Repeater 資料匯出 Excel 實作：伺服器端產生 HTML 表格輸出

核心原理

利用 `Response.ContentType = "application/vnd.ms-excel"` 輸出 HTML `

完整實作步驟

1. 前端 Repeater 結構

<asp:Repeater ID="rptCatalog" runat="server">
    <HeaderTemplate><table border="1"><tr><th>ID</th><th>Name</th></tr></HeaderTemplate>
    <ItemTemplate><tr><td><%# Eval("ID") %></td><td><%# Eval("Name") %></td></tr></ItemTemplate>
    <FooterTemplate></table></FooterTemplate>
</asp:Repeater>
<asp:Button ID="btnExport" runat="server" Text="匯出 Excel" OnClick="btnExport_Click" />

2. 後端匯出邏輯

protected void btnExport_Click(object sender, EventArgs e) {
    Response.Clear();
    Response.Buffer = true;
    Response.ContentEncoding = System.Text.Encoding.UTF8;
    Response.Charset = "";
    Response.ContentType = "application/vnd.ms-excel";
    Response.AddHeader("Content-Disposition", "attachment;filename=Catalog_" + DateTime.Now.ToString("yyyyMMddHHmmss") + ".xls");

    // 讓 Repeater 重新渲染到 StringWriter
    using (var sw = new System.IO.StringWriter()) {
        using (var hw = new System.Web.UI.HtmlTextWriter(sw)) {
            rptCatalog.RenderControl(hw);
        }
        Response.Output.Write(sw.ToString());
    }
    Response.Flush();
    Response.End();
}

// 必須覆寫 VerifyRenderingInServerForm，否則 RenderControl 會拋出例外
public override void VerifyRenderingInServerForm(Control control) { }

進階：支援多工作表、樣式、欄寬的 NPOI/EPPlus 方案

HTML 輸出雖簡單但有限制：無法設定欄寬、儲存格格式、多工作表、公式。正式專案建議改用：

• NPOI：開源、支援 .xls/.xlsx、無需安裝 Office
• EPPlus：功能豐富、效能佳、.xlsx 專用
• ClosedXML：API 直覺、建立於 OpenXML SDK 之上

NPOI 範例片段

var workbook = new HSSFWorkbook(); // .xls 用 HSSF，.xlsx 用 XSSF
var sheet = workbook.CreateSheet("Catalog");
var headerRow = sheet.CreateRow(0);
headerRow.CreateCell(0).SetCellValue("ID");
headerRow.CreateCell(1).SetCellValue("Name");

int rowIdx = 1;
foreach (var item in catalogList) {
    var row = sheet.CreateRow(rowIdx++);
    row.CreateCell(0).SetCellValue(item.ID);
    row.CreateCell(1).SetCellValue(item.Name);
}
sheet.AutoSizeColumn(0); sheet.AutoSizeColumn(1);

using (var ms = new MemoryStream()) {
    workbook.Write(ms);
    Response.BinaryWrite(ms.ToArray());
}

方案選擇建議