Flutter - try catch 块在 SocketException 上不起作用答案

【问题标题】：Flutter - The try catch block doesn't work on SocketExceptionFlutter - try catch 块在 SocketException 上不起作用
【发布时间】：2022-01-11 08:34:13
【问题描述】：

代码在这里：

try {
      final InternetAddress targetAddress = InternetAddress("255.255.255.255");
      _udpSocket.send(utf8.encode("hello"), targetAddress, 8889);
    } on SocketException catch (e) {
      print("on");
    } catch (e, r) {
      print("catch");
    } finally {
      print("hahah");
    }
  }

我想捕捉这个异常。但是，它没有捕捉到这个异常。 并在控制台中引发异常日志：

[VERBOSE-2:ui_dart_state.cc(209)] Unhandled Exception: SocketException: Send failed (OS Error: Can't assign requested address, errno = 49), address = 0.0.0.0, port = 8889
#0      _NativeSocket.send (dart:io-patch/socket_patch.dart:1205:34)
#1      _RawDatagramSocket.send (dart:io-patch/socket_patch.dart:2438:15)
#2      ConnectionManager._sendDetectDevicesDataPocket (package:drop/sdk/connection_manager.dart:98:16)
#3      ConnectionManager.startDetectingDevices (package:drop/sdk/connection_manager.dart:77:5)
<asynchronous suspension>

那么我怎样才能捕捉到这个异常？？？

颤振医生：

[✓] Flutter (Channel stable, 2.8.1, on macOS 12.2 21D5025f darwin-x64, locale
    zh-Hans-CN)
[!] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    ✗ cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.
    ✗ Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/macos#android-setup for
      more details.
[✓] Xcode - develop for iOS and macOS (Xcode 13.2.1)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2020.3)
[☠] IntelliJ IDEA Ultimate Edition (the doctor check crashed)
    ✗ Due to an error, the doctor check did not complete. If the error message
      below is not helpful, please let us know about this issue at
      https://github.com/flutter/flutter/issues.
    ✗ FormatException: Unexpected extension byte (at offset 5)
[✓] VS Code (version 1.62.2)
[✓] Connected device (3 available)

【问题讨论】：

标签： android ios flutter

【解决方案1】：

我找到了原因。我用来发送数据的RawDatagramSocket是我绑定监听数据的udp。当我创建一个新的RawDatagramSocket 来发送数据时，SocketException 消失了。

// error
_udpSocket =
        await RawDatagramSocket.bind(InternetAddress.anyIPv4, _multicastPort, reuseAddress: true, reusePort: true);
_udpSocket.broadcastEnabled = true;
_udpSocket.listen((event) {
xxxxxx
})
_udpSocket.send()

/// works fine when create a new udp
_udpSocket =
        await RawDatagramSocket.bind(InternetAddress.anyIPv4, _multicastPort, reuseAddress: true, reusePort: true);
    _udpSocket.broadcastEnabled = true;
    _udpSocket.listen((event) {})

 final RawDatagramSocket udp = await RawDatagramSocket.bind(InternetAddress.anyIPv4, 0);
    udp.broadcastEnabled = true;
    udp.send(utf8.encode(modelJson), _hotpotAddress, _multicastPort);
    udp.close()

【讨论】：

【解决方案2】：

这对我有用：

import 'dart:io';
...
try {
  final result = await InternetAddress.lookup('example.com');
  if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
    print('connected');
  }
} on SocketException catch (_) {
  print('not connected');
}

【讨论】：