如何根据列表中是否存在绑定对象来设置 CheckBox.IsChecked

Question

有 2 个列表——AvailableItems 和 SelectedItems。

AvailableItems 显示在一个 ListBox 中，每个 ListBoxItem 都包含一个 CheckBox。目的是如果绑定项位于 SelectedItems 中，则检查 CheckBox。

我可以在不处理代码隐藏中的 Checked 和 Unchecked 且不向项目类添加 IsSelected 属性的情况下实现此目的吗？

这是到目前为止的 XAML：

   <ListBox Name="ListBox1" ItemsSource="{Binding Path=AvailableItems}">
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <StackPanel></StackPanel>
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <DockPanel>
                    <CheckBox Name="cb1"></CheckBox>
                    <TextBlock Text="{Binding}"></TextBlock>
                </DockPanel>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ListBox>

和隐藏代码：

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            _availableItems.Add(Colors.Red);
            _availableItems.Add(Colors.Green);
            _availableItems.Add(Colors.Blue);

            _selectedItems.Add(Colors.Green);

            this.DataContext = this;
        }

        ObservableCollection<Color> _selectedItems = new ObservableCollection<Color>();
        public ObservableCollection<Color> SelectedItems
        {
            get { return _selectedItems; }
            set { _selectedItems = value; }
        }

        ObservableCollection<Color> _availableItems = new ObservableCollection<Color>();
        public ObservableCollection<Color> AvailableItems
        {
            get { return _availableItems; }
            set { _availableItems = value; }
        }
    }

可以将上面的 xaml/代码直接复制到新的 WPF 项目中进行测试。

Answer 1

您定义一个多值转换器，它接受一个项目和一个集合并返回一个布尔值：

public class CollectionContainsConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var item = values[0];
        var collection = values[1] as IList;
        return collection.Contains(item);
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

然后像这样使用它：

    <ListBox Name="ListBox1" ItemsSource="{Binding Path=AvailableItems}">
        <ListBox.Resources>
            <local:CollectionContainsConverter x:Key="contains"/>
        </ListBox.Resources>
        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <StackPanel></StackPanel>
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <DockPanel>
                    <CheckBox Name="cb1">
                        <CheckBox.IsChecked>
                            <MultiBinding Converter="{StaticResource contains}" Mode="OneWay">
                                <Binding Mode="OneWay"/>
                                <Binding ElementName="ListBox1" Path="DataContext.SelectedItems" Mode="OneWay"/>
                            </MultiBinding>
                        </CheckBox.IsChecked>
                    </CheckBox>
                    <TextBlock Text="{Binding}"></TextBlock>
                </DockPanel>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ListBox>

处理反向转换留作练习。

Answer 2

使用 MVVM 进行粗略模型

创建一个类来表示每个项目所需的所有数据，例如 Checked 和描述

class CustomItem : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private bool _isSelected;
        private string _customColour;

        public bool IsSelected
        {
            get { return _isSelected; }
            set 
            { 
                _isSelected = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged.Invoke(this, new PropertyChangedEventArgs("IsSelected"));
                }
            }
        }

        public string CustomColour
        {
            get { return _customColour; }
            set
            {
                _customColour = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged.Invoke(this, new PropertyChangedEventArgs("CustomColour"));
                }
            }
        }        
    }

创建一个类来表示您想要显示的项目集合

   class CustomItems : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private ObservableCollection<CustomItem> _listOfCustomItems;

        public CustomItems()
        {
            ListOfCustomItems = new ObservableCollection<CustomItem>();

            var c = new CustomItem
                        {
                            IsSelected = false, 
                            CustomColour = "Red"
                        };
            ListOfCustomItems.Add(c); 

            c = new CustomItem
                    {
                        IsSelected = true, 
                        CustomColour = "Green"
                    };
            ListOfCustomItems.Add(c);

            c = new CustomItem
                    {
                        IsSelected = false, 
                        CustomColour = "Blue"
                    };

            ListOfCustomItems.Add(c);
        }

        public ObservableCollection<CustomItem> ListOfCustomItems
        {
            get { return _listOfCustomItems; }
            set 
            { 
                _listOfCustomItems = value;
                if (PropertyChanged != null)
                {
                    PropertyChanged.Invoke(this, new PropertyChangedEventArgs("ListOfCustomItems"));
                }
            }
        }

        public List<CustomItem> SelectedItems
        {
            get
            {
                return (from customItem in ListOfCustomItems 
                        where customItem.IsSelected 
                        select customItem).ToList();
            }
        }
    }

添加到窗口

 <Window.Resources>
        <WpfApplication1:CustomItems x:Key="CI"/>
    </Window.Resources>
    <Grid DataContext="{StaticResource CI}">
        <ListBox ItemsSource="{Binding Path=ListOfCustomItems}">
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <StackPanel></StackPanel>
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <DockPanel>
                        <CheckBox IsChecked="{Binding Path=IsSelected}"/>
                        <TextBlock Text="{Binding Path=CustomColour}"/>
                    </DockPanel>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ListBox>
    </Grid>

您维护一个项目列表，并提供一个属性获取执行简单 LINQ 选择的选定内容。简单的。根据需要更改数据类型。