;

        public UpdateUI(String updateString) {
            this.updateString = updateString;
        }

        public void run() {
            countTextView.setText(updateString);
        }
    }


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

        countTextView = (TextView) findViewById(R.id.countTextView);
        startButton = (Button) findViewById(R.id.startButton);

        resultReceiver = new BResultReceiver(null);
    }


    public void startCounting(View view) {
        startButton.setEnabled(false);

        //Start the B Service:
        Intent intent = new Intent(this, B.class);
        intent.putExtra("receiver", resultReceiver);
        startService(intent);
    }
}

这是我的服务B：

public class B extends Service {
    private static final String TAG = "Service";
    private Looper serviceLooper;
    private ServiceHandler serviceHandler;
    private ResultReceiver resultReceiver;
    private Integer count;

    static final int RESULT_CODE_COUNT = 100;
    static final String RESULT_KEY_COUNT = "Count";


    /**
     * Handler that receives messages from the thread.
     */
    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            while ( count < 100 ) {
                count++;
                //Sleep...
                sendMessageToActivity(RESULT_CODE_COUNT, RESULT_KEY_COUNT, count.toString());
            }

            //Stop the service (using the startId to avoid stopping the service in the middle of handling another job...):
            stopSelf(msg.arg1);
        }
    }


    @Override
    public void onCreate() {
        //Start up the thread running the service:
        HandlerThread thread = new HandlerThread("ServiceStartArguments", Process.THREAD_PRIORITY_BACKGROUND);
        thread.start();

        this.count = 0;

        //Get the HandlerThread's Looper and use it for our Handler
        serviceLooper = thread.getLooper();
        serviceHandler = new ServiceHandler(serviceLooper);
    }


    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        this.resultReceiver = intent.getParcelableExtra("receiver");

        //For each start request, send a message to start a job and deliver the start ID so we know which request we're stopping when we finish the job:
        Message msg = serviceHandler.obtainMessage();
        msg.arg1 = startId;
        serviceHandler.sendMessage(msg);

        //If we get killed, after returning from here, restart:
        return START_REDELIVER_INTENT;
    }


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


    /**
     * Send a message from to the activity.
     */
    protected void sendMessageToActivity(Integer code, String name, String text) {
        Bundle bundle = new Bundle();
        bundle.putString(name, text);

        //Send the message:
        resultReceiver.send(code, bundle);
    }
}

一切正常,但是如果我单击“后退”按钮(或“主页”按钮),然后重新打开活动A,则A的UI不再更新(它仅显示A的初始配置-即“ startButton”为仍可点击,并且不显示计数-似乎runOnUiThread(…)不再起作用.但是,服务B仍在后台运行,我可以看到正确的计数已传递到Log.d(…)中的活动A.最后,如果我再次单击“ startButton”,则计数不是从开头(0)开始,而是从到达B的位置开始(我已经通过在通知栏中显示它进行了双重检查).

我该如何解决此问题？我希望这样,当我重新打开活动A时,它会自动继续从服务B接收和更新数据.换句话说,服务会保持活动A的UI为最新.

请给我一些提示,链接或一段代码.谢谢！

解决方法:

当您单击后退按钮时,您的活动被破坏.再次启动活动时,您将获得一个新的活动.旋转设备时也会发生这种情况.这是Android lifecycle event

该活动不利于繁重的业务逻辑,仅显示填充/控制stuf.
您需要做的是创建一个简单的MVCModel View Controller.视图(Activity)仅应用于显示结果和控制事件流.

服务可以保存一个数组,当您的Activity启动时,它将onBind()您正在运行的Service(或者如果未运行,则由于您绑定到该服务而启动了Service)让Activity(View)获取结果数组并显示出来.此简单设置不包括(M)Model业务逻辑.

更新资料
继续阅读此书,这是Android的官方文档,并且因为它确实可以满足您的要求,因此是一个完美的开始.如在onStart()中的示例中所见,Activity与服务建立了连接,而在onStop()中,该连接被删除了. onStop()之后没有任何连接.就像您要的一样.我会使用此设置,而不是让Service连续发送数据,因为这会浪费资源,并且Activity不会一直在侦听,因为它将在后台停止.
Here’s an activity that binds to LocalService and calls getRandomNumber() when a button is clicked:

标签：android-handler,android-service,android-activity,android-ui,android
来源： https://codeday.me/bug/20191122/2062439.html