public void Start() {

            NativeNFCManager.AddNDEFReadFinishedListener(OnReadFinished);
            NativeNFCManager.AddNDEFWriteFinishedListener(OnWriteFinished);
            //...

            NativeNFCManager.RequestNDEFWrite(/*whatever message stuf*/);


        }

        private void OnReadFinished(NDEFReadResult result) {
            //whatever
        }

        private void OnWriteFinished(NDEFWriteResult result) {
            //whatever
        }