writeAndRead method Null safety

Future<Uint8List?> writeAndRead(
  1. PrinterDevice device,
  2. Uint8List data,
  3. {Duration timeout = const Duration(milliseconds: 1500)}
)

发送数据到打印机，并等待打印机返回结果 device 打印机设备

Implementation

Future<Uint8List?> writeAndRead(PrinterDevice device, Uint8List data,
    {Duration timeout = const Duration(milliseconds: 1500)}) async {
  var result = read(device).first.timeout(timeout);
  if ((await write(device, data)) == true) {
    return result;
  } else {
    return null;
  }
}