System.NotSupportedException：不支持类型为"Constant"的表达式。是否错过了表达式中的成员访问前缀？

Question

我在一个基于ReactiveUI的ViewModel中收到以下异常…

系统。NotSupportedException:不支持的类型表达式"常数"。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(SelectedValidatorClientViewModel))在另一个响应式ViewModel (ValidationEditorViewModel)中) .

我想做的是，任何时候ValidationEditorViewModel。如果要更改SelectedValidatorClientViewModel属性，则设置SelectedValidator在另一个ViewModel (RuleEditorViewModel)) .

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));
}

}
}

这是被引用的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, value, nameof(ValidatorsClientViewModel));
}

public ValidatorClientViewModel SelectedValidatorClientViewModel
{
get => _selectedValidatorClientViewModel;
set => this.RaiseAndSetIfChanged(ref _selectedValidatorClientViewModel, value, nameof(SelectedValidatorClientViewModel));
}
public TreeNode SelectedMetaExplorerTreeNode
{
get => _selectedMetaExplorerTreeNode;
set => this.RaiseAndSetIfChanged(ref _selectedMetaExplorerTreeNode, value, nameof(SelectedMetaExplorerTreeNode));
}
}
}

从文档中，WhenAnyValue从IObservableChanged<TSender,>因此，据我所知，如果ValidationEditorViewModel不为空，无论SelectedValidatorClientViewModel是否为空，都只会有一个tick through。

我很困惑为什么会抛出这个异常。

Answer 1

正如Anthony在评论中提到的

改变

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

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

ValidationEditorViewModel前加x

WhenAnyValue依赖于你有一个lambda从'x'到你的属性。