Question

我试图创建一个UserControl来显示一个ListBox（我想稍后将其绑定到视图模型中的一个集合），这样每个项目都会显示在一个ComboBox中（允许其下拉菜单）打开并选择不同的值）。我还想确保不能选择两次值，并且我想添加一个按钮来创建其他列表项。

我的想法是让ListBox的每个DataTemplate在其资源中包含一个CollectionViewSource，对其进行过滤，然后将组合框绑定到过滤后的值。我的问题是我不明白如何在这种情况下让绑定工作 - 一切正常，只要我的绑定是单向的，但是我让ComboBoxes双向绑定的那一刻我得到了一个例外告诉我，我需要为双向绑定设置一个路径才能工作。

我的XAML（为清晰起见略有删节）：

<UserControl x:yadayada x:Name="MultiSelectList">
<Grid>
    <ListBox ItemsSource="{Binding ElementName=MultiSelectList, Path=ChosenItems, Mode=TwoWay}">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <ComboBox Loaded="FrameworkElement_OnLoaded" DropDownOpened="ComboBox_OnDropDownOpened">
                    <ComboBox.Resources>
                        <CollectionViewSource Source="{Binding ElementName=MultiSelectList, Path=AllItems}" x:Key="Src" />
                    </ComboBox.Resources> 
                    <ComboBox.ItemsSource>
                        <Binding Source="{StaticResource Src}" />
                    </ComboBox.ItemsSource>
                </ComboBox>
                <!-- uncommenting the following line crashes the program -->
                <!-- <ComboBox.SelectedValue><Binding></Binding></ComboBox.SelectedValue> -->
            </DataTemplate> 
        </ListBox.ItemTemplate>
    </ListBox>
    <Button Content="New" Click="NewButton_Pressed"/>
</Grid>

背后的代码：

using System;
using System.Collections.ObjectModel;
using System.Linq;
using System.Windows;
using System.Windows.Controls;

namespace WPFCentralOffice.UserControls
{
    public class Element : IEquatable<Element>
    {
        public int ID { get; set; }
        public string Caption { get; set; }

        public bool Equals(Element other)
        {
            return ID == other.ID;
        }

        public override string ToString()
        {
            return ID + " " + Caption;
        }
    }

    public partial class MultiSelectListUserControl : UserControl
    {
        public ObservableCollection<Element> ChosenItems
        {
            get { return (ObservableCollection<Element>)GetValue(ChosenItemsProperty); }
            set { SetValue(ChosenItemsProperty, value); }
        }

        public ObservableCollection<Element> AllItems
        {
            get { return (ObservableCollection<Element>)GetValue(AllItemsProperty); }
            set { SetValue(AllItemsProperty, value); }
        }

        public static DependencyProperty AllItemsProperty = DependencyProperty.Register(
            "AllItems",
            typeof(ObservableCollection<Element>),
            typeof(MultiSelectListUserControl));

        public static DependencyProperty ChosenItemsProperty = DependencyProperty.Register(
            "ChosenItems",
            typeof(ObservableCollection<Element>),
            typeof(MultiSelectListUserControl));

        public void NewButton_Pressed(object sender, RoutedEventArgs e)
        {
            if (!AllItems.Any() || AllItems.Count == ChosenItems.Count)
            {
                return;
            }

            var elem = AllItems.First(x => ChosenItems.All(y => x.ID != y.ID));
            ChosenItems.Add(elem);
        }

        public MultiSelectListUserControl()
        {
            InitializeComponent();
            SetValue(AllItemsProperty, new ObservableCollection<Element>());
            SetValue(ChosenItemsProperty, new ObservableCollection<Element>());
        }

        private void ComboBox_OnDropDownOpened(object sender, EventArgs e)
        {
            var c = (ComboBox)sender;
            c.Items.Filter = x => ChosenItems.All(y => ((Element)x).ID != y.ID) || ((Element)c.SelectedValue).ID == ((Element)x).ID;
        }
    }
}

这不仅不起作用，它也是一种实现我想要的非常复杂的方式。是否有更简单的方法来获得具有不同值的组合框列表？或者有人可以给我指针，以便我可以正确实现吗？

Answer 1

我终于通过@Ed Plunkett建议使用ComboBox es绑定的代理对象。这允许我在触发相关操作（如添加新列表项或在组合框中选择其他值）时刷新每个ComboBox的可用项，只需更换AvailableItems属性值即可每个ComboBoxBindingSource。

这也使得XAML更加清晰，因为每个ComboBox现在都具有适当的绑定：

<UserControl x:foobar x:Name="MultiSelectList">
    <Grid>
        <ListBox ItemsSource="{Binding ElementName=MultiSelectList, Path=ComboBoxBindingSources, Mode=TwoWay}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <ComboBox ItemsSource="{Binding Path=AvailableElements}" SelectedValue="{Binding Path=SelectedElement}" SelectionChanged="ComboBox_SelectionChanged" />
                </DataTemplate> 
            </ListBox.ItemTemplate>
        </ListBox>
        <Button Content="New" Click="NewButton_Pressed"/>
    </Grid>
</UserControl>

背后的工作代码是：

  using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Windows;
using System.Windows.Controls;

namespace WPFCentralOffice.UserControls
{
    public class Element : IEquatable<Element>
    {
        public int ID { get; set; }
        public string Caption { get; set; }

        public bool Equals(Element other)
        {
            return ID == other.ID;
        }

        public override string ToString()
        {
            return Caption;
        }
    }

    public class ComboBoxBindingSource : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public ComboBoxBindingSource(Element selectedElement, IEnumerable<Element> availableElements)
        {
            _selectedElement = selectedElement;
            AvailableElements = availableElements;
        }

        private Element _selectedElement;
        public Element SelectedElement
        {
            get { return _selectedElement; }
            set
            {
                _selectedElement = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("SelectedElement"));
                }
            }
        }

        private IEnumerable<Element> _availableElements;
        public IEnumerable<Element> AvailableElements
        {
            get { return _availableElements; }
            set
            {
                _availableElements = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("AvailableElements"));
                }
            }
        }
    }

    public partial class MultiSelectListUserControl : UserControl
    {
        public IEnumerable<Element> ChosenItems
        {
            get { return ComboBoxBindingSources.Select(x => x.SelectedElement); }
        }

        public ObservableCollection<Element> AllItems
        {
            get { return (ObservableCollection<Element>)GetValue(AllItemsProperty); }
            set { SetValue(AllItemsProperty, value); }
        }

        // ReSharper disable once InconsistentNaming
        public ObservableCollection<ComboBoxBindingSource> ComboBoxBindingSources
        {
            get { return (ObservableCollection<ComboBoxBindingSource>)GetValue(ComboBoxBindingSourcesProperty); }
            set { SetValue(ComboBoxBindingSourcesProperty, value); }
        }

        public static DependencyProperty AllItemsProperty = DependencyProperty.Register(
            "AllItems",
            typeof(ObservableCollection<Element>),
            typeof(MultiSelectListUserControl),
            new FrameworkPropertyMetadata(OnAllItemsChanged));

        private static void OnAllItemsChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ((MultiSelectListUserControl)d).RefreshAvailableItems();
        }

        public static DependencyProperty ComboBoxBindingSourcesProperty = DependencyProperty.Register(
            "ComboBoxBindingSources",
            typeof(ObservableCollection<ComboBoxBindingSource>),
            typeof(MultiSelectListUserControl));

        public void NewButton_Pressed(object sender, RoutedEventArgs e)
        {
            if (!AllItems.Any() || AllItems.Count == ComboBoxBindingSources.Count)
            {
                return;
            }

            var remainingItems = AllItems.Where(x => ChosenItems.All(y => x.ID != y.ID)).ToList();
            ComboBoxBindingSources.Add(new ComboBoxBindingSource(remainingItems.First(), remainingItems));
            RefreshAvailableItems();
        }

        public void ComboBox_SelectionChanged(object sender, RoutedEventArgs e)
        {
            RefreshAvailableItems();
        }

        private void RefreshAvailableItems()
        {
            if (ComboBoxBindingSources == null)
            {
                ComboBoxBindingSources = new ObservableCollection<ComboBoxBindingSource>();
            }
            foreach (var source in ComboBoxBindingSources)
            {
                var newAvailables =
                    AllItems.Where(
                        x => source.SelectedElement == x || ComboBoxBindingSources.All(y => y.SelectedElement != x));
                source.AvailableElements = newAvailables;
            }
        }

        public MultiSelectListUserControl()
        {
            InitializeComponent();
            SetValue(AllItemsProperty, new ObservableCollection<Element>());
        }
    }
}

过滤ListBox中的ComboBox

1 个答案: