如何从ReactApplication中的ReactNativeHost中获取MainActivity (ReactActivity)

import com.facebook.react.ReactActivity;
import com.facebook.react.ReactApplication;
import com.facebook.react.ReactNativeHost;
import com.facebook.react.ReactInstanceManager;
import com.facebook.react.ReactContext;

public class MyReactApplication extends ReactApplication {
    // ...

    private ReactActivity getCurrentReactActivity() {
        ReactNativeHost reactNativeHost = getReactNativeHost();
        ReactInstanceManager reactInstanceManager = reactNativeHost.getReactInstanceManager();
        ReactContext reactContext = reactInstanceManager.getCurrentReactContext();

        if (reactContext != null && reactContext instanceof ReactActivity) {
            return (ReactActivity) reactContext;
        }

        return null;
    }

    // ...
}