How to read cell values from SelectedItems?

private void Button_Click(object sender, RoutedEventArgs e)
{
    listBox.Items.Clear();
    // Get the selected items of SfDataGrid
    var reflector = this.dataGrid.View.GetPropertyAccessProvider();
    foreach (var row in this.dataGrid.SelectedItems)
    {
        foreach (var column in dataGrid.Columns)
        {
            //Get the value from data object based on MappingName 
            var cellvalue = reflector.GetValue(row, column.MappingName);
            //Returns the display value of the cell from data object based on MappingName 
            //var displayValue = reflector.GetFormattedValue(row, column.MappingName);
            listBox.Items.Add(cellvalue.ToString());
        }
    }
}