System.NotSupportedException：“常量”类型的表达式不受支持您是否错过了表达式中的成员访问前缀？

如何解决System.NotSupportedException：“常量”类型的表达式不受支持您是否错过了表达式中的成员访问前缀？

我在基于 ReactiveUI 的 viewmodel 中收到以下异常...

System.NotSupportedException：不支持的类型表达式 '持续的'。您是否错过了表达式中的成员访问前缀？

错误发生在 ValidationEditorDocumentviewmodel 的构造函数中，在一个可观察的管道中，该管道旨在监视另一个 Reactive viewmodel (SelectedValidatorClientviewmodel) 中的属性 (SelectedValidatorClientviewmodel) 的变化>ValidationEditorviewmodel).

我想要做的是，只要 ValidationEditorviewmodel.SelectedValidatorClientviewmodel 属性发生变化，然后在另一个 viewmodel (RuleEditorviewmodel) 上设置 SelectedValidator。

using NextWare.ProductPortalUI.RXviewmodels.RXviewmodels.ValidationEditor;
using ReactiveUI;
using System;

namespace NextWare.ProductPortalUI.RXviewmodels.ValidationEditor
{
    public sealed partial class ValidationEditorDocumentviewmodel: ReactiveObject 
    {
 
        private ValidatorEditorviewmodel _validationEditorviewmodel;
        private RuleEditorviewmodel _ruleEditorviewmodel;
      
        public ValidationEditorDocumentviewmodel() 
        {
            var setValidatorRuleSet = this.WhenAnyValue(x => ValidationEditorviewmodel.SelectedValidatorClientviewmodel)
                .Subscribe(_ => SetValidatorOnRuleSet());
        }

        private void SetValidatorOnRuleSet()
        {
            if(RuleEditorviewmodel != null)
            {
                RuleEditorviewmodel.SelectedValidator = _validationEditorviewmodel.SelectedValidatorClientviewmodel.Validator;
            }
        }

        public ValidatorEditorviewmodel ValidationEditorviewmodel
        {
            get => _validationEditorviewmodel;
            set => this.RaiseAndSetIfChanged(ref _validationEditorviewmodel,value,nameof(ValidationEditorviewmodel));
        }
 
    }
}

这是引用的viewmodel ...

using NextWare.Domain.ValidationServices.Validator.Clientviewmodels;
using NextWare.ProductPortalUI.SharedComponents.DomainMetaExplorer.Models;
using ReactiveUI;
using Splat;
using System;
 

namespace NextWare.ProductPortalUI.RXviewmodels.RXviewmodels.ValidationEditor
{
    public sealed partial class ValidatorEditorviewmodel : ReactiveObject 
    {
        private ValidatorsClientviewmodel _validatorsClientviewmodel; // Contructor Injected Domain-based viewmodel
        private ValidatorClientviewmodel _selectedValidatorClientviewmodel;
        private Guid _selectedDomainElementModelReferenceId = Guid.NewGuid();
        private TreeNode _selectedMetaExplorerTreeNode;

        public ValidatorEditorviewmodel(ValidatorsClientviewmodel validatorsClientviewmodel = null)
        {
            _validatorsClientviewmodel = validatorsClientviewmodel ?? Locator.Current.GetService<ValidatorsClientviewmodel>();
            
            this.WhenAnyValue(x => x.SelectedValidatorClientviewmodel)
                          .Subscribe(_ => SetValidator());

            this.WhenAnyValue(x => x.SelectedMetaExplorerTreeNode)  // Happens only once at startup
                        .Subscribe(_ => SetValidator());
            
        }

        private void SetValidator()
        {
            if(SelectedValidatorClientviewmodel != null && SelectedMetaExplorerTreeNode != null)
            {
                SelectedValidatorClientviewmodel.Validator.DomainElementName = SelectedMetaExplorerTreeNode.ModelMetaData.Name;
                SelectedValidatorClientviewmodel.Validator.DomainElementNameSpace = SelectedMetaExplorerTreeNode.ModelMetaData.FqviewmodelName;
                SelectedValidatorClientviewmodel.Validator.DomainElementModelReferenceId = SelectedMetaExplorerTreeNode.ModelMetaData.ModelReferenceId;
                SelectedValidatorClientviewmodel.Validator.AggregateRootModelReferenceId = SelectedMetaExplorerTreeNode.ParentModelMetaData.ModelReferenceId;
            }
        }

        public ValidatorsClientviewmodel ValidatorsClientviewmodel
        {
            get => _validatorsClientviewmodel;
            private set => this.RaiseAndSetIfChanged(ref _validatorsClientviewmodel,nameof(ValidatorsClientviewmodel));
        }
              
        public ValidatorClientviewmodel SelectedValidatorClientviewmodel
        {
            get => _selectedValidatorClientviewmodel;
            set => this.RaiseAndSetIfChanged(ref _selectedValidatorClientviewmodel,nameof(SelectedValidatorClientviewmodel));
        }
        public TreeNode SelectedMetaExplorerTreeNode
        {
            get => _selectedMetaExplorerTreeNode;
            set => this.RaiseAndSetIfChanged(ref _selectedMetaExplorerTreeNode,nameof(SelectedMetaExplorerTreeNode));
        }
    }
}

从文档中，WhenAnyValue 从 IObservableChanged 中提取值，据我所知，只有在 ValidationEditorviewmodel 不为空时才会通过，无论 SelectedValidatorClientviewmodel 是否为空。

我很困惑为什么会抛出这个异常。

解决方法

正如 Anthony 在评论中提到的

改变

var setValidatorRuleSet = this.WhenAnyValue(x => ValidationEditorViewModel.SelectedValidatorClientViewModel)
                .Subscribe(_ => SetValidatorOnRuleSet());

到

var setValidatorRuleSet = this.WhenAnyValue(x => x.ValidationEditorViewModel.SelectedValidatorClientViewModel)
                .Subscribe(_ => SetValidatorOnRuleSet());

在 x 之前加上额外的 ValidationEditorViewModel。

WhenAnyValue 依赖于您拥有从“x”到您的财产的 lambda。