title: How to get old value in PropertyGrid TypeConversion?
body: <p>I have a special case of property grid input where I would need to enter a Vector3 under a string format, let's say "0, 5, 1". I built the converter for it as such:</p>
  
  <pre><code>public class Vector3Converter : ExpandableObjectConverter
  {
      public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
      {
          return (sourceType == typeof(string));
      }
  
      public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
      {
          string[] splitted = ((string)value).Remove(" ").Split(new char[] { ',' });
  
          return new Vector3(float.Parse(splitted[0]), float.Parse(splitted[1]), float.Parse(splitted[2]));
      }
  }
  </code></pre>
  
  <p>Now this works somehow, but for another reason (I won't bother explaining, it's incredibly long, but justified - I couldn't avoid it by changing my initial design), I need to know what value was in the field before setting the new one (which somehow depends on it).</p>
  
  <p>How could I do this?</p>