.NET - Get default value for a reflected PropertyInfo

Question

This is really stumping me today. I\'m sure its not that hard, but I have a System.Reflection.PropertyInfo object. I want to set its value based on the result of a database

Answer 1

Try the following methods, which I have written and tested against thousands of types:

    /// 

    /// [ public static T GetDefault< T >() ]
    /// 
    /// Retrieves the default value for a given Type
    /// 
    /// The Type for which to get the default value
    /// The default value for Type T
    /// 
    /// If a reference Type or a System.Void Type is supplied, this method always returns null.  If a value type 
    /// is supplied which is not publicly visible or which contains generic parameters, this method will fail with an 
    /// exception.
    /// 
    /// 
    public static T GetDefault()
    {
        return (T) GetDefault(typeof(T));
    }

    /// 

    /// [ public static object GetDefault(Type type) ]
    /// 
    /// Retrieves the default value for a given Type
    /// 
    /// The Type for which to get the default value
    /// The default value for 
    /// 
    /// If a null Type, a reference Type, or a System.Void Type is supplied, this method always returns null.  If a value type 
    /// is supplied which is not publicly visible or which contains generic parameters, this method will fail with an 
    /// exception.
    /// 
    /// 
    public static object GetDefault(Type type)
    {
        // If no Type was supplied, if the Type was a reference type, or if the Type was a System.Void, return null
        if (type == null || !type.IsValueType || type == typeof(void))
            return null;

        // If the supplied Type has generic parameters, its default value cannot be determined
        if (type.ContainsGenericParameters)
            throw new ArgumentException(
                "{" + MethodInfo.GetCurrentMethod() + "} Error:\n\nThe supplied value type <" + type +
                "> contains generic parameters, so the default value cannot be retrieved");

        // If the Type is a primitive type, or if it is another publicly-visible value type (i.e. struct), return a 
        //  default instance of the value type
        if (type.IsPrimitive || !type.IsNotPublic)
        {
            try
            {
                return Activator.CreateInstance(type);
            }
            catch (Exception e)
            {
                throw new ArgumentException(
                    "{" + MethodInfo.GetCurrentMethod() + "} Error:\n\nThe Activator.CreateInstance method could not " +
                    "create a default instance of the supplied value type <" + type +
                    "> (Inner Exception message: \"" + e.Message + "\")", e);
            }
        }

        // Fail with exception
        throw new ArgumentException("{" + MethodInfo.GetCurrentMethod() + "} Error:\n\nThe supplied value type <" + type + 
            "> is not a publicly-visible type, so the default value cannot be retrieved");
    }

The first (generic) version of GetDefault is of course redundant for C#, since you may just use the default(T) keyword.

Enjoy!