Validation in a cell of Gridview

Question

I am working with RadGridView (WPF) and I need to validate cell compared to other values in binding collection.

I have a object :

public class MyObject
{ 
    public DateTime DateBegin { get; set;}
    public int Value { get; set;}
}

And if I add a new row in my GridView with existing Date I want to show error message in cell.

I thought to use an ValidationRules in my cell, but i am not sure if i can compared to with others values in binding list.