如何在AthleteModel的x:DataTemplate中绑定外部Sports.IsExpanded至IsVisible

我希望将SportsModel类型中的Sports.IsExpanded属性绑定到controls:TappableStack的IsVisible属性，但该控件所在的x:DataTemplate已设置x:DataType为AthleteModel，请问如何访问当前x:DataTemplate数据类型之外的变量？

相关XAML代码示例：

<CollectionView IsGrouped="true" 
                ItemsSource="{x:Binding AthletesPerSportsList}"
                Margin="0,-15,0,0">
    <CollectionView.GroupHeaderTemplate>
        <DataTemplate x:DataType="model:SportsModel">
            <StackLayout BackgroundColor="{x:StaticResource PurpleLight}">
                <StackLayout.GestureRecognizers>
                    <TapGestureRecognizer Command="{x:Binding Source={x:Reference Athletes}, 
                                      Path=BindingContext.SportTappedCommand}" 
                                      CommandParameter="{x:Binding Sports}"/>
                </StackLayout.GestureRecognizers>
                <StackLayout Orientation="Horizontal" Padding="20,10">
                    <CheckBox IsChecked="{x:Binding Sports.IsSelected}"/>
                    <Label
                        Text="{x:Binding Sports.Name}"
                        FontAttributes="Bold" 
                        TextColor="Black" 
                        Style="{x:StaticResource MediumTextBold}"/>
                    <Label
                        Grid.Column="1"
                        Margin="10,0"
                        FontFamily="ABC"
                        FontSize="25"
                        Text="{x:Static common:ABCIcon.ArrowDown}"
                        TextColor="Black"
                        HorizontalOptions="EndAndExpand">
                        <Label.Triggers>
                            <DataTrigger
                                Binding="{x:Binding Sports.IsExpanded}"
                                TargetType="Label"
                                Value="true">
                                <Setter Property="Text" Value="{x:Static common:ABCIcon.ArrowUp}" />
                            </DataTrigger>
                        </Label.Triggers>
                    </Label>
                </StackLayout>
                <BoxView HeightRequest="1" Color="LightGray" Margin="0,-5,0,0"/>
            </StackLayout>
        </DataTemplate>
    </CollectionView.GroupHeaderTemplate>

    <CollectionView.ItemTemplate>
        <DataTemplate x:DataType="model:AthleteModel">
            <controls:TappableStack TappedCommand="{x:Binding Source={x:Reference Athletes},
                                                    Path=BindingContext.AthleteDetailsCommand}"
                                                    TappedCommandParameter="{x:Binding AthleteId}"
                                                    IsVisible="{x:Binding }">
                <StackLayout Orientation="Horizontal" Padding="20,10">
                    <CheckBox IsChecked="{x:Binding IsSelected}"/>
                    <StackLayout Spacing="5">
                        <Label 
                            VerticalOptions="Center"
                            Text="{x:Binding Name}"
                            TextColor="Black"
                            Style="{x:StaticResource SmallText}"
                            FontFamily="RM"/>
                        <Label Margin="0,-5,0,0">
                            <Label.FormattedText>
                                <FormattedString>
                                    <Span Text="{x:Static i18n:Translator.Athelete_Alias}" TextColor="Black" Style="{x:StaticResource SmallText}" FontFamily="RM"/>
                                    <Span Text=" :  " TextColor="Black" Style="{x:StaticResource SmallText}" FontFamily="RM"/>
                                    <Span Text="{x:Binding Alias}" TextColor="Black" Style="{x:StaticResource SmallText}"/>
                                </FormattedString>
                            </Label.FormattedText>
                        </Label>
                    </StackLayout>
                    <Label
                        FontFamily="ABC"
                        FontSize="Large"
                        Text="{x:Static common:ABCIcon.ArrowRight}"
                        TextColor="Black"
                        VerticalOptions="Center"
                        HorizontalOptions="EndAndExpand"/>
                </StackLayout>
                <BoxView HeightRequest="1" Color="LightGray"/>
            </controls:TappableStack>
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

方法一：通过RelativeSource关联父级分组数据 #

在分组的CollectionView中，每个子项的父级CollectionViewItem的绑定上下文就是对应的SportsModel分组。可以通过RelativeSource向上查找该父级元素，直接绑定目标属性：

<controls:TappableStack TappedCommand="{x:Binding Source={x:Reference Athletes},
                                                Path=BindingContext.AthleteDetailsCommand}"
                                                TappedCommandParameter="{x:Binding AthleteId}"
                                                IsVisible="{Binding BindingContext.Sports.IsExpanded, RelativeSource={RelativeSource AncestorType={x:Type CollectionViewItem}}}">

方法二：在AthleteModel中添加分组引用 #

如果业务逻辑允许，在AthleteModel类中新增一个指向所属SportsModel的属性：

// AthleteModel类代码
public SportsModel ParentSports { get; set; }

构建分组数据时，给每个AthleteModel实例赋值该属性，之后就能在XAML中直接绑定：

IsVisible="{Binding ParentSports.Sports.IsExpanded}"

方法三：绑定到CollectionView的GroupBindingContext #

利用CollectionView自带的GroupBindingContext属性，通过RelativeSource查找CollectionView并绑定到当前项的分组上下文：

IsVisible="{Binding GroupBindingContext.Sports.IsExpanded, RelativeSource={RelativeSource AncestorType={x:Type CollectionView}}}"

内容的提问来源于stack exchange，提问作者Endeavor