AvaloniaUI/Avalonia · error · ArgumentException

Invalid priority ${priority}

Error message

Invalid priority ${priority}

What it means

Thrown by ThrowInvalidPriority when a binding priority is outside the valid range [BindingPriority.Animation, BindingPriority.Inherited). Note: the message contains a literal '${priority}' due to an interpolation bug in the source ($ followed by {priority} instead of {priority}), so the actual priority value is NOT shown in the exception text. Priority must fall within the defined BindingPriority enum band.

Source

Thrown at src/Avalonia.Base/AvaloniaObject.cs:894

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static void ValidatePriority(BindingPriority priority)
        {
            if (priority < BindingPriority.Animation || priority >= BindingPriority.Inherited)
                ThrowInvalidPriority(priority);
        }

        private static void ThrowIfReadOnly(AvaloniaProperty property)
        {
            if (property.IsReadOnly)
            {
                throw new ArgumentException($"The property {property.Name} is readonly.");
            }
        }

        private static void ThrowInvalidPriority(BindingPriority priority)
        {
            throw new ArgumentException($"Invalid priority ${priority}", nameof(priority));
        }
    }
}

View on GitHub (pinned to 11c5427268)

Solutions

1. Use one of the named BindingPriority values (Animation, LocalValue, StyleTrigger, etc.) rather than raw ints.
2. Validate priority with the same bounds check (>= Animation && < Inherited) before calling.
3. If you see literal '${priority}' in the message, note it is a known formatting defect; inspect the priority argument in a debugger.

Example fix

// before
obj.SetValue(MyProp, value, (BindingPriority)999);

// after
obj.SetValue(MyProp, value, BindingPriority.LocalValue);

static bool IsValidPriority(BindingPriority p) =>
    p >= BindingPriority.Animation && p < BindingPriority.Inherited;

try { obj.SetValue(prop, value, priority); }
catch (ArgumentException ex) when (ex.Message.Contains("Invalid priority"))
{ obj.SetValue(prop, value, BindingPriority.LocalValue); }

When it happens

Trigger: Calling SetValue/Bind with a BindingPriority value outside the allowed band; casting an arbitrary int to BindingPriority and passing it.

Common situations: Custom binding code that hand-picks a priority; passing default(BindingPriority) in a path that expects a concrete level; numeric coercion bugs.

Related errors

• The property {property.Name} is readonly.
• Unsupported AvaloniaProperty type.
• 'name' may not contain periods.
• Object of type '{value?.GetType()}' cannot be converted to t
• Value must be less than 10.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/f59bb1e6c289d47d. Report an issue: GitHub.