如何修复此错误：Struct 'Utf8' 为空。不推荐支持空结构......改用 Opaque

Question

我最近在运行我的应用程序时开始收到此错误。它似乎不会影响一切，但它在日志中非常嘈杂和烦人。我没有对我的应用程序进行任何更改或添加任何会导致此类问题的内容，我最近所做的唯一一件事就是升级到最新版本的 Flutter（我经常升级，所以距离上次更新只有几天时间） .

../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:1111:7: Info: Struct 'ENUMLOGFONTEX' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class ENUMLOGFONTEX extends Struct {
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2835:7: Info: Struct 'BLUETOOTH_PIN_INFO' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class BLUETOOTH_PIN_INFO extends Struct {
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2960:7: Info: Struct 'EXCEPINFO' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class EXCEPINFO extends Struct {}
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2966:7: Info: Struct 'PROPERTYKEY' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class PROPERTYKEY extends Struct {}
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2973:7: Info: Struct 'PROPVARIANT' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class PROPVARIANT extends Struct {}
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2978:7: Info: Struct 'SAFEARRAY' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class SAFEARRAY extends Struct {}
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2985:7: Info: Struct 'CLSID' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class CLSID extends Struct {}
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2992:7: Info: Struct 'STATSTG' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class STATSTG extends Struct {}
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/win32-1.7.4/lib/src/structs.dart:2999:7: Info: Struct 'NLM_SIMULATED_PROFILE_INFO' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class NLM_SIMULATED_PROFILE_INFO extends Struct {}
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/ffi-0.1.3/lib/src/utf8.dart:23:7: Info: Struct 'Utf8' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class Utf8 extends Struct {
      ^
../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/ffi-0.1.3/lib/src/utf16.dart:16:7: Info: Struct 'Utf16' is empty. Support for empty structs is deprecated and will be removed in the next stable version of Dart. Use Opaque instead.
class Utf16 extends Struct {
      ^

列表中的最后一个错误看起来略有不同：

../../../../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/ffi-0.1.3/lib/src/allocation.dart:47:33: Info: Support for using non-constant type arguments 'T' in this FFI API is deprecated and will be removed in the next stable version of Dart. Rewrite the code to ensure that type arguments are compile time constants referring to a valid native type.
  final int totalSize = count * sizeOf<T>();
                                ^

知道我该如何解决这个问题吗？我试过了，flutter clean但这并没有解决它。

这是我的flutter doctor输出：

Flutter 1.26.0-13.0.pre.190 • channel master • https://github.com/flutter/flutter.git
Framework • revision 7db172b24d (50 minutes ago) • 2021-01-26 17:18:40 -0800
Engine • revision b11bef83a5
Tools • Dart 2.12.0 (build 2.12.0-263.0.dev)

Running flutter doctor...
Doctor summary (to see all details, run flutter doctor -v):
[?] Flutter (Channel master, 1.26.0-13.0.pre.190, on Mac OS X 10.15.7 19H2 darwin-x64, locale en-US)
[?] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
[?] Xcode - develop for iOS and macOS
[?] Chrome - develop for the web
[?] Android Studio (version 4.1)
[?] IntelliJ IDEA Community Edition (version 2020.3.1)
[?] VS Code (version 1.52.1)
[?] Connected device (2 available)

• No issues found!

Answer 1

显然这个flutter SDK版本有一个错误，之前的版本运行良好，你可以在flutter控制台使用这个命令解决这个问题：

flutter downgrade

Answer 2

我在开发频道上遇到了同样的问题。我没有降级就解决了这个问题。只需添加此依赖项：

ffi: ^1.0.0

Answer 3

这对master频道上的用户来说是暂时的。FFI 很快将不允许空Struct对象，而是像Utf8现在这样的类应该从Opaque. 我们正处于 SDK 已升级但package:ffi包尚未更新的过渡阶段，因此如果您在最新master版本上运行，则会显示消息。这些消息应该是非致命的。