如何让用户选择如何使用变量对其列表进行排序？
用户输入的信息可以按升序和降序的多种方式排序，我试图让用户选择他想要查看数据的方式：
那么有没有办法设置一个变量，用户输入和排序数据，而不是多次重复代码，具体取决于输入，如：
var empName = el.Select(i => new { i.ID, i.FullName }); if(emsort.Text="text1") empName.OrderBy(i.text1); else if... 通过做一些更短的事情：
string sort=emsort.Text ; empName.OrderBy(sort);
如果您的问题中的用户是某个调用您的函数的软件，那么用户就会知道el序列中对象的类型：他知道el序列中的元素是哪些属性，并且他知道他希望如何订购它们。
为什么不让这个用户给你在keySelector中使用的keySelector ？
创建扩展function：
static class QueryableExtensions { IQueryable SelectAndSort(this IQueryable> selector, Expression> sortKeySelector, System.ComponentModel.ListSortDirection sortDirection) { var selectBeforeOrdering = myRepository.el.Select(selector); // note: this is still an IQueryable, only the query has been made, // the database is not accessed yet! IQueryable result = (sortDirection == ListSortDirectrion.Ascending) ? // sort in ascending order: selectBeforeOrdering.OrderBy(sortKeySelector) : // else: selec in descending order: selectBeforeOrdering.OrderByDescending(sortKeySelector); return result; } }
用法：假设您的用户知道您的el ，并且他想要几个字段，按照您的el某个属性排序
using (var myDbContext = new DbContext(...)) { IQueryable myEls = myDbContext.el; var mySelectedItems = myEls.SelectAndSore( // selector: what properties do I as a user want? el => new { Id = el.Id, FullName = el.FullName, ... // other desired properties }, // sortSelector: how do I want my selected items to be sorted? selectedItem => selectedItem.FullName, // direction: ListSortDirection.Descending); // note: until now the database has not been accessed // only the Expression of the query has been created. // depending on what you want as a result: ToList / ToArray / First / ... return mySelectedItems.ToList(); }
另一方面，如果您的用户不是软件，而是操作员，他必须选择他希望订购项目的列，他必须有一种方法告诉计算机应该对哪个列进行排序。
这通常通过单击列来完成。 另一种方法可以是在combobox中选择一个值。 无论如何，您必须将某些内容附加到列或包含sortKeySelector的combobox值：
class MySortableColumn : DataGridViewColumn // or whatever column class you are using { public Expression> SortKeySelector{get;set;} }
现在，您有几个列，每个列都显示MyDisplayedItem的一个属性：
var columnId = new MySortableColumn() { SortKeySelector = displayedItem => myDisplayedItem.Id, }; var columnFullName = new MyStortableColumn() { SortKeySelector = displayedItem => myDisplayedItem.Id, } // etc.
每当操作员单击一列时，都会提取sortKey并将其用作参数来对项目进行排序：
void SortColumn(SortableColumn column) { var sortedItems = Sort(column.SortKeySelector, ListSortOrder...); Display(sortedItems); }
如果我理解你的问题，你想要使用存储在emsort.Text的属性名称动态排序，那么你可以使用表达式：
假设empName是IEnumerable ，那么使用：
private static Func GetSortable(string sortablePoperty) { var param = Expression.Parameter(typeof(Employee), "e"); var member = Expression.Property(param, sortablePoperty); Expression memberAsObject = Expression.Convert(member, typeof(object)); return Expression.Lambda>(memberAsObject, param).Compile(); }
然后使用它：
string sort=emsort.Text ; empName.OrderBy(GetSortable(sort));
如果empName是IQueryable ，那么使用：
private static Expression> GetSortable(string sortablePoperty) { var param = Expression.Parameter(typeof(Employee), "e"); var member = Expression.Property(param, sortablePoperty); Expression memberAsObject = Expression.Convert(member, typeof(object)); return Expression.Lambda>(memberAsObject, param); }
正如我所假设的， el已实现（例如，它不仅仅是数据库的入口点），因此您可以使用reflection：
var sort = emsort.Text; PropertyInfo property = null; var sortedData = el.Select(i => new { i.ID, i.FullName }) .OrderBy(x => { property = property ?? x.GetType().GetProperty(sort); return property.GetValue(x); }).ToList();
这是我必须写的代码的一部分：
if (emord.Text == "Ascending") { if (emsort.Text == "ID") { var empName = el.Select(i => new { i.ID, i.FullName }).OrderBy(x => x.ID); var empNamenAmp = el.Select(i => new { i.ID, i.FullName, i.Salary, i.Currency, i.Per }).OrderBy(x => x.ID); var empNamenAmpnwh = el.Select(i => new { i.ID, i.FullName, i.Salary, i.Currency, i.Per, i.Hours }).OrderBy(x => x.ID); var empNamenwh = el.Select(i => new { i.ID, i.FullName, i.Hours }).OrderBy(x => x.ID); var empNamenbd = el.Select(i => new { i.ID, i.FullName, i.Date }).OrderBy(x => x.ID); var empNamenad = el.Select(i => new { i.ID, i.FullName, i.Location }).OrderBy(x => x.ID); var empNamenpn = el.Select(i => new { i.ID, i.FullName, i.PhoneNb }).OrderBy(x => x.ID); var empNamena = el.Select(i => new { i.ID, i.FullName, i.Age }).OrderBy(x => x.ID); if (empfilcomb.Text == "Name") { dispfil.Clear(); foreach (var x in empName) dispfil.Text += x.ID + ", " + x.FullName + Environment.NewLine; } else if (empfilcomb.Text == "Name and Amount paid") { dispfil.Clear(); foreach (var x in empNamenAmp) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Salary + " " + x.Currency + " " + x.Per + Environment.NewLine; } else if (empfilcomb.Text == "Name and Work Hours") { dispfil.Clear(); foreach (var x in empNamenwh) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Hours + Environment.NewLine; } else if (empfilcomb.Text == "Name,Amount paid and Work Hours") { dispfil.Clear(); foreach (var x in empNamenAmpnwh) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Salary + " " + x.Currency + " " + x.Per + ", " + x.Hours + Environment.NewLine; } else if (empfilcomb.Text == "Name and Birthday") { dispfil.Clear(); foreach (var x in empNamenbd) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Date + Environment.NewLine; } else if (empfilcomb.Text == "Name and Address") { dispfil.Clear(); foreach (var x in empNamenad) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Location + Environment.NewLine; } else if (empfilcomb.Text == "Name and Phone Number") { dispfil.Clear(); foreach (var x in empNamenpn) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.PhoneNb + Environment.NewLine; } else if (empfilcomb.Text == "Name and Age") { dispfil.Clear(); foreach (var x in empNamena) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Age + Environment.NewLine; } } else if (emsort.Text == "Name") { var empName = el.Select(i => new { i.ID, i.FullName }).OrderBy(x => x.FullName); var empNamenAmp = el.Select(i => new { i.ID, i.FullName, i.Salary, i.Currency, i.Per }).OrderBy(x => x.FullName); var empNamenAmpnwh = el.Select(i => new { i.ID, i.FullName, i.Salary, i.Currency, i.Per, i.Hours }).OrderBy(x => x.FullName); var empNamenwh = el.Select(i => new { i.ID, i.FullName, i.Hours }).OrderBy(x => x.FullName); var empNamenbd = el.Select(i => new { i.ID, i.FullName, i.Date }).OrderBy(x => x.FullName); var empNamenad = el.Select(i => new { i.ID, i.FullName, i.Location }).OrderBy(x => x.FullName); var empNamenpn = el.Select(i => new { i.ID, i.FullName, i.PhoneNb }).OrderBy(x => x.FullName); var empNamena = el.Select(i => new { i.ID, i.FullName, i.Age }).OrderBy(x => x.FullName); if (empfilcomb.Text == "Name") { dispfil.Clear(); foreach (var x in empName) dispfil.Text += x.ID + ", " + x.FullName + Environment.NewLine; } else if (empfilcomb.Text == "Name and Amount paid") { dispfil.Clear(); foreach (var x in empNamenAmp) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Salary + " " + x.Currency + " " + x.Per + Environment.NewLine; } else if (empfilcomb.Text == "Name and Work Hours") { dispfil.Clear(); foreach (var x in empNamenwh) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Hours + Environment.NewLine; } else if (empfilcomb.Text == "Name,Amount paid and Work Hours") { dispfil.Clear(); foreach (var x in empNamenAmpnwh) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Salary + " " + x.Currency + " " + x.Per + ", " + x.Hours + Environment.NewLine; } else if (empfilcomb.Text == "Name and Birthday") { dispfil.Clear(); foreach (var x in empNamenbd) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Date + Environment.NewLine; } else if (empfilcomb.Text == "Name and Address") { dispfil.Clear(); foreach (var x in empNamenad) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Location + Environment.NewLine; } else if (empfilcomb.Text == "Name and Phone Number") { dispfil.Clear(); foreach (var x in empNamenpn) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.PhoneNb + Environment.NewLine; } else if (empfilcomb.Text == "Name and Age") { dispfil.Clear(); foreach (var x in empNamena) dispfil.Text += x.ID + ", " + x.FullName + ", " + x.Age + Environment.NewLine; } }
我问是否有一个更短的方法来做：我可以使用的东西。 似乎没有，但非常感谢帮助，我确定你们提供的是有用的。