dotnet/maui · error · ArgumentNullException

propertyKey

Error message

propertyKey

What it means

Thrown by the public BindableObject.ClearValue(BindablePropertyKey) overload when propertyKey is null. The key-based overload exists for read-only bindable properties and dereferences propertyKey.BindableProperty, so a null key is rejected immediately.

Source

Thrown at src/Controls/src/Core/BindableObject.cs:120

			if (property.IsReadOnly)
			{
				Application.Current?.FindMauiContext()?.CreateLogger<BindableObject>()?.LogWarning($"Cannot set the BindableProperty \"{property.PropertyName}\" because it is readonly.");
				return;
			}

			ClearValueCore(property, specificity);
		}

		/// <summary>
		/// Clears any value that is previously set for a bindable property, identified by its key.
		/// </summary>
		/// <param name="propertyKey">The key that identifies the bindable property to clear the value for.</param>
		/// <exception cref="ArgumentNullException">Thrown when <paramref name="propertyKey"/> is <see langword="null"/>.</exception>
		/// <exception cref="InvalidOperationException">Thrown when <paramref name="propertyKey"/> is a read-only property.</exception>
		public void ClearValue(BindablePropertyKey propertyKey)
		{
			if (propertyKey == null)
				throw new ArgumentNullException(nameof(propertyKey));

			ClearValueCore(propertyKey.BindableProperty, SetterSpecificity.ManualValueSetter);
		}

		void ClearValueCore(BindableProperty property, SetterSpecificity specificity)
		{

			BindablePropertyContext bpcontext = GetContext(property);
			if (bpcontext == null)
				return;

			var original = bpcontext.Values.GetSpecificityAndValue();
			if (original.Key == SetterSpecificity.FromHandler)
			{
				bpcontext.Values.Remove(SetterSpecificity.FromHandler);
			}

			var newValue = bpcontext.Values.GetClearedValue(specificity);

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Pass the actual BindablePropertyKey returned when the read-only BindableProperty was created (the static readonly field).
2. Null-check the key before clearing: if (key is not null) obj.ClearValue(key);.
3. If you only have the BindableProperty, use the property-based ClearValue overload instead.

Example fix

// before
obj.ClearValue((BindablePropertyKey)null);
// after
obj.ClearValue(MyControl.ReadOnlyPropertyKey);

static void SafeClearKey(BindableObject obj, BindablePropertyKey? key)
{
    if (key is null) return;
    obj.ClearValue(key);
}

static bool IsValidKey(BindablePropertyKey? k) => k is not null;

When it happens

Trigger: Calling ClearValue((BindablePropertyKey)null) or passing a key variable that resolved to null, reaching 'throw new ArgumentNullException(nameof(propertyKey))'.

Common situations: Clearing a read-only property whose key field was never assigned; holding a BindablePropertyKey in a dictionary that returns null; refactor that renamed the key field and left the old reference null.

Related errors

• property
• targetProperty
• page
• self
• renderer

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/451be564d45e2c10. Report an issue: GitHub.