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

Thrown by the same converter when value is non-null but not a bool. The converter only accepts null or bool; any other runtime type (int, string, Visibility, etc.) is rejected to surface binding-mismatch bugs loudly.

Source

Thrown at src/SamplesApp/SamplesApp.Samples/Windows_UI_Xaml_Controls/CommandBar/CommandBar_Native_With_AppBarButton_Binding.xaml.cs:51

		}
	}

	public class FromNullableBoolToCustomValueConverter : 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)
		{
			if (parameter != null)
			{
				throw new ArgumentException($"This converter does not use any parameters. You should remove \"{parameter}\" passed as parameter.");
			}

View on GitHub (pinned to 0418340488)

Solutions

Bind to a bool or bool? source property.
If the source is genuinely non-bool, add an intermediate converter that maps it to bool first, or use a converter that accepts the actual type.
Inspect value.GetType().FullName in the error message to identify the unexpected type and fix the binding path or source.

Example fix

// before - bound to an int property Count
{Binding Count, Converter={StaticResource FromNullableBoolToCustomValue}}
<!-- after - bind to a bool property, or wrap -->
{Binding HasItems, Converter={StaticResource FromNullableBoolToCustomValue}}

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 only bool / bool? sources to nullable-bool converters.
When chaining converters, ensure the upstream emits bool.
Inspect value.GetType().FullName in the message to identify the wrong type.

When it happens

Trigger: The bound source property is an int, enum, string, Visibility, or nullable-int rather than bool or bool?; the binding then hands a non-bool, non-null value to Convert.

Common situations: Binding to the wrong property (e.g. an enum or count instead of a boolean flag); a value converter chain feeding an incompatible type; source changed type during refactor without updating bindings.

Related errors

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/efb4d36c6a708a42. Report an issue: GitHub.