Question

最终目标是能够在列表框的第一个和最后一个元素上设置特定的ItemContainerStyle;

到目前为止，转换器是：

public class IsFirstItemConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        bool result = false;
        result = ((IList<object>)parameter).First() == value;

        return result;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}
public class IsLastItemConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        bool result = false;
        result = ((IList<object>)parameter).Last() == value;

        return result;
    }

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

并实施：

<DataTrigger Value="True" Binding="{Binding Converter={StaticResource IsFirstItemConverter},ConverterParameter=Items,  ElementName=SubItems}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ListBoxItem}">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="First"/>
                    <ContentPresenter/>
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</DataTrigger>

错误是：

InvalidCastException：无法将类型为“System.String”的对象强制转换为输入'System.Collections.Generic.IList`1 [System.Object]'。

我确定我在多个位置搞砸了，只是没有足够的XAML和绑定来缩小其中的位置。

Answer 1

以下改编自问题的评论工作完美：

public class IsLastItemConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        DependencyObject item = (DependencyObject)value;
        ItemsControl ic = ItemsControl.ItemsControlFromItemContainer(item);

        return ic.ItemContainerGenerator.IndexFromContainer(item) == ic.Items.Count - 1;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

public class IsFirstItemConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        DependencyObject item = (DependencyObject)value;
        ItemsControl ic = ItemsControl.ItemsControlFromItemContainer(item);

        return ic.ItemContainerGenerator.IndexFromContainer(item) == 0;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

public class IsOnlyItemConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        DependencyObject item = (DependencyObject)value;
        ItemsControl ic = ItemsControl.ItemsControlFromItemContainer(item);

        return (ic.ItemContainerGenerator.IndexFromContainer(item) == 0 && ic.ItemContainerGenerator.Items.Count == 1);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

实现：

<DataTrigger Binding="{Binding RelativeSource={RelativeSource Self}, Converter={StaticResource IsLastItemConverter}}" Value="True">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ListBoxItem}">
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="└"/>
                    <ContentPresenter/>
                </StackPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</DataTrigger>

神奇似乎是ItemsControlFromItemContainer使它成为所以我不必将项及其集合实例都传递给转换器，而只是项目和转换器可以推断父集合。

尝试为对象集合绑定创建IsFirstItem和IsLastItem IValueConverter

1 个答案: