使用 ReactiveUI wpf 无法将视图模型中的枚举值列表绑定到视图中的组合框

问题描述

假设我有这个枚举

 public enum LogType
     {
         None = 0,
         File = 1,
         Folder = 2
     }

我有这个组合框

    <ComboBox Name="CustomLogLogType"  FontSize="10"
              MinHeight="20" Height="20" SelectedItem="{Binding LogType}">

然后像这样的 ViewModel

Then a ViewModel like so

public class CustomLogRuleItemViewModel : ReactiveObject
{

    [Reactive]
    public LogType LogType { get; set; } = LogType.File;

    public List<LogType> LogTypes => Enum.GetValues(typeof(LogType)).Cast<LogType>().Where(_ => _ != LogType.None).ToList();
}

然后在视图后面的代码中

Then in code behind for the view

public partial class CustomLogRuleItemView : ReactiveUserControl<CustomLogRuleItemViewModel> 
{
    public CustomLogRuleItemView()
    {
        InitializeComponent();

        this.ViewModel = new CustomLogRuleItemViewModel();
        this.DataContext = this.ViewModel;

        //The below works
        //CustomLogLogType.ItemsSource = this.ViewModel.LogTypes;


        this.WhenActivated(
            disposables =>
            {

                //If I use below it will error with exception
                this.OneWayBind(this.ViewModel,
                        _ => _.LogTypes, _ => _.CustomLogLogType.ItemsSource)
                    .DisposeWith(disposables);
            });
    }
}

基本上如果我在下面绑定它就可以了

Basically if I bind with below it works

CustomLogLogType.ItemsSource = this.ViewModel.LogTypes;

但是如果我尝试使用 ReactiveUI 进行如下绑定

But if i try to use ReactiveUI to do the binding as in below

            this.OneWayBind(this.ViewModel,
                    _ => _.LogTypes, _ => _.CustomLogLogType.ItemsSource)
                .DisposeWith(disposables);

我收到一个异常，指出 ReactiveUI.IViewFor 上的 LogType 违反了类型T"的约束.不确定为什么我会对 IViewFor 产生争论，因为这与视图的 ViewModel 实现有关.

I get an exception stating that LogType on ReactiveUI.IViewFor violates the constraint of type 'T'. Unsure why I would be getting something arguing about IViewFor as that just has to do with the ViewModel implementation for view.

推荐答案

问题是 ReactiveUI 默认会通过解析 IViewFor 来设置 ItemTemplate旨在使您更容易拆分您的视图.因此，如果您在这些场景中添加 ItemTemplate、DisplayMemberPath 或 ItemTemplateSelector，自动视图查找将被关闭.请参阅 norelreferr> 用于执行此操作的代码行.

The issue is that ReactiveUI by default will set a ItemTemplate by resolving for IViewFor<TypeInItemsSource> which is meant to make it easier to split off your views. So the automatic view lookup gets turned off if you add a ItemTemplate, DisplayMemberPath or ItemTemplateSelector in these scenarios. See this code for the line of code that does it.

<ComboBox Name="CustomLogLogType"  FontSize="10"
                  MinHeight="20" Height="20">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding}" />
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>

我可以通过添加自己的 ItemTemplate 来解决这个问题.

I was able to get around it by adding my own ItemTemplate.

我认为这实际上是一个错误，所以如果您不介意在 https 上打开一个错误://github.com/reactiveui/ReactiveUI/issues 我会在接下来的几天内修复它.我不认为我们应该为原始类型添​​加 ItemTemplate，因为实际上我不认为用户真的希望原始类型具有此功能.

I think this is realistically a bug though so if you don't mind opening a bug at https://github.com/reactiveui/ReactiveUI/issues I will put a fix in the next couple days for it. I don't think for primitive types we should be adding a ItemTemplate, since realistically I don't see users realistically wanting this feature for primitive types.

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