How to display a popup below datagrid cell in WPF

     private double GetColumnXPosition(DataGridColumn column, DataGrid grid)
{
     double result = 0.0;

    if (grid == null)
        return result;

    for (int i = 0; i < grid.Columns.Count; i++)
    {
        DataGridColumn dgc = grid.Columns[i];
        if (dgc.Equals(column))
            break;

        result += dgc.ActualWidth;
    }
    return result;
}
private DataGrid GetRowsDataGrid(DataGridRow row)
{
    DependencyObject result = VisualTreeHelper.GetParent(row);
    while (result != null && !(result is DataGrid))
    {
        result = VisualTreeHelper.GetParent(result);
    }
    return result as DataGrid;
}

private void DgvMain_BeginningEdit(object sender, DataGridBeginningEditEventArgs e)
{
    Point newPosition = new Point();

    double rowX=0;
    DataGrid dg = GetRowsDataGrid(e.Row); //get the Row's corresponding DataGrid with the help of the VisualTreeHelper. You cant use the Column here, because it won't get added to the visual tree.
    if (dg != null)
    {
        rowX = GetColumnXPosition(e.Column, dg); //get the x position. Here you can't use .TranslatePoint because - again - it doesn't belong to the visual tree, so you have to sum up all columns width' to the column where the changes are made.
        newPosition = e.Row.TranslatePoint(new Point( DgvMain.RowHeaderWidth, e.Row.ActualHeight), this); //translate this point to a point on your main window.
    }

    if (newPosition != new Point())
    {

              Popup1.PlacementRectangle = new Rect(rowX + DgvMain.RowHeaderActualWidth, newPosition.Y - DgvMain.Margin.Top, 0, 0);

    }

    Popup1.IsOpen = true;

}


private void DgvMain_CellEditEnding(object sender, DataGridCellEditEndingEventArgs e)
{
    Popup1.IsOpen = false;
}