visualTree.cs

public static T GetVisualChildByType<T>(this DependencyObject referenceVisual) where T : DependencyObject
{
    DependencyObject child = null;
    for (Int32 i = 0; i < VisualTreeHelper.GetChildrenCount(referenceVisual); i++)
    {
        child = VisualTreeHelper.GetChild(referenceVisual, i) as DependencyObject;
        if (child != null && child is T)
        {
            break;
        }
        else if (child != null)
        {
            child = GetVisualChildByType<T>(child);
            if (child != null && child is T)
            {
                break;
            }
        }
    }
    return child as T;
}