前言

之前我們曾寫過一篇文章 FineUI小技巧（3）表格導出與文件下載，對於在 FineUI 中導出表格數據進行了詳細描述。今天我們要更進一步，介紹下如何導出多表頭表格。

多表頭表格的標簽定義

在 ASPX 中，我們通過 GroupField 列來定義多表頭，如下所示：

<f:Grid ID="Grid1" Title="表格" EnableCollapse="true" ShowBorder="true" ShowHeader="true" Width="800px"
	runat="server" DataKeyNames="Id,Name">
	<Columns>
		<f:TemplateField ColumnID="tfNumber" Width="60px">
			<ItemTemplate>
				<span id="spanNumber" runat="server"><%# Container.DataItemIndex + 1 %></span>
			</ItemTemplate>
		</f:TemplateField>
		<f:GroupField EnableLock="true" HeaderText="分組一" TextAlign="Center">
			<Columns>
				<f:BoundField Width="100px" DataField="Name" DataFormatString="{0}" HeaderText="姓名" />
				<f:TemplateField ColumnID="tfGender" Width="80px" HeaderText="性別" TextAlign="Center">
					<ItemTemplate>
						<asp:Label ID="labGender" runat="server" Text='<%# GetGender(Eval("Gender")) %>'></asp:Label>
					</ItemTemplate>
				</f:TemplateField>
				<f:GroupField EnableLock="true" HeaderText="考試成績" TextAlign="Center">
					<Columns>
						<f:BoundField EnableLock="true" Width="80px" DataField="ChineseScore" SortField="ChineseScore" HeaderText="語文成績"
							TextAlign="Center" />
						<f:BoundField EnableLock="true" Width="80px" DataField="MathScore" SortField="MathScore" HeaderText="數學成績"
							TextAlign="Center" />
						<f:BoundField EnableLock="true" Width="80px" DataField="TotalScore" SortField="TotalScore" HeaderText="總成績"
							TextAlign="Center" />
					</Columns>
				</f:GroupField>
			</Columns>
		</f:GroupField>
		<f:BoundField ExpandUnusedSpace="True" DataField="Major" HeaderText="所學專業" />
		<f:BoundField Width="100px" DataField="LogTime" DataFormatString="{0:yy-MM-dd}" HeaderText="注冊日期" />
	</Columns>
</f:Grid>

這是一個樹狀的結構，通過 GroupField 的 Columns 集合來定義子列，從而實現多表頭的效果：

老方法已經不再奏效

如果照搬之前的邏輯，我們和容易寫出如下的導出代碼（處理數組很簡單，循環搞定）：

protected void Button1_Click(object sender, EventArgs e)
{
	Response.ClearContent();
	Response.AddHeader("content-disposition", "attachment; filename=myexcel.xls");
	Response.ContentType = "application/excel";
	Response.ContentEncoding = System.Text.Encoding.UTF8;
	Response.Write(GetGridTableHtml(Grid1));
	Response.End();
}

private string GetGridTableHtml(Grid grid)
{
	StringBuilder sb = new StringBuilder();

	sb.Append("<meta http-equiv=\"content-type\" content=\"application/excel; charset=UTF-8\"/>");


	sb.Append("<table cellspacing=\"0\" rules=\"all\" border=\"1\" style=\"border-collapse:collapse;\">");

	sb.Append("<tr>");
	foreach (GridColumn column in grid.Columns)
	{
		sb.AppendFormat("<td>{0}</td>", column.HeaderText);
	}
	sb.Append("</tr>");


	foreach (GridRow row in grid.Rows)
	{
		sb.Append("<tr>");

		foreach (GridColumn column in grid.Columns)
		{
			string html = row.Values[column.ColumnIndex].ToString();

			if (column.ColumnID == "tfNumber")
			{
				html = (row.FindControl("spanNumber") as System.Web.UI.HtmlControls.HtmlGenericControl).InnerText;
			}
			else if (column.ColumnID == "tfGender")
			{
				html = (row.FindControl("labGender") as AspNet.Label).Text;
			}


			sb.AppendFormat("<td>{0}</td>", html);
		}

		sb.Append("</tr>");
	}

	sb.Append("</table>");

	return sb.ToString();
}

打開導出的文件，我們會發現所有子列都不見了：

這樣很容易理解，因為在后台，FineUI 也是按照樹狀的結構存儲 Grid1.Columns 屬性的：

[{
    "text": "分組一",
    "columns": [{
        "text": "姓名"
    }, {
        "text": "性別"
    }, {
        "text": "考試成績",
        "columns": [{
            "text": "語文成績"
        }, {
            "text": "數學成績"
        }, {
            "text": "總成績"
        }]
    }, ]
}, {
    "text": "所學專業"
}, {
    "text": "注冊日期"
}]

樹狀結構轉換為 table 標簽

這個還真不好辦，因為 table 標簽不像它看起來那么簡單，每個單元格都可能要設置 rowspan 和 colspan，來看下我們最終需要的結構：

最終生成的 table 標簽如下所示：

<table cellspacing="0" rules="all" border="1" style="border-collapse:collapse;">
    <tr>
        <th rowspan="3"></th>
        <th colspan="5" style="text-align:center;">分組一</th>
        <th rowspan="3">所學專業</th>
        <th rowspan="3">注冊日期</th>
    </tr>
    <tr>
        <th rowspan="2">姓名</th>
        <th rowspan="2">性別</th>
        <th colspan="3" style="text-align:center;">考試成績</th>
    </tr>
    <tr>
        <th>語文成績</th>
        <th>數學成績</th>
        <th>總成績</th>
    </tr>
</table>

最終生成了 3 行數據，每一行中 th 的個數不盡相同，每個 th 的參數也不相同，看來這個轉換要自己手工做了。

實現轉換之前，我們先來總結兩個關鍵的邏輯：

1. 如果某列有子列，則更改本列的 colspan，並且增加所有父列（向上追溯）的 colspan

2. 如果下一行有數據，則增加上一行（向上追溯）中沒有子項的列的 rowspan

每個 th 在 C# 代碼中通過 object[] 來表達，比如 [考試成績] 這一列最終的結構是：

[
    1,			// rowspan
    3,			// colspan
    考試成績,	        // 當前列對象
    分組一		// 父列對象
]

邏輯點到為止，剩下的就來看代碼了，我們把邏輯封裝到自定義類中：

/// <summary>
/// 處理多表頭的類
/// </summary>
public class MultiHeaderTable
{
	// 包含 rowspan，colspan 的多表頭，方便生成 HTML 的 table 標簽
	public List<List<object[]>> MultiTable = new List<List<object[]>>();
	// 最終渲染的列數組
	public List<GridColumn> Columns = new List<GridColumn>();


	public void ResolveMultiHeaderTable(GridColumnCollection columns)
	{
		List<object[]> row = new List<object[]>();
		foreach (GridColumn column in columns)
		{
			object[] cell = new object[4];
			cell[0] = 1;    // rowspan
			cell[1] = 1;    // colspan
			cell[2] = column;
			cell[3] = null;

			row.Add(cell);
		}

		ResolveMultiTable(row, 0);

		ResolveColumns(row);
	}

	private void ResolveColumns(List<object[]> row)
	{
		foreach (object[] cell in row)
		{
			GroupField groupField = cell[2] as GroupField;
			if (groupField != null && groupField.Columns.Count > 0)
			{
				List<object[]> subrow = new List<object[]>();
				foreach (GridColumn column in groupField.Columns)
				{
					subrow.Add(new object[]
					{
						1,
						1,
						column,
						groupField
					});
				}

				ResolveColumns(subrow);
			}
			else
			{
				Columns.Add(cell[2] as GridColumn);
			}
		}

	}

	private void ResolveMultiTable(List<object[]> row, int level)
	{
		List<object[]> nextrow = new List<object[]>();

		foreach (object[] cell in row)
		{
			GroupField groupField = cell[2] as GroupField;
			if (groupField != null && groupField.Columns.Count > 0)
			{
				// 如果當前列包含子列，則更改當前列的 colspan，以及增加父列（向上遞歸）的colspan
				cell[1] = Convert.ToInt32(groupField.Columns.Count);
				PlusColspan(level - 1, cell[3] as GridColumn,groupField.Columns.Count - 1);

				foreach (GridColumn column in groupField.Columns)
				{
					nextrow.Add(new object[]
					{
						1,
						1,
						column,
						groupField
					});
				}
			}
		}

		MultiTable.Add(row);

		// 如果當前下一行，則增加上一行（向上遞歸）中沒有子列的列的 rowspan
		if (nextrow.Count > 0)
		{
			PlusRowspan(level);

			ResolveMultiTable(nextrow, level + 1);
		}
	}

	private void PlusRowspan(int level)
	{
		if (level < 0)
		{
			return;
		}

		foreach (object[] cells in MultiTable[level])
		{
			GroupField groupField = cells[2] as GroupField;
			if (groupField != null && groupField.Columns.Count > 0)
			{
				// ...
			}
			else
			{
				cells[0] = Convert.ToInt32(cells[0]) + 1;
			}
		}

		PlusRowspan(level - 1);
	}

	private void PlusColspan(int level, GridColumn parent, int plusCount)
	{
		if (level < 0)
		{
			return;
		}

		foreach (object[] cells in MultiTable[level])
		{
			GridColumn column = cells[2] as GridColumn;
			if (column == parent)
			{
				cells[1] = Convert.ToInt32(cells[1]) + plusCount;

				PlusColspan(level - 1, cells[3] as GridColumn, plusCount);
			}
		}
	}

}

其實主要的邏輯就上面提到的兩點，然后需要好幾個遞歸函數來一塊完成任務。

導出的代碼調用如下：

protected void Button1_Click(object sender, EventArgs e)
{
	Response.ClearContent();
	Response.AddHeader("content-disposition", "attachment; filename=myexcel.xls");
	Response.ContentType = "application/excel";
	Response.ContentEncoding = System.Text.Encoding.UTF8;
	Response.Write(GetGridTableHtml(Grid1));
	Response.End();
}

private string GetGridTableHtml(Grid grid)
{
	StringBuilder sb = new StringBuilder();

	MultiHeaderTable mht = new MultiHeaderTable();
	mht.ResolveMultiHeaderTable(Grid1.Columns);


	sb.Append("<meta http-equiv=\"content-type\" content=\"application/excel; charset=UTF-8\"/>");


	sb.Append("<table cellspacing=\"0\" rules=\"all\" border=\"1\" style=\"border-collapse:collapse;\">");

	foreach (List<object[]> rows in mht.MultiTable)
	{
		sb.Append("<tr>");
		foreach (object[] cell in rows)
		{
			int rowspan = Convert.ToInt32(cell[0]);
			int colspan = Convert.ToInt32(cell[1]);
			GridColumn column = cell[2] as GridColumn;

			sb.AppendFormat("<th{0}{1}{2}>{3}</th>",
				rowspan != 1 ? " rowspan=\"" + rowspan + "\"" : "",
				colspan != 1 ? " colspan=\"" + colspan + "\"" : "",
				colspan != 1 ? " style=\"text-align:center;\"" : "",
				column.HeaderText);
		}
		sb.Append("</tr>");
	}


	foreach (GridRow row in grid.Rows)
	{
		sb.Append("<tr>");

		foreach (GridColumn column in mht.Columns)
		{
			string html = row.Values[column.ColumnIndex].ToString();

			if (column.ColumnID == "tfNumber")
			{
				html = (row.FindControl("spanNumber") as System.Web.UI.HtmlControls.HtmlGenericControl).InnerText;
			}
			else if (column.ColumnID == "tfGender")
			{
				html = (row.FindControl("labGender") as AspNet.Label).Text;
			}


			sb.AppendFormat("<td>{0}</td>", html);
		}

		sb.Append("</tr>");
	}

	sb.Append("</table>");

	return sb.ToString();
}

最終導出的文件結構如下所示：