Runtime search attributes

This article introduces a general method for dynamically accessing and extracting property values ​​of a class.

Use special method

Define a common method that accepts type parameters:

public string GetDomainName()

Inside the method:

• Use typeof(T).GetCustomAttributes to retrieve custom attributes:

    var dnAttribute = typeof(T).GetCustomAttributes(
      typeof(DomainNameAttribute), true
    ).FirstOrDefault() as DomainNameAttribute;

• If the property exists, its value is returned:

    if (dnAttribute != null)
    {
      return dnAttribute.Name;
    }

• Otherwise, return null:

    return null;

  ]

Utility Extension Method

For broader applicability, generalize this method to handle any attribute:

public static class AttributeExtensions
{
    public static TValue GetAttributeValue(
        this Type type, 
        Func valueSelector) 
        where TAttribute : Attribute
}

Inside the extension method:

• Retrieve custom properties:

    var att = type.GetCustomAttributes(
      typeof(TAttribute), true
    ).FirstOrDefault() as TAttribute;

• If the attribute exists, use the provided valueSelector to extract the required value:

  ]

    if (att != null)
    {
      return valueSelector(att);
    }

• Otherwise, return the default value of this type:

    return default(TValue);

  ]

Usage Example

• Retrieve DomainName attribute of MyClass:

string name = typeof(MyClass).GetDomainName();

• Retrieve any attribute value of MyClass using the extension method:

string name = typeof(MyClass)
    .GetAttributeValue((DomainNameAttribute dna) => dna.Name);