WPF ComboBox 在一个 DataTrigger 之后不显示 SelectedItem 但在另一个 DataTrigger 之后显示

Question

所以我有一个组合框，我想为多组数据重复使用，而不是拥有 3 个单独的组合框。也许这很糟糕，有人可以告诉我。我对所有想法和建议持开放态度。我只是想清理一些代码，并认为一个组合框而不是 3 更干净。无论如何，ItemsSource 和 SelectedItem 都应该在另一个 ComboBox'svalue 发生变化时发生变化，这会提高不起作用的 ComboBox 的 Property Changed 值。最糟糕的部分是当CurSetpoint.ActLowerModeIsTimerCondition为真时，它总是正确加载SelectedItem，但是当从那个到CurSetpoint.ActLowerGseMode为真时，组合框没有加载SelectedItem。

这是有问题的 ComboBox 的 XAML。

<ComboBox Grid.Row="1" Grid.Column="1" Margin="5,2" VerticalAlignment="Center" Name="cmbActTimersSetpointsGseVars">
       <ComboBox.Style>
          <Style BasedOn="{StaticResource {x:Type ComboBox}}" TargetType="{x:Type ComboBox}">
             <Style.Triggers>
                <DataTrigger Binding="{Binding Path=CurSetpoint.ActLowerModeIsTimerCondition}" Value="True">
                   <Setter Property="ItemsSource" Value="{Binding TimerInstances}" />
                   <Setter Property="SelectedItem" Value="{Binding CurSetpoint.ActLowerTimerInstance, Mode=TwoWay}" />
                   <Setter Property="DisplayMemberPath" Value="DisplayName"></Setter>
                   <Setter Property="Visibility" Value="Visible" />
                </DataTrigger>
                <DataTrigger Binding="{Binding Path=CurSetpoint.ActLowerGseMode}" Value="True">
                   <Setter Property="ItemsSource" Value="{Binding EnabledGseVars}" />
                   <Setter Property="SelectedItem" Value="{Binding CurSetpoint.ActLowerGseVar, Mode=TwoWay}" />
                   <Setter Property="DisplayMemberPath" Value="DisplayName"></Setter>
                   <Setter Property="Visibility" Value="Visible" />
                </DataTrigger>
                <DataTrigger Binding="{Binding Path=CurSetpoint.ActModeIsLogicCondition}" Value="True">
                   <Setter Property="ItemsSource" Value="{Binding SetpointStates}" />
                   <Setter Property="SelectedItem" Value="{Binding CurSetpoint.ActSetpoint1State, Mode=TwoWay}" />
                   <Setter Property="DisplayMemberPath" Value="Value"></Setter>
                   <Setter Property="Visibility" Value="Visible" />
                </DataTrigger>
                <DataTrigger Binding="{Binding Path=CurSetpoint.ShowActLowerCmbBox}" Value="False">
                   <Setter Property="Visibility" Value="Collapsed" />
                </DataTrigger>
             </Style.Triggers>
          </Style>
       </ComboBox.Style>
</ComboBox>

这是两个组合框的图像。当模式从 Timer 更改为 Variable 时，它​​不会加载任何内容，尽管它的绑定不是 null 并且它的实例和 itemssource 实例数据没有改变。但是如果我从变量转到计时器，计时器：1 会正确显示。

这是模式组合框值被更改后的模型代码。连同其他两个属性，即相关 ComboBox 的 SelectedItems。以及ItemsSource的属性

private VarItem actLowerMode;
public VarItem ActLowerMode
{
   get { return this.actLowerMode; }
   set
   {
      if (value != null)
      {
         var oldValue = this.actLowerMode;

         this.actLowerMode = value;
         config.ActLowerMode.Value = value.ID;

         //if they weren't the same we need to reset the variable name
         //Note: 5/21/19 Needs to be this way instead of before because when changing from Timer->GseVariable it wouldn't change the config value because it
         //thought it was still a timer condition because the value hadn't been changed yet.
         if (oldValue != null && (oldValue.CheckAttribute("timer") != value.CheckAttribute("timer")))
         {
            if (value.CheckAttribute("timer"))
            {
               ActLowerTimerInstance = model.TimerInstances.First();
            }
            else
            {
               ActLowerVarName = "";
               if (GseMode)
               {
                  ActLowerGseVar = model.EnabledGseVars.FirstOrDefault();
               }
            }
         }

         RaisePropertyChanged("ActLowerMode");
         RaisePropertyChanged("HasActLowerScale");
         RaisePropertyChanged("ActLowerGseMode");
         RaisePropertyChanged("HasActLowerVarName");
         RaisePropertyChanged("ActLowerModeIsConstant");
         RaisePropertyChanged("ActLowerRow1Label");
         RaisePropertyChanged("ActLowerModeIsTimerCondition");
         RaisePropertyChanged("ShowActLowerConstTextBox");
         RaisePropertyChanged("ShowActLowerCmbBox");
         RaisePropertyChanged("ShowActLowerRow1Label");
         if (GseMode)
         {
            RaisePropertyChanged("ActLowerGseMode");
         }
      }
   }
}

private GseVariableModel actLowerGseVar;
public GseVariableModel ActLowerGseVar
{
   get { return this.actLowerGseVar; }
   set
   {
      if (value != null)
      {
         this.actLowerGseVar = value;
         if (!ActLowerModeIsTimerCondition)//only changing the config value if its not set to timer
         {
            config.ActLowerVarName.Value = value.Number.ToString();
         }
         RaisePropertyChanged("ActLowerGseVar");
      }
   }
}      

private INumberedSelection actLowerTimerInstance;
public INumberedSelection ActLowerTimerInstance
{
   get { return this.actLowerTimerInstance; }
   set
   {
      if (value != null)
      {
         this.actLowerTimerInstance = value;
         config.ActLowerVarName.Value = value.Number.ToString();
         RaisePropertyChanged("ActLowerTimerInstance");
      }
   }
}

public ObservableCollection<INumberedSelection> TimerInstances { get { return this.timerInstances; } }

public ObservableCollection<GseVariableModel> EnabledGseVars
{
   get 
   {
      return enabledGseVariables; 
   }
}

我确定我可能忽略了一些重要信息，因此我会根据你们的任何问题或需要的详细信息进行更新。

更新：只是想按照赏金中的说明添加。如果我在这里做的不是一个好主意，并且有更好的方法，请有经验的人告诉我为什么以及如何做。如果有更好的方法，而我做的不好，我只需要知道。

Answer 1

绑定多个ComboBoxes并设置它们的Visibility并没有错。一方面，与您帖子中的代码相比，它大大降低了复杂性。

尽管如此，您可以通过在视图模型和视图之间引入额外的抽象来轻松交换ItemsControl 的上下文（不要与DataContext 混淆）。

这就是它的工作原理：

1. 创建具有相关属性的上下文对象
2. 将上下文应用到您的ItemsControl
3. 让 de 属性在 context 更改时重新绑定

您收集每个实体的属性的想法当然是一个好主意。尽管实现可能会更好，但视图模型和视图看起来都很臃肿。这就是上下文对象的全部意义，在您来回交换上下文时收集和保持状态。

从我们的模型类开始。让我们针对接口编写代码（即使 ItemsSource 没有类型）。

namespace WpfApp.Models
{
    public interface IEntity
    {
        string Name { get; }
    }

    public class Dog : IEntity
    {
        public Dog(string breed, string name)
        {
            Breed = breed;
            Name = name;
        }

        public string Breed { get; }
        public string Name { get; }
    }

    public class Author : IEntity
    {
        public Author(string genre, string name)
        {
            Genre = genre;
            Name = name;
        }

        public string Genre { get; }
        public string Name { get; }
    }
}

接下来是 ViewModel，从我们的上下文开始。

namespace WpfApp.ViewModels
{
    public class ItemsContext : ViewModelBase
    {
        public ItemsContext(IEnumerable<IEntity> items)
        {
            if (items == null || !items.Any()) throw new ArgumentException(nameof(Items));

            Items = new ObservableCollection<IEntity>(items);
            SelectedItem = Items.First();
        }

        public ObservableCollection<IEntity> Items { get; }

        private IEntity selectedItem;
        public IEntity SelectedItem
        {
            get { return selectedItem; }
            set
            {
                selectedItem = value;
                OnPropertyChanged();
            }
        }

        public string DisplayMemberPath { get; set; }
    }
}

如前所述，带有SelectedItem 通知的相关属性并没有什么特别之处。我们立即看到对我们的MainViewModel 的影响。

namespace WpfApp.ViewModels
{
    public class MainViewModel : ViewModelBase
    {
        private readonly ItemsContext _dogContext;
        private readonly ItemsContext _authorContext;

        public MainViewModel()
        {
            _dogContext = new ItemsContext(FetchDogs()) { DisplayMemberPath = nameof(Dog.Breed) };
            _authorContext = new ItemsContext(FetchAuthors()) { DisplayMemberPath = nameof(Author.Genre) };
        }

        private ItemsContext selectedContext;
        public ItemsContext SelectedContext
        {
            get { return selectedContext; }
            set
            {
                selectedContext = value;
                OnPropertyChanged();
            }
        }

        private bool dogChecked;
        public bool DogChecked
        {
            get { return dogChecked; }
            set
            {
                dogChecked = value;
                if(dogChecked) SelectedContext = _dogContext;
            }
        }

        private bool authorChecked;
        public bool AuthorChecked
        {
            get { return authorChecked; }
            set
            {
                authorChecked = value;
                if(authorChecked) SelectedContext = _authorContext;
            }
        }

        private static IEnumerable<IEntity> FetchDogs() =>
            new List<IEntity>
            {
                new Dog("Terrier", "Ralph"),
                new Dog("Beagle", "Eddy"),
                new Dog("Poodle", "Fifi")
            };

        private static IEnumerable<IEntity> FetchAuthors() =>
            new List<IEntity>
            {
                new Author("SciFi", "Bradbury"),
                new Author("RomCom", "James")
            };
    }
}

两个完全分离的流，每个流管理自己的上下文。很明显，您可以轻松地将其扩展到任意数量的上下文，而不会相互干扰。现在，要将上下文应用到我们的ItemsControl，我们有两个选项。我们可以继承 Control 或使用附加属性。优先考虑组合而不是继承，这是带有 AP 的类。

namespace WpfApp.Extensions
{
    public class Selector
    {
        public static ItemsContext GetContext(DependencyObject obj) => (ItemsContext)obj.GetValue(ContextProperty);
        public static void SetContext(DependencyObject obj, ItemsContext value) => obj.SetValue(ContextProperty, value);

        public static readonly DependencyProperty ContextProperty =
            DependencyProperty.RegisterAttached("Context", typeof(ItemsContext), typeof(Selector), new PropertyMetadata(null, OnItemsContextChanged));

        private static void OnItemsContextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var selector = (System.Windows.Controls.Primitives.Selector)d;
            var ctx = (ItemsContext)e.NewValue;

            if (e.OldValue != null) // Clean up bindings from previous context, if any
            {
                BindingOperations.ClearBinding(selector, System.Windows.Controls.Primitives.Selector.SelectedItemProperty);
                BindingOperations.ClearBinding(selector, ItemsControl.ItemsSourceProperty);
                BindingOperations.ClearBinding(selector, ItemsControl.DisplayMemberPathProperty);
            }

            selector.SetBinding(System.Windows.Controls.Primitives.Selector.SelectedItemProperty, new Binding(nameof(ItemsContext.SelectedItem)) { Source = ctx, Mode = BindingMode.TwoWay });
            selector.SetBinding(ItemsControl.ItemsSourceProperty, new Binding(nameof(ItemsContext.Items)) { Source = ctx });
            selector.SetBinding(ItemsControl.DisplayMemberPathProperty, new Binding(nameof(ItemsContext.DisplayMemberPath)) { Source = ctx });
        }
    }
}

这涵盖了第 2 步和第 3 步。您可以随意调整它。例如，我们将ItemsContext.DisplayMemberPath 设置为非通知属性，因此您可以直接设置值而不是通过绑定。

最后是视图，所有这些都汇集在一起​​。

<Window x:Class="WpfApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:vm="clr-namespace:WpfApp.ViewModels"
        xmlns:ext="clr-namespace:WpfApp.Extensions"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800" WindowStartupLocation="CenterScreen">
    <Window.DataContext>
        <vm:MainViewModel/>
    </Window.DataContext>
    <Window.Resources>
        <Style x:Key="SelectorStyle" TargetType="{x:Type Selector}">
            <Setter Property="Width" Value="150"/>
            <Setter Property="HorizontalAlignment" Value="Left"/>
            <Setter Property="Margin" Value="0,20"/>
        </Style>
    </Window.Resources>
    <StackPanel Margin="20">
        <RadioButton GroupName="Entities" Content="Dogs" IsChecked="{Binding DogChecked}" />
        <RadioButton GroupName="Entities" Content="Authors" IsChecked="{Binding AuthorChecked}" />
        <ComboBox ext:Selector.Context="{Binding SelectedContext}" Style="{StaticResource SelectorStyle}" />
        <ListBox  ext:Selector.Context="{Binding SelectedContext}" Style="{StaticResource SelectorStyle}" />
        <DataGrid ext:Selector.Context="{Binding SelectedContext}" Style="{StaticResource SelectorStyle}" />
    </StackPanel>
</Window>

附加属性很酷的一点是，我们针对抽象的Selector 控件进行编码，它是ItemsControl 的直接后代。因此，无需更改我们的较低层，我们也可以与 ListBox 和 DataGrid 共享我们的上下文。