Android在片段和服务之间发送消息
作者：互联网
我有一个带有按钮的片段.单击时,它告诉服务开始轮询传感器,然后将传感器数据插入后台线程的数据库中.当再次按下按钮时,服务将停止.当按下“停止”按钮时,执行者队列中仍可能有一些任务正在插入到数据库中,因此在此期间,我想显示一个进度对话框,并在清除整个队列后将其关闭.带按钮的片段如下所示：
public class StartFragment extends Fragment implements View.OnClickListener {
Button startButton;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_start, container, false);
startButton = (Button) view.findViewById(R.id.startButton);
startButton.setOnClickListener(this);
return view;
}
@Override
public void onClick(View v) {
if (recording has not yet started){
mainActivity.startService(new Intent(mainActivity, SensorService.class));
} else {
//I want to display a progress dialog here when the service is told to stop
//Once all executor task queue is clear, I want to dismiss this dialog
mainActivity.stopService(new Intent(mainActivity, SensorService.class));
}
}
}
首次单击该按钮时,将启动以下服务：
public class SensorService extends Service implements SensorEventListener {
public static final int SCREEN_OFF_RECEIVER_DELAY = 100;
private SensorManager sensorManager = null;
private WakeLock wakeLock = null;
ExecutorService executor;
Runnable insertHandler;
private void registerListener() {
//register 4 sensor listeners (acceleration, gyro, magnetic, gravity)
}
private void unregisterListener() {
sensorManager.unregisterListener(this);
}
public BroadcastReceiver receiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
Log.i(TAG, "onReceive("+intent+")");
if (!intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
return;
}
Runnable runnable = new Runnable() {
public void run() {
Log.i(TAG, "Runnable executing...");
unregisterListener();
registerListener();
}
};
new Handler().postDelayed(runnable, SCREEN_OFF_RECEIVER_DELAY);
}
};
public void onSensorChanged(SensorEvent event) {
//get sensor values and store into 4 different arrays here
//insert into database in background thread
executor.execute(insertHandler);
}
@Override
public void onCreate() {
super.onCreate();
//get sensor manager and sensors here
PowerManager manager = (PowerManager) getSystemService(Context.POWER_SERVICE);
wakeLock = manager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, TAG);
registerReceiver(receiver, new IntentFilter(Intent.ACTION_SCREEN_OFF));
//Executor service and runnable for DB inserts
executor = Executors.newSingleThreadExecutor();
insertHandler = new InsertHandler();
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
super.onStartCommand(intent, flags, startId);
startForeground(Process.myPid(), new Notification());
registerListener();
wakeLock.acquire();
return START_STICKY;
}
@Override
public void onDestroy() {
//Prevent new tasks from being added to thread
executor.shutdown();
try {
//Wait for all tasks to finish before we proceed
while (!executor.awaitTermination(1, TimeUnit.SECONDS)) {
Log.i(TAG, "Waiting for current tasks to finish");
}
} catch (InterruptedException e) {
executor.shutdownNow();
Thread.currentThread().interrupt();
}
if (executor.isTerminated()){
//Stop everything else once the task queue is clear
unregisterReceiver(receiver);
unregisterListener();
wakeLock.release();
dbHelper.close();
stopForeground(true);
//Once the queue is clear, I want to send a message back to the fragment to dismiss the progress dialog here
}
}
class InsertHandler implements Runnable {
public void run() {
//get sensor values from 4 arrays, and insert into db here
}
}
所以我想在按下第二个按钮时显示对话框.然后,一旦再次按下它,服务将停止,我要等到队列清除后再将dismiss事件发送回片段以关闭进度对话框.
显示对话框很容易.我可以在调用stopService之前,在片段的onClick方法中添加进度对话框代码
我在弄清楚如何在SensorService的onDestroy中发送消息以关闭该对话框时遇到了困难
在不借助外部库的情况下实现此目的的最佳方法是什么？
是否可以使用某种方式使用我在SensorService中使用的BroadcastReceiver？还是最好在片段中创建一个新的Handler,然后以某种方式将其传递给服务,以便它可以将消息发送回片段？
编辑：
我已经根据以下答案之一尝试了以下方法：
在我的片段类中添加了MessageHandler类：
public static class MessageHandler extends Handler {
@Override
public void handleMessage(Message message) {
int state = message.arg1;
switch (state) {
case 0:
stopDialog.dismiss();
break;
case 1:
stopDialog = new ProgressDialog(mainActivity);
stopDialog.setMessage("Stopping...");
stopDialog.setTitle("Saving data");
stopDialog.setProgressNumberFormat(null);
stopDialog.setCancelable(false);
stopDialog.setMax(100);
stopDialog.show();
break;
}
}
}
在我的片段中创建了一个新的MessageHandler实例(试图将其放置在多个位置…结果相同)：
public static Handler messageHandler = new MessageHandler();
然后使用以下命令从我的片段启动服务：
Intent startService = new Intent(mainActivity, SensorService.class);
startService.putExtra("MESSENGER", new Messenger(messageHandler));
getContext().startService(startService);
在我的SensorService BroadcastReceiver中,创建messageHandler：
Bundle extras = intent.getExtras();
messageHandler = (Messenger) extras.get("MESSENGER");
然后,在SensorService onDestroy的最开始显示对话框：
sendMessage("SHOW");
并在同一方法的最后将其关闭：
sendMessage("HIDE");
我的sendMessage方法看起来像这样：
public void sendMessage(String state) {
Message message = Message.obtain();
switch (state) {
case "SHOW":
message.arg1 = 1;
break;
case "HIDE" :
message.arg1 = 0;
break;
}
try {
messageHandler.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
这样我就可以启动“服务正常”了,但是当我再次按它停止时,我得到了：
java.lang.RuntimeException：无法停止服务com.example.app.SensorService@21124f0：java.lang.NullPointerException：尝试在虚拟设备上调用虚拟方法’void android.os.Messenger.send(android.os.Message)’空对象引用
及其涉及SensorService.send(message)的SensorService的第105行
关于什么可能是错的想法？
解决方法:
活动中：
protected BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, final Intent intent) {
runOnUiThread(new Runnable() {
@Override
public void run() {
if(intent.hasExtra("someExtraMessage")){
doSomething(intent.getStringExtra("someExtraMessage"));
}
}
});
}
};
@Override
public void onCreate(Bundle savedInstanceState, PersistableBundle persistentState) {
super.onCreate(savedInstanceState, persistentState);
LocalBroadcastManager.getInstance(this).registerReceiver(mMessageReceiver,
new IntentFilter("message-id"));
}
protected void onDestroy() {
super.onDestroy();
LocalBroadcastManager.getInstance(this).unregisterReceiver(mMessageReceiver);
}
public void doSomething(){
//...
}
然后从服务的某个地方：
Context context = BamBamApplication.getApplicationContext(); // Can be application or activity context.
// BamBamApplicaiton extends Application ;)
Intent intent = new Intent("message-id");
intent.putExtra("someExtraMessage", "Some Message :)");
LocalBroadcastManager.getInstance(context).sendBroadcast(intent);
实际上,您从一开始就做错了:)所有服务都在主线程上运行,因此在这里您必须更好地启动所有硬处理以异步任务将其移至后台,否则您将卡住应用程序,否则会突然出现意外情况崩溃.
这是您的异步任务示例,该任务在后台解析json api响应,并按参数键入结果.
class ParseJsonInBackground<T> extends AsyncTask<String, Void, ApiResponseModel<T>> {
private ProcessResponse<T> func;
private Type inClass;
public ParseJsonInBackground(ProcessResponse<T> f, Type inClass){
this.func = f;
this.inClass = inClass;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected ApiResponseModel<T> doInBackground(String... json) {
Gson gson = new Gson();
try {
ApiResponseModel<T> result = (ApiResponseModel<T>) gson.fromJson(json[0], inClass);
return result;
}catch(Exception e){
ApiResponseModel<T> result = new ApiResponseModel<T>();
result.data = null;
result.success = false;
result.error = new ArrayList<>();
result.error.add(new ErrorModel(0, "Parsing error", "Parsing error"));
return result;
}
}
@Override
protected void onPostExecute(ApiResponseModel<T> result) {
Utils.hideLoadingProgress(mContext);
if(result != null && func != null){
if(result.success){
func.onSuccess(result);
}else{
func.onError(result);
}
}
}
}
并示例如何调用：
new ParseJsonInBackground<T>(responseFunc, inClass).execute(json.toString());
注意！ -不要在处理过程中使用任何视图,因为这会阻塞主线程,使数据库处理处于类似的异步任务中,不要经常写入数据库以进行事务记录.
标签：android-handler,android-fragments,android-service,android-dialog,android 来源： https://codeday.me/bug/20191118/2030708.html