这星期把Grid导出Excel又重写封装了一次，对于简单的导出干脆就用前台的配置列直接导出，写成了这样

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> OnExcelDown()
{
    //得到数据
    var res = await GetData();
    //导出
    Grid1.OutputExcel(res);
    return ResultAsync();
}

重新获取数据还是有必要的，前台的数据不可信，OutputExcel 主要实现了重置列头（按前台Grid的列头），文件转为byte[]，保存文件输出服务器路径；这里记录下关键路径

1. 数据源转DataTable 并 重置列名称

这里其实是两部分操作，我放在一块了，因为没有拆开的需求

1.1 得到前台的列名和字段对照

参考 FineUICoreMVC使用SignalR.InvokeAsync执行前台JS ，很容易就写出一个得到JObject键值对的方法，很优雅

C#
public static async Task<JObject> FGetColumnsAsync(this string f, string[] field = null)
{
	field ??= new string[] { "field", "text" };
	var fun = $" return F.ui['{f}'].columns.filter(m=>m.columnType=='renderfield' && m.isVisible())";
	string fields = string.Join(",", field);
	string map = $".map(({{ {fields} }}) => ({{ {fields} }}))";
	string reduce = $".reduce((acc, item) => ({{ ...acc, [item.field]: item.text }}), {{}})";
	fun = fun + map + reduce + ";";
	var res = await FineUIAjaxHelpEx.GetHubMessage(fun);
	return JObject.Parse(res) ?? new JObject(); //返回 {DataField:HeaderText}
}

1.2 重置数据源

需要判断数据源的类型 是Table 还是 model；如果是model 需要兼容二级属性或多级属性

C#
public static DataTable ToDataTable(this GridAjaxHelper Grid, object dataSource, JObject Columns = null)
{
	DataTable dataTable2 = null;
	if (Columns == null) Columns = Grid.GetColumnsAsync().Result;
	if (dataSource is DataView || dataSource is DataSet || dataSource is DataTable)
	{
		dataTable2 = TableRewrite(dataSource, Columns);
	}
	else if (dataSource is IEnumerable)
	{
		dataTable2 = ((IEnumerable)dataSource).ToDataTable(Columns);
	}
	return dataTable2;
}

C#
private static DataTable TableRewrite(object dataSource, JObject Columns)
{
	DataTable dataTable2;
	//将dataSource转换为DataTable
	if (dataSource is DataView)
	{
		dataTable2 = ((DataView)dataSource).Table;
	}
	else if (dataSource is DataSet)
	{
		dataTable2 = ((DataSet)dataSource).Tables[0];
	}
	else
	{
		dataTable2 = (DataTable)dataSource;
	}
	//按照 Columns 将 dataTable2的列表替换
	foreach (var item in Columns)
	{
		var colName = item.Value.ToString();
		var col = item.Key.ToString();
		if (dataTable2.Columns.Contains(col))
		{
			dataTable2.Columns[col].ColumnName = colName;
		}
	}
	//按照 dataTable2的列 使用 Columns 将表替换 其他的列就删掉了
	var tabalecolumns = dataTable2.Columns.Cast<DataColumn>().Select(column => column.ColumnName).ToList();
	foreach (string item in tabalecolumns)
	{
		if (!Columns.Values().Contains(item))
		{
			dataTable2.Columns.Remove(item);
		}
	}

	return dataTable2;
}

C#
public static DataTable ToDataTable(this IEnumerable collection, JObject Columns)
{
	DataTable dataTable = new DataTable();

	//循环 Columns 的建 然后 循环 collection 使用 ObjectUtil.GetPropertyValue 找到对应的值
	foreach (var item in Columns)
	{
		var colName = item.Value.ToString();
		dataTable.Columns.Add(colName);
	}

	//循环 Columns 的建 然后 循环 collection 使用 ObjectUtil.GetPropertyValue 找到对应的值
	foreach (var msitem in collection)
	{
		var row = dataTable.NewRow();
		foreach (var item in Columns)
		{
			var colName = item.Value.ToString();
			var col = item.Key.ToString();
			var val = ObjectUtil.GetPropertyValue(msitem, col);
			row[colName] = val;
		}
		dataTable.Rows.Add(row);
	}

	return dataTable;
}

2. 将重置后的数据转为byte

这里使用NPOI将DataTable转为byte[]

略

3. 保存文件并下载

保存文件

C#
//...略
using (FileStream fs = new FileStream(excelPath, FileMode.Create, FileAccess.Write))
{
	await fs.WriteAsync(data, 0, data.Length);
}

//excel文件保存的相对路径，提供前端下载
var relativePositioning = "/UploadFile/" + folder + "/" + excelFileName;
return relativePositioning;

C#
public async Task SaveExcelAndDown(byte[] data, string excelName, string hubid = "")
{
        //保存文件路径
	var outpath = await SaveExcel(data, excelName);
        //转为实际路径
	var uploadPath = FineUICore.PageContext.WebRootPath + outpath;
	string fileName = Path.GetFileName(uploadPath);
        //抛出js
	await SignalRHelper.ExecuteScript($"downloadFile('{outpath}','{fileName}');", hubid);
}

这里使用js完成下载

js
downloadFile = function (url, fileName) {
	let link = document.createElement('a');
	link.href = url;
	link.download = fileName;
	link.click();
}

4. 作为Gird的行为

因为只针对Grid控件，所以导出Exlce的应该作为Grid本身提供的一个方法，所以要扩展到Grid上

C#
public static void OutputExcel(this GridAjaxHelper Grid, object dataSource, JObject Columns = null, string title = null)
{
        //重置数据源
	var dt = Grid.ToDataTable(dataSource, Columns);
        //得到标题最为Excel标题
	if (string.IsNullOrEmpty(title)) title = Grid.GetTitleAsync().Result;

	//别忘了这句
        System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);
	var data = NPOIHelper.ExportDataTableToExcel(dt, title, "Sheet1", "1");
        //得到当前的Controller
	var thiscontroller = Commons.PageContext.Current.GetCurrentController();
	if (thiscontroller != null)
	{
		thiscontroller.SaveExcelAndDown(data, title).Wait();
	}
}

因为我的SaveExcelAndDown方法在BaseController中，扩展的OutputExcel方法是静态的，我又懒的写事件，所以用到了获取当前Controller实例的方法，.NetCore本身不提供该方法；其实是在过滤器中放的：

C#
/// <summary>
/// 获取当前控制器
/// </summary>
/// <param name="httpContext"></param>
/// <returns></returns>
public static BaseController GetCurrentController(this HttpContext httpContext)
{
	if (httpContext.Items.TryGetValue("CurrentController", out var controllerObj) &&
	controllerObj is BaseController baseController)
	{
		return controllerObj as BaseController;
	}
	return null;
}

C#
public class ParameterOverwrite : ActionFilterAttribute
{
	/// <summary>
        /// 回发时
	/// </summary>
	/// <param name="filterContext"></param>
	public override void OnActionExecuting(ActionExecutingContext filterContext)
	{
		if (filterContext.Controller is Microsoft.AspNetCore.Mvc.Controller controller)
		{
                        //把当前的Controller存起来
			filterContext.HttpContext.Items["CurrentController"] = controller;
		}
	}
        ...
}

C#
services.AddControllersWithViews().AddMvcOptions(options =>
{
        //过滤器
	options.Filters.Add<ParameterOverwrite>();
}).AddRazorRuntimeCompilation();

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