gvDetail.CustomSummaryCalculate += GvDetail_CustomSummaryCalculate; //实现自定义汇总

#region 自定义汇总

gvDetail.OptionsView.ShowFooter = true;
gvDetail.Columns["Quantity"].SummaryItem.SummaryType = SummaryItemType.Custom; //到这里会触发事件
gvDetail.Columns["Quantity"].SummaryItem.DisplayFormat = "特殊合计:{0}";
gvDetail.UpdateSummary(); //因为先绑定了数据又设置了汇总，可以手动触发一次计算

#endregion

/// <summary>
/// 自定义汇总
/// </summary>
private void GvDetail_CustomSummaryCalculate(object sender, CustomSummaryEventArgs e)
{
    //只有当GridSummaryItem的类型为Custom时，才会触发事件
    GridSummaryItem gridSummaryItem = e.Item as GridSummaryItem;
    if (gridSummaryItem.FieldName == "Quantity")
    {
    
        //第1阶段：开始
        if (e.SummaryProcess == DevExpress.Data.CustomSummaryProcess.Start){
            e.TotalValueReady = true; //设置此项可直接进入Finalize，跳过耗时的Calculate
        }

        //第2阶段：计算中，会遍历所有行
        if (e.SummaryProcess == DevExpress.Data.CustomSummaryProcess.Calculate)
        {
            //因为在Start设置了e.TotalValueReady = true; 所以这里不会执行
        }
    
    
        //在Finalize进行赋值，也就是循环到最后一行时通过对背后的数据源进行计算一次性赋值
        if (e.SummaryProcess == CustomSummaryProcess.Finalize)
        {
            //取出数据源，可能已过滤
            var filteredRows = gvDetail.DataController.GetAllFilteredAndSortedRows();

            //通过Linq进行筛选计算
            var query = from r in filteredRows.Cast<DataRowView>()
                        where !r.Row["ProductFullName"].ToString().Contains("日薪") && !r.Row["ProductFullName"].ToString().Contains("QT-") //日薪和QT不统计
                        select r;

            var result = query.Sum(c => float.Parse(c.Row["Quantity"] + ""));

            e.TotalValue = result;
        }
    }
}

//定义汇总存放变量
int customSum;

/// <summary>
/// 自定义汇总事件
/// </summary>
private void gridView1_CustomSummaryCalculate(object sender, DevExpress.Data.CustomSummaryEventArgs e)
{
    int summaryID = Convert.ToInt32((e.Item as GridSummaryItem).Tag);
    GridView gridView = sender as GridView;

    //初始化阶段，汇总值清零 
    if (e.SummaryProcess == CustomSummaryProcess.Start)
    {
        customSum = 0;
    }

    //计算阶段，会便利所有行，当前行为e.RowHandle
    if (e.SummaryProcess == CustomSummaryProcess.Calculate)
    {
        bool isSelected = (bool)gridView.GetRowCellValue(e.RowHandle, "Selected");
        switch (summaryID)
        {
            case 1: // The total summary calculated against the 'CurrentApplyQuantity' column. 
                if (isSelected) customSum += Convert.ToInt32(e.FieldValue);
                break;
        }
    }

    //计算完成，赋值
    if (e.SummaryProcess == CustomSummaryProcess.Finalize)
    {
        switch (summaryID)
        {
            case 1:
                e.TotalValue = customSum;
                break;
        }
    }
}