在 WPF 中将值设置为数据网格单元时出现 null 异常

我创建了一个包含三个数据网格文本列的数据网格，我隐藏了一个数据网格文本列。当我尝试将值设置为隐藏的数据网格文本列时，我得到了空异常。我该如何解决这个问题。对不起，我的英语不好。提前谢谢。

我使用以下代码在隐藏的数据网格文本列中设置值。

void setValue()
{
     var tempdata = DatagridUtilities.GetCell(dgempShift,0,2);
    (tempdata.Content as TextBlock).Text = "data";
}

DatagridUtilities 的代码是

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Media;
using Microsoft.Windows.Controls;
using Microsoft.Windows.Controls.Primitives;

    public static class DatagridUtilities
    {
        private static T GetVisualChild<T>(Visual parent) where T : Visual
        {
            T child = default(T);
            int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
            for (int i = 0; i < numVisuals; i++)
            {
                Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
                child = v as T;
                if (child == null)
                {
                    child = GetVisualChild<T>(v);
                }
                if (child != null)
                {
                    break;
                }
            }
            return child;
        }
        public static DataGridRow GetSelectedRow(this DataGrid grid)
        {
            return (DataGridRow)grid.ItemContainerGenerator.ContainerFromItem(grid.SelectedItem);
        }
        public static DataGridRow GetRow(this DataGrid grid, int index)
        {
            DataGridRow row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
            if (row == null)
            {
                // May be virtualized, bring into view and try again.
                grid.UpdateLayout();
                grid.ScrollIntoView(grid.Items[index]);
                row = (DataGridRow)grid.ItemContainerGenerator.ContainerFromIndex(index);
            }
            return row;
        }
        public static DataGridCell GetCell(this DataGrid grid, DataGridRow row, int column)
        {
            if (row != null)
            {
                DataGridCellsPresenter presenter = GetVisualChild<DataGridCellsPresenter>(row);
                if (presenter == null)
                {
                    grid.ScrollIntoView(row, grid.Columns[column]);
                    presenter = GetVisualChild<DataGridCellsPresenter>(row);
                }
                DataGridCell cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(column);
                return cell;
            }
            return null;
        }
        public static DataGridCell GetCell(this DataGrid grid, int row, int column)
        {
            DataGridRow rowContainer = grid.GetRow(row);
            return grid.GetCell(rowContainer, column);
        }
    }