这个 要明说是 模板加入的还是 单纯的 复选框列

如果是复选框咧 直接遍历列 转换即可

如果是 模板列的话  可以采用

foreach (var item in dgReportList.Items)
            {
                DataGridTemplateColumn templeColumn = dgReportList.Columns[0] as DataGridTemplateColumn;
                FrameworkElement fwElement = dgReportList.Columns[0].GetCellContent(item) ;
                CheckBox cBox = templeColumn.CellTemplate.FindName("cBoxSelected", fwElement) as CheckBox
 ;
                if (cBox != null)
                {
                    cBox.IsChecked = cBoxSelectedAll.IsChecked;
                }
            }