How to change DataGridCell value programatically - wpf

Question

I have a DataGrid with some rows.Now I want change some cell style, eg:
|red| Hel |/red| |blue| lo |/blue| Everybody.
Here is my GetCell function.
public 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++)
{
var 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)
{
var row = (DataGridRow) grid.ItemContainerGenerator.ContainerFromIndex(index);
if (row != null) return row;
// 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) return null;
var presenter = GetVisualChild<DataGridCellsPresenter>(row);
if (presenter == null)
{
grid.ScrollIntoView(row, grid.Columns[column]);
presenter = GetVisualChild<DataGridCellsPresenter>(row);
}
var cell = (DataGridCell) presenter.ItemContainerGenerator.ContainerFromIndex(column);
if (cell == null)
{
grid.ScrollIntoView(row, grid.Columns[column]);
cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(column);
}
return cell;
}
public static DataGridCell GetCell(this DataGrid grid, int row, int column)
{
DataGridRow rowContainer = grid.GetRow(row);
return grid.GetCell(rowContainer, column);
}
When I set DataGridCell content with some value by grid.GetCell(1, 0).Content = "PpppPppp", and then scroll DataGrid, the value is gone!
Why?
Even the value jumps to another cell.So strange.
I want to set the cell with style, so not use the funtion about:
(this.dataGrid1.Items[0] as DataRowView)[0] = "new value";
But:
private void SetBlockStyle(TextBlock block, Dictionary<int, int> section)
{
Brush foreground = Brushes.Red;
int start = 0;
string text = block.Text;
block.Text = "";
foreach (int i in section.Keys)
{
if (text.Length <= i)
{
break;
}
block.Inlines.Add(text.Substring(start, i - start));
start = i;
block.Inlines.Add(new Run(text.Substring(i, section[i]))
{
Foreground = foreground,
FontWeight = FontWeights.Bold
});
start += section[i];
}
if (start < text.Length)
{
block.Inlines.Add(text.Substring(start, text.Length - start));
}
}
Can you give me some advice?