作者大大，flutter3发布了，希望适配一下

同求，系统的这个变成私有的了，没法在外面判断了
  /// The current [WidgetsBinding], if one has been created.
  ///
  /// Provides access to the features exposed by this mixin. The binding must
  /// be initialized before using this getter; this is typically done by calling
  /// [runApp] or [WidgetsFlutterBinding.ensureInitialized].
  static WidgetsBinding get instance => BindingBase.checkInstance(_instance);
  static WidgetsBinding? _instance;

  /// A method that shows a useful error message if the given binding
  /// instance is not initialized.
  ///
  /// See [initInstances] for advice on using this method.
  ///
  /// This method either returns the argument or throws an exception.
  /// In release mode it always returns the argument.
  ///
  /// The type argument `T` should be the kind of binding mixin (e.g.
  /// `SchedulerBinding`) that is calling the method. It is used in
  /// error messages.
  @protected
  static T checkInstance<T extends BindingBase>(T? instance) {
    assert(() {
      if (_debugInitializedType == null && instance == null) {
        throw FlutterError.fromParts(<DiagnosticsNode>[
          ErrorSummary('Binding has not yet been initialized.'),
          ErrorDescription('The "instance" getter on the $T binding mixin is only available once that binding has been initialized.'),
          ErrorHint(
            'Typically, this is done by calling "WidgetsFlutterBinding.ensureInitialized()" or "runApp()" (the '
            'latter calls the former). Typically this call is done in the "void main()" method. The "ensureInitialized" method '
            'is idempotent; calling it multiple times is not harmful. After calling that method, the "instance" getter will '
            'return the binding.',
          ),
          ErrorHint(
            'In a test, one can call "TestWidgetsFlutterBinding.ensureInitialized()" as the first line in the test\'s "main()" method '
            'to initialize the binding.',
          ),
          ErrorHint(
            'If $T is a custom binding mixin, there must also be a custom binding class, like WidgetsFlutterBinding, '
            'but that mixes in the selected binding, and that is the class that must be constructed before using the "instance" getter.',
          ),
        ]);
      }
      if (instance == null) {
        assert(_debugInitializedType == null);
        throw FlutterError.fromParts(<DiagnosticsNode>[
          ErrorSummary('Binding mixin instance is null but bindings are already initialized.'),
          ErrorDescription(
            'The "instance" property of the $T binding mixin was accessed, but that binding was not initialized when '
            'the "initInstances()" method was called.',
          ),
          ErrorHint(
            'This probably indicates that the $T mixin was not mixed into the class that was used to initialize the binding. '
            'If this is a custom binding mixin, there must also be a custom binding class, like WidgetsFlutterBinding, '
            'but that mixes in the selected binding. If this is a test binding, check that the binding being initialized '
            'is the same as the one into which the test binding is mixed.',
          ),
          ErrorHint(
            'It is also possible that $T does not implement "initInstances()" to assign a value to "instance". See the '
            'documentation of the BaseBinding class for more details.',
          ),
          ErrorHint(
            'The binding that was initialized was of the type "$_debugInitializedType". '
          ),
        ]);
      }
      try {
        assert(instance != null);
        if (instance._debugConstructed && _debugInitializedType == null) {
          throw FlutterError.fromParts(<DiagnosticsNode>[
            ErrorSummary('Binding initialized without calling initInstances.'),
            ErrorDescription('An instance of $T is non-null, but BindingBase.initInstances() has not yet been called.'),
            ErrorHint(
              'This could happen because a binding mixin was somehow used outside of the normal binding mechanisms, or because '
              'the binding\'s initInstances() method did not call "super.initInstances()".',
            ),
            ErrorHint(
              'This could also happen if some code was invoked that used the binding while the binding was initializing, '
              'for example if the "initInstances" method invokes a callback. Bindings should not invoke callbacks before '
              '"initInstances" has completed.',
            ),
          ]);
        }
        if (!instance._debugConstructed) {
          // The state of _debugInitializedType doesn't matter in this failure mode.
          throw FlutterError.fromParts(<DiagnosticsNode>[
            ErrorSummary('Binding did not complete initialization.'),
            ErrorDescription('An instance of $T is non-null, but the BindingBase() constructor has not yet been called.'),
            ErrorHint(
              'This could also happen if some code was invoked that used the binding while the binding was initializing, '
              "for example if the binding's constructor itself invokes a callback. Bindings should not invoke callbacks "
              'before "initInstances" has completed.',
            ),
          ]);
        }
      } on NoSuchMethodError {
        throw FlutterError.fromParts(<DiagnosticsNode>[
          ErrorSummary('Binding does not extend BindingBase'),
          ErrorDescription('An instance of $T was created but the BindingBase constructor was not called.'),
          ErrorHint(
            'This could happen because the binding was implemented using "implements" rather than "extends" or "with". '
            'Concrete binding classes must extend or mix in BindingBase.',
          ),
        ]);
      }
      return true;
    }());
    return instance!;
  }
Im-Kevin / cool_ui

作者大大，flutter3发布了，希望适配一下 #80
