如何在xamarin forms中获取可绑定布局数据模板选择器中的列表大小

public class MyDataTemplateSelector : DataTemplateSelector
{
    public DataTemplate Template1 { get; set; }
    public DataTemplate Template2 { get; set; }

    protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
    {
        if (item is List<string> list && list.Count > 5)
        {
            return Template1;
        }
        else
        {
            return Template2;
        }
    }
}

<ContentPage.Resources>
    <ResourceDictionary>
        <DataTemplate x:Key="Template1">
            <!-- 定义模板1的内容 -->
        </DataTemplate>
        <DataTemplate x:Key="Template2">
            <!-- 定义模板2的内容 -->
        </DataTemplate>
        <local:MyDataTemplateSelector x:Key="MyDataTemplateSelector"
                                      Template1="{StaticResource Template1}"
                                      Template2="{StaticResource Template2}" />
    </ResourceDictionary>
</ContentPage.Resources>

<StackLayout BindableLayout.ItemsSource="{Binding Items}"
             BindableLayout.ItemTemplateSelector="{StaticResource MyDataTemplateSelector}">
    <!-- 绑定布局的内容 -->
</StackLayout>