on method
Implementation
VoidCallback on(String method, Handler handler) {
final nativeMessageHandlers = _nativeMessageHandlers[method] ?? <Handler>[];
nativeMessageHandlers.add(handler);
_nativeMessageHandlers[method] = nativeMessageHandlers;
return () {
final nativeMessageHandlers = _nativeMessageHandlers[method] ?? <Handler>[];
nativeMessageHandlers.remove(handler);
};
}