Constructor Argument Value¶

What does this mean ?¶

WPF's ConstructorArgumentAttribute maps a property to the named constructor parameter used for XAML serialization. Its string value is metadata; it is not a parameter declaration or a requirement that every ordinary C# constructor use the attribute.

What can happen ?¶

A mismatched name can cause incorrect or failed XAML serialization/reconstruction. The precise failure depends on the XAML processor and usage. The attribute does not itself validate untrusted input or establish a security boundary.

Recommendation¶

Use the exact parameter name for the corresponding property and test the extension with the supported WPF/XAML runtime. Implement the required ProvideValue method. Keep a separate review of any objects or services the extension accesses.

Sample Code¶

This Windows/WPF example maps Value to constructor parameter value:

using System;
using System.Windows.Markup;

public sealed class ValueExtension : MarkupExtension
{
    public ValueExtension(object value) { Value = value; }

    // Incorrect mapping would be [ConstructorArgument("otherValue")].
    [ConstructorArgument("value")]
    public object Value { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return Value;
    }
}

Regression checks¶

On Windows with the target WPF runtime, load and serialize a local XAML fixture using the extension. Assert that the supplied constructor value survives the intended round trip. A normal C# compilation is not sufficient to verify all XAML metadata behavior.

References¶

• Microsoft ConstructorArgumentAttribute