Question

I’ve the following attribute:

class HandlerAttribute : System.Attribute
{
    public string MainName { get; private set; }
    public string SubName { get; private set; }

    public HandlerAttribute(string pValue, bool pIsMain) {
        if (pIsMain) MainName = pValue;
        else SubName = pValue;
    }
}

And this is the way I use the attribute

[Handler("SomeMainName", true)]
class Class1 {

    [Handler("SomeSubName", false)]
    void HandleThis() {
       Console.WriteLine("Hi");
    }
}

What I want to achieve is that I import the MainName value from the parent class attribute into the method defined inside the class.

I hope that someone can help me with this 🙂

Thanks in advance

Answer 1

I would advice to write a helper method for this, basically it isn’t possible by default because you don’t have access to the attribute’s target.

Code

[AttributeUsage(AttributeTargets.All, Inherited = false, AllowMultiple = true)]
sealed class HandlerAttribute : Attribute
{
    public string MainName { get; private set; }
    public string SubName { get; private set; }

    public HandlerAttribute(string pValue, bool pIsMain) {
        if (pIsMain) MainName = pValue;
        else SubName = pValue;
    }

    public HandlerAttributeData GetData(MemberInfo info)
    {
        if (info is Type)
        {
            return new HandlerAttributeData(MainName, null);
        }

        HandlerAttribute attribute = (HandlerAttribute)info.DeclaringType.GetCustomAttributes(typeof(HandlerAttribute), true)[0];

        return new HandlerAttributeData(attribute.MainName, SubName);
    }
}


class HandlerAttributeData
{
    public string MainName { get; private set; }
    public string SubName { get; private set; }

    public HandlerAttributeData(String mainName, String subName)
    {
        MainName = mainName;
        SubName = subName;
    }
}

Usage

        HandlerAttribute att = (HandlerAttribute)typeof(App).GetCustomAttributes(typeof(HandlerAttribute), true)[0];
        HandlerAttributeData data = att.GetData(typeof(App));

You can use it with any member and if you write a extension method you can make it even shorter.