How can I correctly retrieve the selected item in a CollectionView's SelectionChangedCommand in C#?

When using the CollectionView’s SelectionChangedCommand, the command parameter is not the selected item itself but a SelectionChangedEventArgs instance. That means doing a simple cast to your item type will result in a null value. To resolve this, update your command to extract the selected item from the event arguments.

Below is an example of how you can modify your command:

CSHARPCopied
public NameMatchViewModel()
{
    ImageItemTappedCommand = new Command((obj) =>
    {
        try
        {
            // Cast the parameter to SelectionChangedEventArgs.
            var args = obj as SelectionChangedEventArgs;
            if (args == null)
            {
                Debug.WriteLine("SelectionChangedEventArgs is null");
                return;
            }

            // Get the selected item. With SelectionMode="Single", you can get the first item.
            var selectedItem = args.CurrentSelection.FirstOrDefault() as NameMatchList;
            if (selectedItem == null)
            {
                Debug.WriteLine("Selected item is null");
                return;
            }

            // Reset background colors.
            foreach (var item in ImageItems)
            {
                item.ImageBGColor = Colors.White;
            }

            // Set the new background color for the selected item.
            selectedItem.ImageBGColor = Color.FromArgb("#0091da");

            // Storing values in Preferences.
            if (Utility.IsInternet())
            {
                Preferences.Default.Set("NameMatchImageList_Image", selectedItem.imageUrl);
            }
            else
            {
                Preferences.Default.Set("NameMatchImageList_Image", selectedItem.FullImageUrl);
            }
            Preferences.Default.Set("NameMatchImageList_Name", selectedItem.name);
            Preferences.Default.Set("ImageItem", selectedItem);

            isImageSelected = true;
            if (isImageSelected && isNameSelected)
            {
                // If both image and name are selected, start the matching process.
                StartNameMatchCheck(selectedItem);
            }
        }
        catch (Exception imagetapEx)
        {
            Debug.WriteLine("imagetapEx:>>" + imagetapEx);
        }
    });
}

Key Points:

• The SelectionChangedEventArgs provides two lists: one for the removed items and one for the current selection.
• For single selection mode, the current selection will contain the single selected item (or be empty).
• Using SelectedItem binding can be an alternative, as it directly gives you the selected item. If you intend to use a command, make sure you extract the selected item from the event args.

By casting the command parameter to SelectionChangedEventArgs and extracting the first item from the CurrentSelection, you’ll be able to work with the selected item without encountering a null reference exception.