我有一个Activity A（不是主 Activity），它启动一个Service S，它在后台做一些事情，同时，应该对 A 的 UI 进行一些更改。
假设S 从 0 计数到 100并且A 应该在 Real-Time 中显示这个计数。由于 S 的实际工作相当复杂且占用 CPU 资源，因此我不想为其使用AsyncTask（事实上，“AsyncTasks 应该理想地用于短操作（最多几秒钟。）[...]” ) 但只是在一个新线程中启动了一个常规服务（一个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，但如果我单击后退按钮（或主页按钮）然后我重新打开 Activity A，则 A 的 UI 不再更新（它只显示 A 的初始配置 - 即“startButton”是仍然可点击并且未显示计数 - 似乎runOnUiThread(...)不再工作了）。但是，服务 B 仍在后台运行，我可以看到正确的计数被传递给Log.d(...)中的活动A。最后，如果我再次单击“startButton”，则计数不会从开头 (0) 开始，而是从 B 到达的位置开始（我通过在通知栏中显示它来仔细检查它）。
我该如何解决这种行为？我希望，当我重新打开 Activity A 时，它会自动继续从 Service B 接收和更新数据。或者，换句话说，Service 会使 Activity A 的 UI 保持最新。
请给我一些提示、链接或代码。谢谢！