WPF ItemsControl 第一项始终未加载/显示

Question

我的 ItemsControl 有一个奇怪的问题。它并不总是显示第一项。我不确定，但我怀疑这可能与使用 ICollectionView 有关？

我怀疑是因为根据 SortDirection，它总是隐藏第一项。

例如，如果我有 a,b,c,d,e,f,g 和 ASCENDING，我得到 b,c,d,e,f,g。如果 DESCENDING，我得到 f,e,d,c,b,a。

我正在绑定我的代码：

private ICollectionView _collectionView;
    public ICollectionView IngredientsOrModifiers
    {
        get
        {
            _collectionView = _collectionView ?? CollectionViewSource.GetDefaultView(_ingredientsOrModifiers);
            if (!_collectionView.SortDescriptions.Any())
            {
                _collectionView.SortDescriptions.Add(new SortDescription(nameof(CheckIngredientOrModifierViewModel.LowercaseCheckTitle), ListSortDirection.Ascending));
            }

            if (!_collectionView.GroupDescriptions.Any())
            {
                _collectionView.GroupDescriptions.Add(new PropertyGroupDescription(null, IngredientGroupConverter.Default));
            }

            return _collectionView;
        }
    }

我的 ItemsControl 是：

<ItemsControl Grid.Row="2"
                      Grid.ColumnSpan="3"
                      Margin="5,0,0,0"
                      ItemsSource="{Binding IngredientsOrModifiers.Groups}">
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Button x:Name="subitemButton" 
                            BorderThickness="0"
                            FocusVisualStyle="{x:Null}"
                            Margin="0,2"
                            HorizontalContentAlignment="Stretch"
                            Background="Transparent"
                            Command="{Binding Path=Items[0].CheckIfShouldShowComplimentaryItemDialogCommand}"
                            CommandParameter="{Binding Path=Items[0]}">
                        <Button.Style>
                            <Style TargetType="Button">
                                <Setter Property="Background"
                                        Value="Transparent" />
                                <Setter Property="Template">
                                    <Setter.Value>
                                        <ControlTemplate TargetType="Button">
                                            <Grid Background="{TemplateBinding Background}">
                                                <ContentPresenter />
                                            </Grid>
                                        </ControlTemplate>
                                    </Setter.Value>
                                </Setter>
                            </Style>
                        </Button.Style>
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="*" />
                                <ColumnDefinition Width="43" />
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="*" />
                                <RowDefinition Height="Auto" />
                            </Grid.RowDefinitions>
                            <TextBlock Text="{Binding Items[0].LowercaseCheckTitle}"
                                       Style="{StaticResource CartSubItemTitleStyle}"
                                       FontFamily="{Binding Path=Items[0].IsComplimentary, Converter={x:Static converters2:BooleanToFontFamilyConverter.Default}}"
                                       FontWeight="{Binding Path=Items[0].IsComplimentary, Converter={x:Static converters2:BooleanToFontWeightConverter.Default}}"
                                       x:Name="titleField" />
                            <Button Grid.Column="1"
                                    x:Name="removeButton"
                                    Style="{StaticResource RemoveSubItemButtonStyle}"
                                    Command="{Binding RemoveIngredientOrModifierCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type UserControl}}}"
                                    CommandParameter="{Binding Items[0]}"
                                    Visibility="Collapsed" />
                            <ItemsControl Grid.Row="1"
                                          Grid.ColumnSpan="2"
                                          Margin="5,0,0,0"
                                          ItemsSource="{Binding Items[0].ItemModifiers}">
                                <ItemsControl.ItemTemplate>
                                    <DataTemplate>
                                        <Grid Margin="0,2">
                                            <Grid.ColumnDefinitions>
                                                <ColumnDefinition Width="*" />
                                                <ColumnDefinition Width="43" />
                                            </Grid.ColumnDefinitions>
                                            <TextBlock Text="{Binding Title, Converter={x:Static converters:StringCaseConverter.ToLower}}"
                                                       Style="{StaticResource CartSubItemTitleStyle}" />
                                        </Grid>
                                    </DataTemplate>
                                </ItemsControl.ItemTemplate>
                            </ItemsControl>
                        </Grid>
                    </Button>
                    <DataTemplate.Triggers>
                        <DataTrigger Binding="{Binding Path=IsCheckOut, RelativeSource={RelativeSource AncestorType={x:Type controls:ShoppingCartControl}}}"
                                     Value="False">
                            <DataTrigger.Setters>
                                <Setter Property="MinHeight"
                                        TargetName="subitemButton"
                                        Value="44" />
                            </DataTrigger.Setters>
                        </DataTrigger>
                        <DataTrigger Binding="{Binding ItemCount, Converter={x:Static converters:CountToBooleanConverter.Default}, ConverterParameter=1}" Value="True">
                            <DataTrigger.Setters>
                                <Setter Property="Text" TargetName="titleField">
                                    <Setter.Value>
                                        <MultiBinding Converter="{x:Static converters2:StringFormatMultiConverter.Default}" ConverterParameter="{}{0} ({1})" UpdateSourceTrigger="PropertyChanged">
                                            <Binding Path="Items[0].LowercaseCheckTitle" />
                                            <Binding Path="ItemCount" />
                                        </MultiBinding>
                                    </Setter.Value>
                                </Setter>
                            </DataTrigger.Setters>
                        </DataTrigger>
                        <MultiDataTrigger>
                            <MultiDataTrigger.Conditions>
                                <Condition Binding="{Binding Path=CanRemoveItems, RelativeSource={RelativeSource AncestorType={x:Type controls:ShoppingCartControl}}}" Value="True" />
                                <Condition Binding="{Binding Path=IsCheckOut, RelativeSource={RelativeSource AncestorType={x:Type controls:ShoppingCartControl}}}" Value="False" />
                                <Condition Binding="{Binding Path=Items[0].CanRemove}" Value="True" />
                            </MultiDataTrigger.Conditions>
                            <MultiDataTrigger.Setters>
                                <Setter TargetName="removeButton" Property="Visibility" Value="Visible" />
                            </MultiDataTrigger.Setters>
                        </MultiDataTrigger>
                    </DataTemplate.Triggers>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>

编辑：

这是转换器：

public class IngredientGroupConverter : IValueConverter
{
    public static IngredientGroupConverter Default = new IngredientGroupConverter();

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        CheckIngredientOrModifierViewModel vm = value as CheckIngredientOrModifierViewModel;

        if (vm != null)
        {
            if (vm.ItemModifiers.Any())
            {
                StringBuilder builder = new StringBuilder(vm.LowercaseCheckTitle);

                foreach (var mod in vm.ItemModifiers)
                {
                    builder.Append("|");
                    builder.Append(mod.Title);
                }

                return builder.ToString();
            }
            else
            {
                return vm.LowercaseCheckTitle;
            }
        }

        return null;
    }

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

Answer 1

我发现了问题所在。这是一个布局问题；我在 ItemsControl 中添加了 Top-Margin 40，它显示了缺少的第一项。