extension function return wrong confirm button when too many data can not show all and have scrollbar

refer from http://social.msdn.microsoft.com/Forums/vstudio/en-US/85fe1e60-f369-41cc-918f-e0839cc839ce/how-to-enable-button-in-specified-cell-for-datagrid-programmatically

insert and edit the confirm button will be enabled the next line, not the current line

                                int count = 0;
                                Button button = myGrid.FindChild<Button>("btnConfirm", iVPFS_Client.Server.DataGridHelper.GetRowIndex(cell), ref count);

using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Media;

    public static class DataGridExtension
    {
        public static T FindChild<T>(this DependencyObject parent, string childName, int rownum, ref int count) where T : DependencyObject
        {
            // Confirm parent and childName are valid. 
            if (parent == null) return null;

            T foundChild = null;
            int childrenCount = VisualTreeHelper.GetChildrenCount(parent);
            for (int i = 0; i < childrenCount; i++)
            {
                var child = VisualTreeHelper.GetChild(parent, i);
                // If the child is not of the request child type child
                T childType = child as T;
                if (childType == null)
                {
                    // recursively drill down the tree
                    foundChild = FindChild<T>(child, childName, rownum, ref count);

                    // If the child is found, break so we do not overwrite the found child. 
                    if (foundChild != null) break;
                }
                else if (!string.IsNullOrEmpty(childName))
                {
                    var frameworkElement = child as FrameworkElement;
                    // If the child's name is set for search
                    if (frameworkElement != null && frameworkElement.Name == childName)
                    {
                        // if the child's name is of the request name
                        count = count + 1;
                        if (count > rownum)
                        {
                            foundChild = (T)child;
                        }
                        break;
                    }
                }
                else
                {
                    // child element found.
                    foundChild = (T)child;
                    break;
                }
            }

            return foundChild;
        }


    }

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