unoplatform/uno · error · ArgumentException

Value must either be null or of type bool. Got {value} ({val

Error message

Value must either be null or of type bool. Got {value} ({value.GetType().FullName})

What it means

Same design as error 106 in the unit-test converter: Convert throws when value is non-null and not a bool. The test converter only accepts null or bool to keep bindings type-safe.

Source

Thrown at src/SamplesApp/SamplesApp.UnitTests.Shared/Controls/UITests/Views/Converters/FromNullableBoolToDefaultValueConverter.cs:25

using Microsoft.UI.Xaml.Media;

namespace Uno.UI.Samples.Converters
{
	public class FromNullableBoolToDefaultValueConverter : IValueConverter
	{
		public object NullOrFalseValue { get; set; }
		public object TrueValue { get; set; }

		public object Convert(object value, Type targetType, object parameter, string language)
		{
			if (parameter != null)
			{
				throw new ArgumentException($"This converter does not use any parameters. You should remove \"{parameter}\" passed as parameter.");
			}

			if (value != null && !(value is bool))
			{
				throw new ArgumentException($"Value must either be null or of type bool. Got {value} ({value.GetType().FullName})");
			}

			if (value == null || !System.Convert.ToBoolean(value, CultureInfo.InvariantCulture))
			{
				return NullOrFalseValue;
			}
			else
			{
				return TrueValue;
			}
		}

		public object ConvertBack(object value, Type targetType, object parameter, string language)
		{
			throw new NotSupportedException();
		}
	}
}

View on GitHub (pinned to 0418340488)

Solutions

  1. Bind to a bool or bool? source in the test.
  2. Insert an intermediate converter if the source is non-bool by design.
  3. Read value.GetType().FullName from the message to find the unexpected type.

Example fix

<!-- before -->
{Binding ItemCount, Converter={StaticResource Def}}
<!-- after -->
{Binding HasItems, Converter={StaticResource Def}}
Defensive patterns

Strategy: type-guard

Validate before calling

if (value is not null and not bool) throw new ArgumentException("expected bool?");

Type guard

static bool IsNullableBool(object value) => value is null or bool;

Prevention

When it happens

Trigger: The test binds a non-bool, non-null source (int, string, Visibility) to this converter.

Common situations: Test fixture bound to the wrong property; value type changed without updating the test binding.

Related errors

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/0c966f2e6db5ee5c. Report an issue: GitHub.