public virtual void AddExtraContent(ExtraContent extraContent)
{
if (!this.ExtraContents.Contains(extraContent))
{
this.ExtraContents.Add(extraContent);
}
}
public virtual void RemoveExtraContent(ExtraContent extraContent)
{
if (this.ExtraContents.Contains(extraContent))
{
this.ExtraContents.Remove(extraContent);
}
}