Nullable 类型的转换

一直都是个头疼的问题，感谢maplye

1.The PumaCode.org Blog

public object ChangeType(object value, Type conversionType)
{
    if ( conversionType.IsGenericType &&
        conversionType.GetGenericTypeDefinition( ).Equals( typeof( Nullable<> ) ) ) {
 
        if(value == null)
            return null;
 
        System.ComponentModel.NullableConverter nullableConverter
            = new System.ComponentModel.NullableConverter(conversionType);
 
        conversionType = nullableConverter.UnderlyingType;
    }
 
    return Convert.ChangeType(value, conversionType);
}

引用：http://blog.pumacode.org/2006/05/18/using-convert-changetype-on-nullable-types/

2.Paul Wilson's .NET Blog

public class DataTypeConverter
    {
        public static object ChangeType(Type type,object value)
        {
            if ((value == null) && type.IsGenericType)
            {
                return Activator.CreateInstance(type);
            }
            if (value == null)
            {
                return null;
            }
            if (type == value.GetType())
            {
                return value;
            }
            if (type.IsEnum)
            {
                if (value is string)
                {
                    return Enum.Parse(type, value as string);
                }
                return Enum.ToObject(type, value);
            }
            if (!type.IsInterface && type.IsGenericType)
            {
                Type type1 = type.GetGenericArguments()[0];
                object obj1 = DataTypeConverter.ChangeType(type1,value);
                return Activator.CreateInstance(type, new object[] { obj1 });
            }
            if ((value is string) && (type == typeof(Guid)))
            {
                return new Guid(value as string);
            }
            if ((value is string) && (type == typeof(Version)))
            {
                return new Version(value as string);
            }
            if (!(value is IConvertible))
            {
                return value;
            }
            return Convert.ChangeType(value, type);
        }
    }

引用：http://weblogs.asp.net/pjohnson/archive/2006/02/07/437631.aspx