根据ListBoxItem在ListBox中的索引来设置其样式 [英] Styling a ListBoxItem depending on its index in the ListBox

问题描述

如果SomeProperty的值为10，我想更改ListBox中第一项的边距，而没有代码隐藏. 这是我到目前为止的内容:

I want to change the margin of the first item in the ListBox if SomeProperty value is 10, without code-behind. This is what I have so far:

<ListBox  x:Class="Windows.CustomList"
                 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
                 xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
                 xmlns:local="clr-namespace:Windows"
                 mc:Ignorable="d" x:Name="MyList"
                 d:DesignHeight="300" d:DesignWidth="300">
    <ListBox.ItemContainerStyle>
        <Style TargetType="{x:Type ListBoxItem}">
            <Style.Triggers>
                <MultiDataTrigger>
                    <MultiDataTrigger.Conditions>
                        <Condition Binding="{Binding Path=SomeProperty}" Value="10"/>
                        <Condition Binding="{Binding Path=Items.Count, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type ListBox}}}" Value="1" />
                    </MultiDataTrigger.Conditions>
                    <Setter Property="Margin">
                        <Setter.Value>
                            <Thickness Left="500"/>
                        </Setter.Value>
                    </Setter>
                </MultiDataTrigger>
            </Style.Triggers>
        </Style>
    </ListBox.ItemContainerStyle>
    <ListBox.ItemTemplate>
        <DataTemplate>
            <local:ListBoxItemCustomTemplate/>
        </DataTemplate>
    </ListBox.ItemTemplate>
    <ListBox.ItemsPanel>
        <ItemsPanelTemplate>
            <WrapPanel Orientation="Horizontal"/>
        </ItemsPanelTemplate>
    </ListBox.ItemsPanel>
</ListBox>

当我尝试这种方法时，我得到:

When I try this approach I get:

System.Windows.Data错误:4:找不到参考'RelativeSource FindAncestor，AncestorType ='ListBox'，AncestorLevel ='1''的绑定源. BindingExpression:Path = Items.Count; DataItem = null;目标元素是'ListBox'(Name =''); target属性为"NoTarget"(类型为"Object")

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='ListBox', AncestorLevel='1''. BindingExpression:Path=Items.Count; DataItem=null; target element is 'ListBox' (Name=''); target property is 'NoTarget' (type 'Object')

如果我只有第一个条件，它将正确应用边距. 我尝试过的另一种方法是使用ElementName:

If I have only the first condition, it applies the margin properly. Another way I tried was by using the ElementName:

这种方法不会产生任何错误，但也不起作用.

This approach doesn't give any error but it's not working either.

任何帮助将不胜感激.

推荐答案

请参见

See AlternationIndex. (You can use a very high AlternationCount to ensure that only the first item has index 0 and trigger on that).

这有点滥用，更干净的方法是值转换器/多值转换器，它通过listBox.Items.IndexOf(currentItem)之类的方法获取索引.

This is a bit abusive, a cleaner method would be a value converter / multi value converter, that gets the index via something like listBox.Items.IndexOf(currentItem).

这篇关于根据ListBoxItem在ListBox中的索引来设置其样式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！