C#

List<T>doesn't raise an event that something was changed inside it,
as it doesn't implement IBindingList. This thus means that the bound
control can't 'observe' the datasource, so it can't know if something
changed inside List<t>.

public static class People
{
    public static List<Person> ListOfEverybody;

    public static Person CurrentPerson;

    public static bool IsPersonAlreadyEntered;

    static People()
    {
        ListOfEverybody = new List<Person>();
    }

    public static void AddPerson(string pName)
    {
        // prevent duplicates : this ain't Linq, but does use a Lambda
        IsPersonAlreadyEntered = ListOfEverybody.Exists(prsn => prsn.PersonName == pName);

        if (IsPersonAlreadyEntered) return;

        CurrentPerson = new Person(pName);
    }
}

public class Person
{
    public string PersonName { get; set; }

    public Person(string newPersonName)
    {
        PersonName = newPersonName;
        People.ListOfEverybody.Add(this);
    }

    public override string ToString()
    {
        return this.PersonName;
    }
}