Question

在一些帮助下，我最近在自定义控件工作中创建了绑定集合。但是，令我惊讶的是，我被告知要使自定义控件属性更灵活（可以与其他参数化集合绑定），我需要使自定义控件的属性为IEnumerable<object>类型，因为协方差和逆转。但是，这似乎对我不起作用

这是控件的视图

<UserControl x:Class="BadaniaOperacyjne.Controls.Matrix"
            mc:Ignorable="d" Name="CustomMatrix"
            d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
            <!-- ... -->
        <Grid Grid.Row="2" Grid.Column="1" Name="contentGrid">
            <ListBox ItemsSource="{Binding ElementName=CustomMatrix, Path=ItemsList}">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding}"/>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
        </Grid>
    </Grid>
</UserControl>

它的代码隐藏在这里

#region ItemsList Property
public static readonly DependencyProperty ItemsListProperty =
    DependencyProperty.Register("ItemsList", typeof(IEnumerable<object>), typeof(Matrix), new PropertyMetadata(new PropertyChangedCallback(ItemsListChanged)));
public IEnumerable<object> ItemsList
{
    get { return GetValue(ItemsListProperty) as IEnumerable<object>; }
    set { SetValue(ItemsListProperty, value); }
}
private void ItemsListChanged(object value)
{
    System.Diagnostics.Debug.WriteLine("matrix: items list changed " + value);
    if (ItemsList != null)
    {
        //ItemsList.CollectionChanged += ItemsList_CollectionChanged;
        System.Diagnostics.Debug.WriteLine("got " + string.Join(",", ItemsList.ToList()));
    }
    else
    {
        System.Diagnostics.Debug.WriteLine("got null");
    }
}

void ItemsList_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
    System.Diagnostics.Debug.WriteLine("matrix: current items list collection changed");
}
private static void ItemsListChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    ((Matrix)d).ItemsListChanged(e.NewValue);
}
#endregion

以及使用该控件的Window是以下

<custom:Matrix x:Name="customMatrix" DockPanel.Dock="Top" Title="{Binding Title}" ItemsList="{Binding Items}"/>

与代码隐藏

public class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public ViewModel()
    {
        Items = new ObservableCollection<int> { 1, 2, 3, 4, 5, 6};

        Items.CollectionChanged += Items_CollectionChanged;
    }

    void Items_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        System.Diagnostics.Debug.WriteLine("problem manager: items list changed " + e.NewItems.Count);
    }

    public ObservableCollection<int> Items { get; private set; }

    protected string title;
    public string Title
    {
        get { return title; }
        set
        {
            if (title != value)
            {
                title = value;
                NotifyPropertyChanged("Title");
            }
        }
    }

    protected void NotifyPropertyChanged(string name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(name));
        }
    }
}

public ViewModel VM { get; private set; }

// the window's constructor
private ProblemManager()
{
    VM = new ViewModel();

    DataContext = VM;
    InitializeComponent();

    VM.Title = "title";
}

private int i = 0;
private void btnAddRow_Click(object sender, RoutedEventArgs e)
{
    //VM.Items.Add(++i);
    VM.Items[2] = 112;
    //customMatrix.ItemsList = new ObservableCollection<object> { 1, 2, 3 };
    //customMatrix.ItemsList.Add(66);
    //////
    VM.Title = (++i).ToString();
}

当我将DependencyProperty控件的ItemsList更改为ObservableCollection<int>或至少ObservableCollection<object>时，它可以正常工作。真的有可能吗？如果是这样，那么我犯的错误是什么？

Answer 1

Co-variance允许

IEnumerable但我只检查了allowed for reference types and not for value types (e.g. int)。

如果您从ObservableCollection<string>开始与string is reference type绑定，那么您的版本将有效。

所以你可以做的是使用IEnumerable (non-generic version)作为你的DP的返回类型，这样它也适用于值类型：

public static readonly DependencyProperty ItemsListProperty =
    DependencyProperty.Register("ItemsList", typeof(IEnumerable), typeof(Matrix),
        new PropertyMetadata(new PropertyChangedCallback(ItemsListChanged)));

public IEnumerable ItemsList
{
    get { return (IEnumerable)GetValue(ItemsListProperty); }
    set { SetValue(ItemsListProperty, value); }
}

将ObservableCollection <int>绑定到自定义控件的<IEnumerable <object> </object> </int>

1 个答案: