When creating a custom Markup Extension that accepts parameters in WPF, the ConstructorArgument markup must be used to identify the discrete properties that match these parameters. However since this is done via a string, the compiler will not notice if there are typos.

This rule raises an issue when the string argument to ConstructorArgumentAttribute doesn’t match any parameter of any constructor.

Noncompliant Code Example

using System;

namespace myLibrary
{
  public class MyExtension : MarkupExtension
  {
    public MyExtension() { }

    public MyExtension(object value1)
    {
      Value1 = value1;
    }

    [ConstructorArgument("value2")]   // Noncompliant
    public object Value1 { get; set; }
  }
}

Compliant Solution

using System;

namespace myLibrary
{
  public class MyExtension : MarkupExtension
  {
    public MyExtension() { }

    public MyExtension(object value1)
    {
      Value1 = value1;
    }

    [ConstructorArgument("value1")]
    public object Value1 { get; set; }
  }
}