dotnet/maui · error · ArgumentException

EnumPicker: EnumType property must be enumeration type

Error message

EnumPicker: EnumType property must be enumeration type

What it means

This is a second copy of the EnumPicker sample used in CollectionView gallery pages. It has identical logic: the EnumType bindable property's propertyChanged callback rejects non-enum Types with ArgumentException because the picker populates its ItemsSource via Enum.GetValues, which requires an actual enumeration.

Source

Thrown at src/Controls/samples/Controls.Sample/Pages/Controls/CollectionViewGalleries/ScrollModeGalleries/EnumPicker.cs:22

namespace Maui.Controls.Sample.Pages.CollectionViewGalleries.ScrollModeGalleries
{
	class EnumPicker : Picker
	{
		public static readonly BindableProperty EnumTypeProperty =
			BindableProperty.Create(nameof(EnumType), typeof(Type), typeof(EnumPicker),
				propertyChanged: (bindable, oldValue, newValue) =>
				{
					EnumPicker picker = (EnumPicker)bindable;

					if (oldValue != null)
					{
						picker.ItemsSource = null;
					}
					if (newValue != null)
					{
						if (!((Type)newValue).GetTypeInfo().IsEnum)
							throw new ArgumentException("EnumPicker: EnumType property must be enumeration type");

						picker.ItemsSource = Enum.GetValues((Type)newValue);
					}
				});

		public Type EnumType
		{
			set => SetValue(EnumTypeProperty, value);
			get => (Type)GetValue(EnumTypeProperty);
		}
	}
}

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Ensure only enum types are assigned: `picker.EnumType = typeof(ScrollMode);`
2. Guard before assignment: `if (candidateType.GetTypeInfo().IsEnum) picker.EnumType = candidateType;`
3. If binding, constrain the source property to return only enum Types.

Example fix

// before
picker.EnumType = typeof(string);

// after
picker.EnumType = typeof(ScrollMode);

var candidateType = typeof(ScrollMode);
if (candidateType.GetTypeInfo().IsEnum)
    picker.EnumType = candidateType;

static bool IsEnumType(Type? type) => type?.GetTypeInfo().IsEnum ?? false;

When it happens

Trigger: Assigning a non-enum Type to this EnumPicker's EnumType property. Occurs when binding EnumType to a gallery option backed by a non-enum type, or programmatically setting it incorrectly.

Common situations: Sample/gallery code that binds EnumType to a loosely-typed property. Copy-paste of the EnumPicker into a new gallery without verifying the bound type is an enum. Type resolution issues from reflection or dynamic code.

Related errors

• EnumPicker: EnumType property must be enumeration type
• Pin must have a Label to be added to a map
• Value is an invalid value for {property.PropertyName}
• mode is not a valid BindingMode
• RootComponent requires a value for its Selector property, bu

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/76c4a66b0291d785. Report an issue: GitHub.