我正在尝试实现一个CollectionView，如下图所示。正如你所看到的，如果一个元素被选中，它在右上角有一个对应的复选标记

首先，我试图在SelectionChanged事件中找到AbstractLayout类别ID，并且已经在其中查找了名为=“showIfSelected”的元素，但是在collectionView中搜索时，我总是得到null。我已经阅读了几篇关于为什么会出现这种情况的文章，但是我还没有找到解决问题的方法。也许有人可以告诉我最终如何达到我需要的结果？
.xaml：

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage 
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:viewmodels="clr-namespace:Paraglider.MobileApp.ViewModels"
    xmlns:models="clr-namespace:Paraglider.MobileApp.Models"
    x:DataType="viewmodels:CatalogPageViewModel"
    x:Class="Paraglider.MobileApp.Pages.CatalogPage">

    <Grid BackgroundColor="#FFFEF6">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>

        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="10*" />
        </Grid.RowDefinitions>

        ...

        <ScrollView Grid.Row="1" Grid.ColumnSpan="2" Margin="20, 0" VerticalScrollBarVisibility="Never">

            <CollectionView
                x:Name="collectionView"
                Grid.Row="2" Grid.ColumnSpan="2"
                ItemsSource="{Binding Categories}"
                SelectionMode="Multiple"
                SelectionChanged="CollectionView_SelectionChanged">

                <CollectionView.Header>...</CollectionView.Header>

                <CollectionView.ItemsLayout>
                    <GridItemsLayout Orientation="Vertical" Span="{OnIdiom Default=2}" />
                </CollectionView.ItemsLayout>

                <CollectionView.ItemTemplate>
                    <DataTemplate x:DataType="models:Category">
                        <AbsoluteLayout x:Name="{Binding Id}">
                            
                            <Image 
                                Aspect="AspectFit" 
                                WidthRequest="165" 
                                Source="pzv.svg" 
                                Margin="0, 10" />
                            
                            <Image
                                x:Name="showIfSelected"
                                Aspect="AspectFit" 
                                AbsoluteLayout.LayoutBounds="130, 0, autoSize, autoSize"  
                                Source="selected_category.svg" 
                                IsVisible="True" >
                                <Image.Shadow>
                                    <Shadow Brush="Black" Offset="0, 10" Opacity="0.1" Radius="15" />
                                </Image.Shadow>
                            </Image>
                            
                        </AbsoluteLayout>
                    </DataTemplate>
                </CollectionView.ItemTemplate>

            </CollectionView>

        </ScrollView>

    </Grid>
</ContentPage>

.xaml.cs：

public partial class CatalogPage : ContentPage
{
    public CatalogPage(CatalogPageViewModel viewModel)
    {
        InitializeComponent();
        BindingContext = viewModel;
    }

    private void CollectionView_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        var prev = e.PreviousSelection.Select(x => (Category)x).ToList();
        var current = e.CurrentSelection.Select(x => (Category)x).ToList();

        var unselected = prev.ExceptBy(current.Select(x => x.Id), x => x.Id).ToList();

        foreach (var item in unselected)
        {
            var layout = this.FindByName<AbsoluteLayout>($"{item.Id}");
            var image = layout.FindByName<Image>("showIfSelected");
            image.IsVisible = false;
        }

        var selected = current.ExceptBy(prev.Select(x => x.Id), x => x.Id).ToList();

        foreach (var item in selected)
        {
            var layout = this.FindByName<AbsoluteLayout>($"{item.Id}");
            var image = layout.FindByName<Image>("showIfSelected");
            image.IsVisible = true;
        }
    }
}