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

问题描述

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，当另一个值发生更改时，所有内容都应该更改，ItemsSource这会提高不起作用的 ComboBox 的 Property Changed 值。最糟糕的是，当它为真时，它总是正确加载，但是当从那个变为真时，组合框没有加载。SelectedItemComboBox'sCurSetpoint.ActLowerModeIsTimerConditionSelectedItemCurSetpoint.ActLowerGseModeSelectedItem

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。

这是模式组合框的值被更改后的模型代码。连同其他两个SelectedItems用于相关组合框的属性。连同属性ItemsSource

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对其进行更新。

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。如果有更好的方法并且我正在做的事情很糟糕，我只需要知道。

标签： c#wpfselecteditemdatatriggeritemssource

解决方案

绑定多个ComboBoxes 并设置它们的Visibility. 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地交换上下文（不要与混淆DataContext）。ItemsControl

这是它的工作原理：

创建具有相关属性的上下文对象
将上下文应用到您的ItemsControl
让 de 属性在上下文改变时重新绑定

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。这就是这个上下文对象的全部意义，在你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，带有通知的相关属性，SelectedItem没什么特别的。我们立即看到对我们的影响MainViewModel。

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")
            };
    }
}

两个干净分离的流，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，要将上下文应用于我们的，ItemsControl我们有两个选择。我们可以继承我们的Control或使用附加属性。喜欢组合而不是继承，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，我们制作ItemsContext.DisplayMemberPath了一个非通知属性，因此您可以直接设置值而不是通过绑定。

最后是视图，这一切都汇集在一起。

<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>

附加属性最酷的地方在于我们针对抽象Selector控件进行编码，它是ItemsControl. ListBox因此，在不改变我们的较低层的情况下，我们也可以共享我们的上下文DataGrid。

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

问题描述

解决方案

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