将 Grid 用作 ItemsPanelTemplate 的 ListBox 会产生奇怪的绑定错误 [英] ListBox with Grid as ItemsPanelTemplate produces weird binding errors

问题描述

我有一个 ListBox 控件，并且在网格布局中呈现固定数量的 ListBoxItem 对象.所以我将我的 ItemsPanelTemplate 设置为 Grid.

I've got a ListBox control and I'm presenting a fixed number of ListBoxItem objects in a grid layout. So I've set my ItemsPanelTemplate to be a Grid.

我正在从后面的代码访问 Grid 以配置 RowDefinitions 和 ColumnDefinitions.

I'm accessing the Grid from code behind to configure the RowDefinitions and ColumnDefinitions.

到目前为止，一切都按我的预期工作.我有一些自定义的 IValueConverter 实现，用于返回每个 ListBoxItem 应该出现的 Grid.Row 和 Grid.Column.

So far it's all working as I expect. I've got some custom IValueConverter implementations for returning the Grid.Row and Grid.Column that each ListBoxItem should appear in.

但是我有时会遇到奇怪的绑定错误，我无法弄清楚它们发生的确切原因，或者即使它们在我的代码中.

However I get weird binding errors sometimes, and I can't figure out exactly why they're happening, or even if they're in my code.

这是我得到的错误:

System.Windows.Data 错误:4:找不到与引用RelativeSource FindAncestor，AncestorType='System.Windows.Controls.ItemsControl'，AncestorLevel='1'' 绑定的源.BindingExpression:Path=Horizo​​ntalContentAlignment;数据项=空；目标元素是'ListBoxItem'(名称='')；目标属性是Horizo​​ntalContentAlignment"(类型Horizo​​ntalAlignment")

谁能解释一下是怎么回事?

Can anybody explain what's going on?

哦，还有，这是我的 XAML:

Oh, and, here's my XAML:

<UserControl.Resources>
    <!-- Value Converters -->
    <v:GridRowConverter x:Key="GridRowConverter" />
    <v:GridColumnConverter x:Key="GridColumnConverter" />
    <v:DevicePositionConverter x:Key="DevicePositionConverter" />
    <v:DeviceBackgroundConverter x:Key="DeviceBackgroundConverter" />

    <Style x:Key="DeviceContainerStyle" TargetType="{x:Type ListBoxItem}">
        <Setter Property="FocusVisualStyle" Value="{x:Null}" />
        <Setter Property="Background" Value="Transparent" />

        <Setter Property="Grid.Row" Value="{Binding Path=DeviceId, Converter={StaticResource GridRowConverter}}" />
        <Setter Property="Grid.Column" Value="{Binding Path=DeviceId, Converter={StaticResource GridColumnConverter}}" />

        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ListBoxItem}">
                    <Border CornerRadius="2" BorderThickness="1" BorderBrush="White" Margin="2" Name="Bd"
                            Background="{Binding Converter={StaticResource DeviceBackgroundConverter}}">
                        <TextBlock FontSize="12" HorizontalAlignment="Center" VerticalAlignment="Center" 
                                Text="{Binding Path=DeviceId, Converter={StaticResource DevicePositionConverter}}" >
                            <TextBlock.LayoutTransform>
                                <RotateTransform Angle="270" />
                            </TextBlock.LayoutTransform>
                        </TextBlock>
                    </Border>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsSelected" Value="true">
                            <Setter TargetName="Bd" Property="BorderThickness" Value="2" />
                            <Setter TargetName="Bd" Property="Margin" Value="1" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>            
    </Style>        
</UserControl.Resources>

<Border CornerRadius="3" BorderThickness="3" Background="#FF333333" BorderBrush="#FF333333" >
    <Grid ShowGridLines="False">
        <Grid.RowDefinitions>
            <RowDefinition Height="15" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <StackPanel Grid.Row="0" Orientation="Horizontal">
            <Image Margin="20,3,3,3" Source="Barcode.GIF" Width="60" Stretch="Fill" />
        </StackPanel>

        <ListBox ItemsSource="{Binding}" x:Name="lstDevices" Grid.Row="1" 
                 ItemContainerStyle="{StaticResource DeviceContainerStyle}"
                 Background="#FF333333"
                 SelectedItem="{Binding SelectedDeviceResult, ElementName=root, Mode=TwoWay}" >
            <ListBox.ItemsPanel>
                <ItemsPanelTemplate>
                    <Grid>
                        <Grid.LayoutTransform>
                            <RotateTransform Angle="90" />
                        </Grid.LayoutTransform>                            
                    </Grid>
                </ItemsPanelTemplate>
            </ListBox.ItemsPanel>
        </ListBox>
    </Grid>
</Border>

推荐答案

绑定问题来自于ListBoxItem的默认样式.默认情况下，当将样式应用于元素时，WPF 会查找默认样式并应用默认样式中未在自定义样式中专门设置的每个属性.请参阅 Ian Griffiths 撰写的 这篇很棒的博文有关此行为的详细信息.

The binding problem comes from the default style for ListBoxItem. By default when applying styles to elements WPF looks for the default styles and applies each property that is not specifically set in the custom style from the default style. Refer to this great blog post By Ian Griffiths for more details on this behavior.

回到我们的问题.这是 ListBoxItem 的默认样式:

Back to our problem. Here is the default style for ListBoxItem:

<Style
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:s="clr-namespace:System;assembly=mscorlib"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    TargetType="{x:Type ListBoxItem}">
    <Style.Resources>
       <ResourceDictionary/>
    </Style.Resources>
    <Setter Property="Panel.Background">
       <Setter.Value>
          <SolidColorBrush>
        #00FFFFFF
          </SolidColorBrush>
       </Setter.Value>
    </Setter>
    <Setter Property="Control.HorizontalContentAlignment">
       <Setter.Value>
          <Binding Path="HorizontalContentAlignment" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=ItemsControl, AncestorLevel=1}"/>
       </Setter.Value>
    </Setter>
    <Setter Property="Control.VerticalContentAlignment">
       <Setter.Value>
          <Binding Path="VerticalContentAlignment" RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=ItemsControl, AncestorLevel=1}"/>
       </Setter.Value>
    </Setter>
    <Setter Property="Control.Padding">
       <Setter.Value>
          <Thickness>
        2,0,0,0
          </Thickness>
       </Setter.Value>
    </Setter>
    <Setter Property="Control.Template">
       <Setter.Value>
          <ControlTemplate TargetType="{x:Type ListBoxItem}">
             ...
          </ControlTemplate>
       </Setter.Value>
    </Setter>
 </Style>

请注意，我已删除 ControlTemplate 以使其紧凑(我已使用 StyleSnooper -检索样式).您可以看到有一个绑定，其相对源设置为带有 ItemsControl 类型的祖先.因此，在您的情况下，绑定时创建的 ListBoxItems 没有找到它们的 ItemsControl.您能否提供更多关于 ListBox 的 ItemsSource 的信息?

Note that I have removed the ControlTemplate to make it compact (I have used StyleSnooper - to retrieve the style). You can see that there is a binding with a relative source set to ancestor with type ItemsControl. So in your case the ListBoxItems that are created when binding did not find their ItemsControl. Can you provide more info with what is the ItemsSource for your ListBox?

P.S.:消除错误的一种方法是在您的自定义样式中为 Horizo​​ntalContentAlignment 和 VerticalContentAlignment 创建新的设置器.

P.S.: One way to remove the errors is to create new setters for HorizontalContentAlignment and VerticalContentAlignment in your custom Style.

这篇关于将 Grid 用作 ItemsPanelTemplate 的 ListBox 会产生奇怪的绑定错误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！