Question

So I have an imported file. Basically, I want to use the headers of this file to know which columns should be placed into which variable value on my class. I’d like to do this comparison via variable attributes in C#, but I’m not really sure how to approach this and set this up.

For example, say one variable in my class is public string Name; and in the imported file, one of the column headers is Name. I’d rather not use reflection to match the variable directly. How can I set an attribute on my class variable, and then use it to match with these local string header variables, and fill the correct one?

Answer 1

Here is an example program that should give you what you need. The SetOption method is what provides the reflection logic to find the field with the specified option name and set its value.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace ConsoleApplication1
{
   // This is the attribute that we will apply to the fields
   // for which we want to specify an option name.
   [AttributeUsage(AttributeTargets.Field)]
   public class OptionNameAttribute : Attribute
   {
      public OptionNameAttribute(string optionName)
      {
         OptionName = optionName;
      }

      public string OptionName { get; private set; }
   }

   // This is the class which will contain the option values that 
   // we read from the file.
   public class OptionContainer
   {
      [OptionName("Name")]
      public string MyNameField;

      [OptionName("Value")]
      public string MyValueField;
   }

   class Program
   {
      // SetOption is the method that assigns the value provided to the 
      // field of the specified instance with an OptionName attribute containing
      // the specified optionName.
      static void SetOption(object instance, string optionName, string optionValue)
      {
         // Get all the fields that has the OptionNameAttribute defined
         IEnumerable<FieldInfo> optionFields = instance.GetType()
            .GetFields()
            .Where(field => field.IsDefined(typeof(OptionNameAttribute), true));

         // Find the single field where the OptionNameAttribute.OptionName property
         // matches the provided optionName argument.
         FieldInfo optionField = optionFields.SingleOrDefault(field =>
            field.GetCustomAttributes(typeof(OptionNameAttribute), true)
            .Cast<OptionNameAttribute>().Single().OptionName.Equals(optionName));

         // If the found field is null there is no such option.
         if (optionField == null)
            throw new ArgumentException(String.Format("Unknown option {0}", optionName), "optionname");

         // Finally set the value.
         optionField.SetValue(instance, optionValue);
      }

      static void Main(string[] args)
      {
         OptionContainer instance = new OptionContainer();
         SetOption(instance, "Name", "This is the value of Name");
         SetOption(instance, "Value", "This is my value");

         Console.WriteLine(instance.MyNameField);
         Console.WriteLine(instance.MyValueField);
      }
   }
}