How do I create a Gtk.PropertyExpression?

[Daniel15]

I'm trying to create an Adw.ComboRow. I'm using some example Python code that comes with GNOME Workbench as a reference: https://github.com/workbenchdev/demos/blob/0d46b4fbb0fa548f82fe158de4c3228c4d59da2c/src/Drop%20Down/main.py#L65

I've created my own class that extends GObject.Object for the items, and created a Gio.ListStore that uses it. That's working fine. Now I'm trying to create a PropertyExpression so that the label appears properly, but I'm stuck. There's no PropertyExpression.New method, and the PropertyExpression constructor only takes one argument (an IntPtr). I was expecting to find a PropertyExpression.New method matching this signature:

GtkExpression*
gtk_property_expression_new (
  GType this_type,
  GtkExpression* expression,
  const char* property_name
)

Is this missing from Gir.Core?

[Daniel15]

Never mind, I didn't notice that the readme says this isn't supported yet

[Daniel15]

This is what I ended up with for ComboRow as a workaround to PropertyExpression not being usable. I'm using a StringList model rather than a ListStore, and keeping a mapping from the label to the original item. Works fine as long as all labels are unique.

using Adw;
using Gtk;

namespace WebCamControl.Gtk;

/// <summary>
/// Wrapper around <see cref="ComboRow"/> that allows C# types to be used as items.
/// </summary>
/// <typeparam name="T">Type of item</typeparam>
public class CustomComboRow<T> : ComboRow
{
	private Dictionary<string, T> _labelToItem = new();

	public CustomComboRow(IntPtr ptr, bool ownedRef) : base(ptr, ownedRef) { }

	/// <summary>
	/// Gets or sets a callback to get the label for the specified item.
	/// </summary>
	public Func<T, string> LabelCallback { get; set; } = item => item.ToString();

	/// <summary>
	/// Gets or sets the list of items to show 
	/// </summary>
	/// <exception cref="ArgumentException">Thrown if multiple items have the same label</exception>
	public IEnumerable<T> Items
	{
		set
		{
			var items = value.ToArray();
			var itemCount = items.Length;
			var labelToItem = new Dictionary<string, T>(itemCount);
			var labels = new string[itemCount];

			for (var i = 0; i < itemCount; i++)
			{
				var item = items[i];
				var label = LabelCallback(item);
				labels[i] = label;
				if (!labelToItem.TryAdd(label, item))
				{
					throw new ArgumentException(
						$"Two items have the same label '{label}'. All items must have a unique label"
					);
				}
			}

			Model = StringList.New(labels);
			_labelToItem = labelToItem;
		}
	}

	/// <summary>
	/// Gets the currently selected item.
	/// </summary>
	public new T? SelectedItem
	{
		get
		{
			var label = (StringObject?)base.SelectedItem;
			return label?.String == null ? default : _labelToItem[label.String];
		}
	}
}