dotnet/maui · error · ArgumentNullException

targetProperty

Error message

targetProperty

What it means

Thrown by the public BindableObject.IsSet(BindableProperty) when targetProperty is null. The method uses an inline null-coalescing throw (GetContext(targetProperty ?? throw new ArgumentNullException(nameof(targetProperty)))) because it needs a real property to look up the value context.

Source

Thrown at src/Controls/src/Core/BindableObject.cs:248

				{
					var pair = context.Values.GetSpecificityAndValue();
					result.IsSet = pair.Key != SetterSpecificity.DefaultValue;
					result.Value = (T)pair.Value;
				}
			}

			return resultArray;
		}

		/// <summary>
		/// Determines whether or not a bindable property exists and has a value set.
		/// </summary>
		/// <param name="targetProperty">The bindable property to check if a value is currently set.</param>
		/// <returns><see langword="true"/> if the target property exists and has been set. Otherwise <see langword="false"/>.</returns>
		/// <exception cref="ArgumentNullException">Thrown when <paramref name="targetProperty"/> is <see langword="null"/>.</exception>
		public bool IsSet(BindableProperty targetProperty)
		{
			var bpcontext = GetContext(targetProperty ?? throw new ArgumentNullException(nameof(targetProperty)));
			if (bpcontext == null)
				return false;
			if ((bpcontext.Attributes & BindableContextAttributes.IsDefaultValueCreated) == BindableContextAttributes.IsDefaultValueCreated)
				return true;
			return bpcontext.Values.GetSpecificity() != SetterSpecificity.DefaultValue;
		}

		/// <summary>
		/// Determines whether a bindable property has been set by a local value, style, binding, or other non-default specificity.
		/// Unlike IsSet, default-value creation does not count as explicit.
		/// </summary>
		/// <param name="targetProperty">The bindable property to check if a value is explicitly set.</param>
		/// <returns><see langword="true"/> if the target property exists and has been explicitly set. Otherwise <see langword="false"/>.</returns>
		/// <exception cref="ArgumentNullException">Thrown when <paramref name="targetProperty"/> is <see langword="null"/>.</exception>
		internal bool IsSetExplicitly(BindableProperty targetProperty)
		{
			var bpcontext = GetContext(targetProperty ?? throw new ArgumentNullException(nameof(targetProperty)));
			return bpcontext is not null && bpcontext.Values.GetSpecificity() != SetterSpecificity.DefaultValue;

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Pass a non-null BindableProperty (e.g. VisualElement.IsVisibleProperty).
2. Guard the call: if (prop is not null && obj.IsSet(prop)) { ... }.
3. Resolve the BindableProperty from the correct type so it is never null.

Example fix

// before
bool set = obj.IsSet(maybeNullProp);
// after
bool set = maybeNullProp is not null && obj.IsSet(maybeNullProp);

static bool SafeIsSet(BindableObject obj, BindableProperty? p)
    => p is not null && obj.IsSet(p);

static bool IsValidProperty(BindableProperty? p) => p is not null;

When it happens

Trigger: Calling IsSet(null) or IsSet(prop) where prop evaluates to null, so the '?? throw' expression fires.

Common situations: Checking whether a property is set via a resolver that returned null; guarding against a property that may not exist on the current type; passing a BindableProperty from another type by mistake.

Related errors

• property
• propertyKey
• page
• self
• renderer

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/d0fe00edff894709. Report an issue: GitHub.