如何绑定ListBoxItem的索引 [英] How can I bind against the Index of a ListBoxItem

问题描述

我想将列表框项目的z索引绑定到其索引。

I'd like to bind the z index of list box items to their index.

理想情况下，我们将有

<Style TargetType="{x:Type ListBoxItem}">
    <Setter Property="Panel.ZIndex"
            Value="{Binding RelativeSource={RelativeSource Self}, Path=-Index}" />
    <!-- ... -->

但是，列表框项目没有索引属性。

However, the list box item does not have an index property.

我可以想到一些疯狂的解决方案，但没有简单和优雅。

I can think of a number of crazy solutions but nothing simple and elegant.

任何人？

推荐答案

没有索引属性，但无论如何，-Index不会是有效的路径...您仍然需要一个转换器来否定该值。所以你可以做的是创建一个转换器，从 ItemContainerGenerator中获取索引

There is no Index property, but anyway "-Index" wouldn't be a valid path... you would still need a converter to negate the value. So what you can do is create a converter that retrieves the index from the ItemContainerGenerator

public class ItemContainerToZIndexConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var itemContainer = (DependencyObject)value;
        var itemsControl = FindAncestor<ItemsControl>(itemContainer);
        int index = itemsControl.ItemContainerGenerator.IndexFromContainer(itemContainer);
        return -index;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }

    public static T FindAncestor<T>(this DependencyObject obj) where T : DependencyObject
    {
        var tmp = VisualTreeHelper.GetParent(obj);
        while (tmp != null && !(tmp is T))
        {
            tmp = VisualTreeHelper.GetParent(tmp);
        }
        return (T)tmp;
    }
}


<Style TargetType="{x:Type ListBoxItem}">
    <Setter Property="Panel.ZIndex"
            Value="{Binding RelativeSource={RelativeSource Self}, Converter={StaticResource zIndexConverter}}" />
    <!-- ... -->

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