casting - 为什么ByteData.view(buffer)抛出NoSuchMethodError:类 'String'没有实例方法 'asByteData'

Question

我正在尝试读取UDP数据并将其转换为float。

我知道我需要

从RawDatagramSocket接收数据报

从数据报

中获取ByteBuffer

将ByteBuffer转换为ByteData

在ByteData上使用getFloat32方法

这是损坏的代码:

import 'dart:io';
import 'dart:typed_data';
import 'dart:mirrors';

getTypeName(dynamic obj) {
  return reflect(obj).type.reflectedType.toString();
}

void main(List<String> args){
  RawDatagramSocket.bind("192.168.1.1", 4444).then((RawDatagramSocket socket){
    print('Datagram socket ready to receive');
    print('${socket.address.address}:${socket.port}');
    socket.listen((RawSocketEvent e){
      Datagram d = socket.receive();
      if (d == null) return;
      ByteBuffer buffer = getTypeName(d.data.buffer);
      ByteData bdata = new ByteData.view(buffer);
    });
  });
}

这是调试代码:

import 'dart:io';
import 'dart:typed_data';
import 'dart:mirrors';

getTypeName(dynamic obj) {
  return reflect(obj).type.reflectedType.toString();
}

void main(List<String> args){
  RawDatagramSocket.bind("192.168.1.1", 4444).then((RawDatagramSocket socket){
    print('Datagram socket ready to receive');
    print('${socket.address.address}:${socket.port}');
    socket.listen((RawSocketEvent e){
      Datagram d = socket.receive();
      if (d == null) return;
      print(d.data);
    });
  });
}

如果我使用以下命令nc -u 192.168.1.1 4444初始化netcat并发送数据“1111”，则会从调试代码中打印出以下内容:

[49, 49, 49, 49, 10]

我知道这些值是assai字符“1111”，后跟回车符。

问题是，当我运行“代码破损”时，最终收到以下消息:

Unhandled exception:
NoSuchMethodError: Class 'String' has no instance method 'asByteData'.
Receiver: "_ByteBuffer"
Tried calling: asByteData(0, null)
#0      Object._noSuchMethod (dart:core-patch/object_patch.dart:43)
#1      Object.noSuchMethod (dart:core-patch/object_patch.dart:47)
#2      new ByteData.view (dart:typed_data:449)
#3      main.<anonymous closure>.<anonymous closure> (file:///Users/iProgram/test.dart:17:25)
#4      _RootZone.runUnaryGuarded (dart:async/zone.dart:1307)
#5      _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:330)
#6      _BufferingStreamSubscription._add (dart:async/stream_impl.dart:257)
#7      _StreamController&&_SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:796)
#8      _StreamController._add (dart:async/stream_controller.dart:667)
#9      _StreamController.add (dart:async/stream_controller.dart:613)
#10     new _RawDatagramSocket.<anonymous closure> (dart:io-patch/socket_patch.dart:1699)
#11     _NativeSocket.issueReadEvent.issue (dart:io-patch/socket_patch.dart:760)
#12     _microtaskLoop (dart:async/schedule_microtask.dart:41)
#13     _startMicrotaskLoop (dart:async/schedule_microtask.dart:50)
#14     _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:99)
#15     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:152)

问题是，当我不使用字符串或asByteData命令时为什么会出现错误Class 'String' has no instance method 'asByteData'？

我一直在使用以下文档:Dart - ByteData

谢谢

Answer 1

why am I getting the error Class 'String' has no instance method 'asByteData' when I am not using a string or the asByteData command?

调用堆栈显示了这里发生的事情:

Tried calling: asByteData(0, null)
#0      Object._noSuchMethod (dart:core-patch/object_patch.dart:43)
#1      Object.noSuchMethod (dart:core-patch/object_patch.dart:47)
#2      new ByteData.view (dart:typed_data:449)

您正在调用new ByteData.view，而在内部调用asByteData。
ByteData.view构造函数采用ByteBuffer，但您正在将其传递给字符串:

ByteBuffer buffer = getTypeName(d.data.buffer);

尽管您在此处编写了ByteBuffer，但是getTypeName()函数实际上返回的是String:

return reflect(obj).type.reflectedType.toString();