How to call a class method on a property of that class

Question

I am trying to figure out how to call a class method on a property of that class. Here are my two classes:

public class MrBase
{
    public int? Id { get; set; }
    public String Description { get; set; }
    public int? DisplayOrder { get; set; }

    public String NullIfEmpty()
    {
        if (this.ToString().Trim().Equals(String.Empty))
            return null;
        return this.ToString().Trim();
    }
}

public class MrResult : MrBase
{
    public String Owner { get; set; }
    public String Status { get; set; }

    public MrResult() {}
}

MrResult inherits from MrBase.

Now, I want to be able to call the NullIfEmpty method on any of the properties of these classes... like so:

MrResult r = new MrResult();
r.Description = "";
r.Description.NullIfEmpty();
r.Owner = "Eric";
r.Owner.NullIfEmpty();

Thanks.

Eric

Answer 1

You should write an extension method for string:

public static class StringExtensions
{
    public static string NullIfEmpty(this string theString)
    {
        if (string.IsNullOrEmpty(theString))
        {
            return null;
        }

        return theString;
    }
}

Usage:

string modifiedString = r.Description.NullIfEmpty();

If your main goal is to automatically "modify" each string property of your classes, you can achieve this using reflection. Here's a basic example:

private static void Main(string[] args)
{
    MrResult r = new MrResult
    {
        Owner = string.Empty,
        Description = string.Empty
    };

    foreach (var property in r.GetType().GetProperties())
    {
        if (property.PropertyType == typeof(string) && property.CanWrite)
        {
            string propertyValueAsString = (string)property.GetValue(r, null);
            property.SetValue(r, propertyValueAsString.NullIfEmpty(), null);
        }
    }

    Console.ReadKey();
}

Answer 2

If you want this code to be specific to your model, then you could built it into your setters with a slight modification to your NullIfEmpty method e.g.

private String _owner;

public String Owner
{
    get { return _owner; }
    set { _owner = NullIfEmpty(value); } 
}

...
public String NullIfEmpty(string str) 
{
    return str == String.Empty ? null : str;
}