Only one callback can be registered for a function in its own module.

Question

I recently added my own module for Android, which listens for the time zone, and time changes the broadcasts from the system and allows the application to perform some operations. The native module is as follows:

public class TimezoneHandlerModule extends ReactContextBaseJavaModule {
    private final Context context;
    private final TimezoneChangeBroadcastReceiver timezoneChangeBroadcastReceiver;
    private Callback onTimezoneChangeCallback;

    public TimezoneHandlerModule(ReactApplicationContext reactContext) {
        super(reactContext);
        this.context = reactContext;
        this.timezoneChangeBroadcastReceiver = new TimezoneChangeBroadcastReceiver();
    }

    private void registerForTimezoneChangeHandler() {
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(Intent.ACTION_TIME_CHANGED);
        intentFilter.addAction(Intent.ACTION_TIMEZONE_CHANGED);
        getReactApplicationContext().registerReceiver(timezoneChangeBroadcastReceiver, intentFilter);
    }

    private void unregisterTimezoneChangeHandler() {
        getReactApplicationContext().unregisterReceiver(timezoneChangeBroadcastReceiver);
    }

    public void setOnTimezoneChangeCallback(Callback onTimezoneChangeCallback) {
        this.onTimezoneChangeCallback = onTimezoneChangeCallback;
    }

    /**
     * @return the name of this module. This will be the name used to {@code require()} this module
     * from javascript.
     */
    @Override
    public String getName() {
        return "TimezoneHandler";
    }

    @ReactMethod
    public void start(Callback onChange) {
        Log.d(getName(), "Starting the timezone change handler");
        this.registerForTimezoneChangeHandler();
        this.setOnTimezoneChangeCallback(onChange);
    }

    @ReactMethod
    public void stop() {
        Log.d(getName(), "Stopping the timezone change handler");
        this.unregisterTimezoneChangeHandler();
    }

    private class TimezoneChangeBroadcastReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            Log.d(getName(), "Received broadcast for timezone/time change " + intent.getAction());
            final String action = intent.getAction();

            if (action.equals(Intent.ACTION_TIME_CHANGED) || action.equals(Intent.ACTION_TIMEZONE_CHANGED)) {
                TimezoneHandlerModule.this.onTimezoneChangeCallback.invoke();
            }
        }
    }
}

The two response methods are startand stop. startaccepts a function as a parameter that is called whenever a broadcast is received to change the time zone or change the time. After connecting my own module and running the application in the emulator, I opened Settingsand changed the time zone, and I see that the corresponding logs are printed.

11-24 17:07:21.837 1597-1597/com.xyz D/TimezoneHandler: Received broadcast for timezone/time change
11-24 17:07:21.837 1597-1907/com.xyz I/ReactNativeJS: Detected timezone change

When I change the time zone again, I see below error in logcat output

1-24 17:22:42.356 1597-1597/com.galarmapp D/TimezoneHandler: Received broadcast for timezone/time change
11-24 17:22:42.365 1597-1907/com.galarmapp E/ReactNativeJS: The callback start() exists in module TimezoneHandler, but only one callback may be registered to a function in a native module.
11-24 17:22:42.367 1597-1908/com.galarmapp E/unknown:React: The callback start() exists in module TimezoneHandler, but only one callback may be registered to a function in a native module., stack:
                                                            __invokeCallback@12814:10
                                                            <unknown>@12685:24
                                                            guard@12604:3
                                                            invokeCallbackAndReturnFlushedQueue@12684:6

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Answer 1

http://facebook.imtqy.com/react-native/docs/native-modules-android.html#callbacks - " . ". , invoke() , .

javascript. . http://facebook.imtqy.com/react-native/docs/native-modules-android.html#sending-events-to-javascript