integrate printer sdk into flutter

Question

firstly I hit the button to execute openPort and it works successfully,

then I hit the button to execute setPort and it works successfully,

then when I hit the button to run printText the app crashes and it doesn't give any errors

I got no idea why it doesn't work

  int openPort(String text) {
    var openPrn = AppManager.helloLib.lookupFunction<
        ffi.Int Function(ffi.Pointer<Utf8>),
        int Function(Pointer<Utf8>)>('Port_OpenUSBIO');
    var result = openPrn(text.toNativeUtf8());
    return result;
  }

  bool setPort(int num) {
    var setPortt = AppManager.helloLib
        .lookupFunction<ffi.Bool Function(ffi.Int32), bool Function(int)>(
            'Port_SetPort');
    var result = setPortt(num);
    return result;
  }



  bool printText(String text, int nLan, int nOrgx, int nWidthTimes,
      int nHeightTimes, int fontType, int nFontStyle) {
    Uint16List data = Uint16List.fromList(text.codeUnits);
    print(data);
    final dataBtr = calloc<Uint16>(data.length);
    dataBtr.asTypedList(data.length).setAll(0, data);
    print(dataBtr);
    // return true;
    var printTextt = AppManager.helloLib.lookupFunction<
        ffi.Bool Function(
      ffi.Pointer<Uint16>,
      ffi.Int,
      ffi.Int,
      ffi.Int,
      ffi.Int,
      ffi.Int,
      ffi.Int,
    ),
        bool Function(
            Pointer<Uint16>, int, int, int, int, int, int)>('Pos_Text');
    var result = printTextt(
      dataBtr,
      nLan,
      nOrgx,
      nWidthTimes,
      nHeightTimes,
      fontType,
      nFontStyle,
    );
    print(result);
    return result;
  }