Question

I’m building some stuff out using Attributes. One thing I’d really like to implement as an attribute is a convert a string to this property's type using this function. Right now, I have this:

    public delegate object ParameterConverter(string val);

    [AttributeUsage(AttributeTargets.Property)]
    public class ParameterConverterAttribute : ParameterBaseAttribute
    {
        ParameterConverter Converter;
        public ParameterConverterAttribute(ParameterConverter converter)
        {
            Converter=converter;
        }
        public object Convert(string val)
        {
            return Converter(val);
        }
    }

And I use it like so:

public class Tester
{
    [ParameterConverter(new ParameterConverter(TestConverter)] //error here
    public int Foo{get;set;}
    static object TestConverter(string val)
    {
      return 10;
    }
}

However, .Net or at least C# doesn’t appear to support this kind of thing. It appears that delegates inside of attributes doesn’t work.

Is there any workarounds to this issue or a good way to deal with this problem?

Answer 1

No Delegates cannot be passed as an argument to an Attribute. The Supported types are :

1. Object
2. Type
3. Enum
4. Single Dimentional Array
5. bool, byte, float char, double, int, long, string …. etc.

But as it supports Type as well as strings, you can pass a Type and the name of the method to create a delegate inside the Attribute class.

public delegate object ParameterConverter(string val);

[AttributeUsage(AttributeTargets.Property)]
public class ParameterConverterAttribute : ParameterBaseAttribute
{
    public ParameterConverter Converter { get; set; }
    public ParameterConverterAttribute(Type delegateType, string method)
    {
     try{ // Important as GetMethod can throw error exception or return null
        this.Converter = (ParameterConverter)Delegate.CreateDelegate(delegateType, delegateType.GetMethod(method));
      }
      catch { } 
    }
    public object Convert(string val)
    {
        if(this.Converter != null)
             return Converter(val);
    }
}

And now you can use it like :

public class Tester
{
    [ParameterConverter(typeof(ParameterConverter), "TestConverter"] 
    public int Foo{get;set;}
    static object TestConverter(string val)
    {
      return 10;
    }
}

I hope this would help you.