wpf - 绑定(bind)到相同数据源的互斥组合框 - MVVM 实现

Question

我不确定我的标题是否正确，但这就是我现在面临的问题..我有以下 XAML 代码..

        <ItemsControl.ItemTemplate>

        <DataTemplate>

            <StackPanel Orientation="Horizontal">

                        <ComboBox ItemsSource="{Binding Path=AvailableFields}"

                          SelectedItem="{Binding Path=SelectedField}"

                          ></ComboBox>

            </StackPanel>

        </DataTemplate>

        </ItemsControl.ItemTemplate>

这基本上做的是，如果我的数据源包含十个项目，这将生成 10 行组合框，并且所有组合框都绑定(bind)到相同的项目源。

现在我的要求是，一旦在第一个组合框中选择了某个项目，该项目就不应该在后续组合框中可用。在MVVM和WPF中如何满足这个需求？

Answer 1

事实证明，这比我开始编码时想象的要困难。下面的示例可以满足您的要求。组合框将包含仍然可用且未在另一个组合框中选择的所有字母。

XAML:

<Window x:Class="TestApp.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">

    <StackPanel>
        <ItemsControl ItemsSource="{Binding Path=SelectedLetters}">
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <ComboBox 
                        ItemsSource="{Binding Path=AvailableLetters}" 
                        SelectedItem="{Binding Path=Letter}" /> 
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </StackPanel>

</Window>

隐藏代码:

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

namespace TestApp
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            DataContext = new VM();
        }
    }

    public class VM : INotifyPropertyChanged
    {
        public VM()
        {
            SelectedLetters = new List<LetterItem>();
            for (int i = 0; i < 10; i++)
            {
                LetterItem letterItem = new LetterItem();
                letterItem.PropertyChanged += OnLetterItemPropertyChanged;
                SelectedLetters.Add(letterItem);
            }
        }

        public List<LetterItem> SelectedLetters { get; private set; }

        private void OnLetterItemPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName != "Letter")
            {
                return;
            }

            foreach (LetterItem letterItem in SelectedLetters)
            {
                letterItem.RefreshAvailableLetters(SelectedLetters);
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        public class LetterItem : INotifyPropertyChanged
        {
            static LetterItem()
            {
                _allLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".Select(c => c.ToString());
            }

            public LetterItem()
            {
                AvailableLetters = _allLetters;
            }

            public void RefreshAvailableLetters(IEnumerable<LetterItem> letterItems)
            {
                AvailableLetters = _allLetters.Where(c => !letterItems.Any(li => li.Letter == c) || c == Letter);
            }

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


            private string _letter;
            public string Letter
            {
                get { return _letter; }
                set
                {
                    if (_letter == value)
                    {
                        return;
                    }
                    _letter = value;
                    if (PropertyChanged != null)
                    {
                        PropertyChanged(this, new PropertyChangedEventArgs("Letter"));
                    }
                }
            }

            public event PropertyChangedEventHandler PropertyChanged;

            private static readonly IEnumerable<string> _allLetters;
        }
    }
}