Question

从此示例：

https://blog.verslu.is/stackoverflow-answers/alternate-row-color-listview/

如何使用分组列表视图实现它？我想在列表视图的每个组中都有备用行颜色，我已经尝试用分组的列表视图实现它，但是总是给我“ System.InvalidCastException：指定的转换无效”。在DataTemplateSelector中。

列表视图代码：

 <DataTemplate x:Key="evenTemplate">
            <ViewCell>
                <customRenders:GridConf  Margin="0,0,0,0" HorizontalOptions="FillAndExpand"  ColumnSpacing="0" RowSpacing="0" ConfigurationItem ="{Binding .}">
                    <customRenders:GridConf.ColumnDefinitions>
                        <ColumnDefinition Width="80"/>
                        <ColumnDefinition Width="*"/>
                    </customRenders:GridConf.ColumnDefinitions>
                    <customRenders:GridConf.RowDefinitions>
                        <RowDefinition Height="*"/>
                    </customRenders:GridConf.RowDefinitions>
                    <BoxView VerticalOptions="CenterAndExpand" HeightRequest="50" Grid.ColumnSpan="1" Margin="-30,0,0,0" Grid.Column="1" HorizontalOptions="FillAndExpand"  BackgroundColor="LightGray"/>
                    <Label VerticalOptions="CenterAndExpand" Margin="10,0,0,0" Grid.Column="1" VerticalTextAlignment="Center" HorizontalOptions="StartAndExpand"  Text="tetetetetetet"></Label>
                    <Image Grid.Column="1" Source="HidePass.png" HeightRequest="30" VerticalOptions="CenterAndExpand" HorizontalOptions="End">
                        <Image.GestureRecognizers>
                            <TapGestureRecognizer NumberOfTapsRequired="1" ></TapGestureRecognizer>
                        </Image.GestureRecognizers>
                    </Image>
                    <customRenders:CachedImageItem Grid.Column="0" ConfigurationItem ="{Binding .}" HorizontalOptions="Start" HeightRequest="80" VerticalOptions="Center" x:Name="Image2" Source="{Binding Img}"/>
                    <customRenders:GridConf.GestureRecognizers>
                        <TapGestureRecognizer NumberOfTapsRequired="1" ></TapGestureRecognizer>
                    </customRenders:GridConf.GestureRecognizers>
                </customRenders:GridConf>
            </ViewCell>
        </DataTemplate>
        <DataTemplate x:Key="unevenTemplate">
            <ViewCell>
                <customRenders:GridConf  Margin="20,0,0,0" HorizontalOptions="FillAndExpand"  ColumnSpacing="0" RowSpacing="0" ConfigurationItem ="{Binding .}">
                    <customRenders:GridConf.ColumnDefinitions>
                        <ColumnDefinition Width="80"/>
                        <ColumnDefinition Width="*"/>
                    </customRenders:GridConf.ColumnDefinitions>
                    <customRenders:GridConf.RowDefinitions>
                        <RowDefinition Height="*"/>
                    </customRenders:GridConf.RowDefinitions>
                    <BoxView VerticalOptions="CenterAndExpand" HeightRequest="50" Grid.ColumnSpan="1" Margin="-30,0,0,0" Grid.Column="1" HorizontalOptions="FillAndExpand"  BackgroundColor="LightGray"/>
                    <Label VerticalOptions="CenterAndExpand" Margin="10,0,0,0" Grid.Column="1" VerticalTextAlignment="Center" HorizontalOptions="StartAndExpand"  Text="teteteteteette"></Label>
                    <Image Grid.Column="1" Source="HidePass.png" HeightRequest="30" VerticalOptions="CenterAndExpand" HorizontalOptions="End">
                        <Image.GestureRecognizers>
                            <TapGestureRecognizer NumberOfTapsRequired="1" ></TapGestureRecognizer>
                        </Image.GestureRecognizers>
                    </Image>
                    <customRenders:CachedImageItem Grid.Column="0" ConfigurationItem ="{Binding .}" HorizontalOptions="Start" HeightRequest="80" VerticalOptions="Center" x:Name="Image2" Source="{Binding Img}"/>
                    <customRenders:GridConf.GestureRecognizers>
                        <TapGestureRecognizer NumberOfTapsRequired="1" ></TapGestureRecognizer>
                    </customRenders:GridConf.GestureRecognizers>
                </customRenders:GridConf>
            </ViewCell>
        </DataTemplate>
        <customRenders1:AlternateColorDataTemplateSelector2 x:Key="alternateColorDataTemplateSelector"
                                                  EvenTemplate="{StaticResource evenTemplate}"
                                                  UnevenTemplate="{StaticResource unevenTemplate}" />
    </ResourceDictionary>
</ContentPage.Resources>
<ListView x:Name="lst" IsGroupingEnabled="True"  ItemTemplate="{StaticResource alternateColorDataTemplateSelector}" ItemsSource="{Binding Item}" Margin="5,5,0,0" HasUnevenRows="True" SeparatorVisibility="None">
    <ListView.GroupHeaderTemplate>
        <DataTemplate>
            <customRenders:NativeCell>
                <customRenders:NativeCell.View>
                    <ContentView Padding="10,0,0,0">
                        <StackLayout>
                            <Label Text="{Binding Key.Category}" VerticalOptions="Center"/>
                        </StackLayout>
                        <ContentView.GestureRecognizers>
                            <TapGestureRecognizer Command="{Binding Source={x:Reference ProtocolosPage}, Path=BindingContext.HeaderSelectedCommand}" CommandParameter="{Binding .}"/>
                        </ContentView.GestureRecognizers>
                    </ContentView>
                </customRenders:NativeCell.View>
            </customRenders:NativeCell>
        </DataTemplate>
    </ListView.GroupHeaderTemplate>
</ListView>

AlternateColorDataTemplateSelector：

public DataTemplate EvenTemplate { get; set; }
public DataTemplate UnevenTemplate { get; set; }

protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
{
    // TODO: Maybe some more error handling here
    return ((List<Product>)((ListView)container).ItemsSource).IndexOf(item as Product) % 2 == 0 ? EvenTemplate : UnevenTemplate;
}

ViewModel

public class ProductsViewModel: BindableBase
{
    public class SelectCategoryViewModel
    {
        public string Category { get; set; }
        public bool Selected { get; set; }
    }


    private ObservableCollection<Grouping<string, Product>> _ProductsGrouped;

    public ObservableCollection<Product> Productitems { get; set; }

    public ObservableCollection<Grouping<string, Models.Product>> ProductsGrouped
    {
        get
        {
            return _ProductsGrouped;

        }
        set
        {
            _ProductsGrouped = value;
            OnPropertyChanged();

        }
    }


    public ObservableCollection<Grouping<SelectCategoryViewModel, Product>> Item { get; set; }

    public DelegateCommand<Grouping<SelectCategoryViewModel, Product>> HeaderSelectedCommand
    {
        get
        {
            return new DelegateCommand<Grouping<SelectCategoryViewModel, Product>>(g =>
            {
                if (g == null) return;
                g.Key.Selected = !g.Key.Selected;
                if (g.Key.Selected)
                {
                    Productitems.Where(i => (i.Category.Equals(g.Key.Category)))
                        .ForEach(g.Add);
                }
                else
                {
                    g.Clear();
                }
            });
        }
    }

    public ProductsViewModel()
    {
        Productitems = new ObservableCollection<Product>
        {
            new Product
            {
                Img = "dss.png",
                Url = "Teste",
                Category = "service",
                Title = "sdsadsadsdsdsa"
            },
            new Product
            {
                Img = "dss.png",
                Url = "Teste3",
                Category = "service",
                Title = "sdsadsadsdsdsatest2"
            },
            new Product
            {
                Img = "dss.png",
                Url = "Teste2",
                Category = "Farmacy",
                Title = "sdsadsadsdsdsaes"
            },
            new Product
            {
                Img = "dss.png",
                Url = "Teste4",
                Category = "Farmacy",
                Title = "sdsadsadsdsdsaF"
            },
            new Product
            {
                Img = "dss.png",
                Url = "Teste7",
                Category = "Farmacy",
                Title = "sdsadsadsdsdsaFarmarcia2"
            },
            new Product
            {
                Img = "dss.png",
                Url = "Teste9",
                Category = "Farmacy",
                Title = "sdsadsadsdsdsae"
            }
        };

        Item = new ObservableCollection<Grouping<SelectCategoryViewModel, Product>>();
        var selectCategories =
            Productitems.Select(x => new SelectCategoryViewModel { Category = x.Category, Selected = false })
                .GroupBy(sc => new { sc.Category })
                .Select(g => g.First())
                .ToList();
        selectCategories.ForEach(sc => Item.Add(new Grouping<SelectCategoryViewModel, Product>(sc, new List<Product>())));
    }
}

Answer 1

这不起作用，因为AlternateColorDataTemplateSelector中的代码将ItemSource强制转换为List。使用分组时，它不能是简单的列表。

另一方面，当您对一个组执行IndexOf时，您将收到该组中的索引，该索引不需要与完整列表中的索引相对应。

在此处找到示例存储库：https://github.com/jfversluis/GroupedListViewAlternateRowColor。

在改编的DataTemplateSelector中，我将整个列表弄平，然后从那里获取索引。这是代码：

public class AlternateColorDataTemplateSelector : DataTemplateSelector
{
    public DataTemplate EvenTemplate { get; set; }
    public DataTemplate UnevenTemplate { get; set; }

    private List<string> flatList;

    protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
    {
        if (flatList == null)
        {
            var groupedList = (ObservableCollection<Grouping<string, string>>)((ListView)container).ItemsSource;
            flatList = groupedList.SelectMany(group => group).ToList();
        }

        return flatList.IndexOf(item as string) % 2 == 0 ? EvenTemplate : UnevenTemplate;
    }
}

作为一种优化，我只创建了平面列表一次。每当列表使用新项目更新时，这可能会出错。我没有测试。

结果如下：

备用行颜色GroupedListview

1 个答案: