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

FromNullableBoolToReverseBoolConverter.Convert throws when value is non-null and not a bool, enforcing the nullable-bool-only contract before inverting.

Source

Thrown at src/SamplesApp/SamplesApp.UnitTests.Shared/Controls/UITests/Views/Converters/FromNullableBoolToReverseBoolConverter.cs:22

using System.Text;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Data;
using Microsoft.UI.Xaml.Media;

namespace Uno.UI.Samples.Converters
{
	public class FromNullableBoolToReverseBoolConverter : IValueConverter
	{
		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})");
			}

			var valueToConvert = value != null && System.Convert.ToBoolean(value, CultureInfo.InvariantCulture);

			return !valueToConvert;
		}

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

View on GitHub (pinned to 0418340488)

Solutions

Bind to a bool / bool? source.
Pre-convert with another converter if the source is non-bool.
Check value.GetType().FullName in the message.

Example fix

<!-- before -->
{Binding Status, Converter={StaticResource Rev}}
<!-- after -->
{Binding IsActive, Converter={StaticResource Rev}}

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

Bind bool / bool? sources only.
Use value.GetType().FullName from the message to diagnose.

When it happens

Trigger: Binding a non-bool source (int, enum, string, Visibility) to this reverse converter.

Common situations: Wrong binding path; source property type changed; value converter chain feeding an incompatible type.

Related errors

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/bb537b4ddce60790. Report an issue: GitHub.