已解决：Error: The non-abstract class 'InternalSelectableMathState'

Flutter 版本更新后报错了，（还好有个stackoverflow，这里有好多解决方案，我也是用他们的方式来解决了）

报错内容

../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/flutter_math_fork-0.3.3+1/lib/src/widgets/selectable.dart:407:7: Error: The non-abstract class 'InternalSelectableMathState' is missing implementations for these members:
 - TextSelectionDelegate.copySelection
 - TextSelectionDelegate.cutSelection
 - TextSelectionDelegate.pasteText
 - TextSelectionDelegate.selectAll
Try to either
 - provide an implementation,
 - inherit an implementation from a superclass or mixin,
 - mark the class as abstract, or
 - provide a 'noSuchMethod' implementation.

class InternalSelectableMathState extends State
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^
/C:/desarrollo/flutter/packages/flutter/lib/src/services/text_input.dart:985:8: Context: 'TextSelectionDelegate.copySelection' is defined here.
  void copySelection(SelectionChangedCause cause);
       ^^^^^^^^^^^^^
/C:/desarrollo/flutter/packages/flutter/lib/src/services/text_input.dart:965:8: Context: 'TextSelectionDelegate.cutSelection' is defined here.
  void cutSelection(SelectionChangedCause cause);
       ^^^^^^^^^^^^
/C:/desarrollo/flutter/packages/flutter/lib/src/services/text_input.dart:973:16: Context: 'TextSelectionDelegate.pasteText' is defined here.
  Future pasteText(SelectionChangedCause cause);
               ^^^^^^^^^
/C:/desarrollo/flutter/packages/flutter/lib/src/services/text_input.dart:979:8: Context: 'TextSelectionDelegate.selectAll' is defined here.
  void selectAll(SelectionChangedCause cause);
       ^^^^^^^^^


FAILURE: Build failed with an exception.

* Where:
Script 'C:\desarrollo\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 1070

* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command 'C:\desarrollo\flutter\bin\flutter.bat'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 8m 5s
Exception: Gradle task assembleDebug failed with exit code 1

这是因为我用的provider版本是5.0；（不能使用6.0，因为本项目的sdk版本不支持），如果你的sdk>=2.0的话你改一下provider的版本，可能会解决；

解决方式

• provider 版本升级到6.x
• flutter_math_fork 版本升级到 ^0.5.0
• 第三种方式 原文
  
  截屏2022-01-25 下午2.41.56.png

首先尝试将您更新flutter_math_fork到 0.6.0 但在我的情况下
将颤振版本更新到 2.8.1 后我遇到了同样的错误，我无法更新flutter_math_fork到最新版本，因为我正在使用Provider version 5.0.0和flutter_math_formrequire provider version 6.0.0+。因此，在升级其他库之前，您可以修改/lib/src/widgets/selectable.dart此文件。添加这一行。

 @override
  dynamic noSuchMethod(Invocation invocation) {
    // We override noSuchMethod since we do not have concrete implementations
    // for all methods of the selection manager mixins.
    throw NoSuchMethodError.withInvocation(this, invocation);
  }

去掉这个方法

@override  
  void bringIntoView(TextPosition position) {}  
  @override 
  void userUpdateTextEditingValue(  
      TextEditingValue value, SelectionChangedCause cause) {}   
}