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class Employee
{
    public string Name {get;set;}
    public int employee_id {get;set}
    public int Age {get;set}
}

Class EmployeeCollection : IEnumerable, IEnumerable<Employee>, IOrderedEnumerable<Employee>
{
    public Expression<Func<Employee, dynamic>> SortOrder {get;set;}
    protected Dictionary<int,Employee> EmployeeById = new Dictionary<int,Employee>();
    public void AddEmployee(Employee ePassed)
    {
        EmployeeById[ePassed.employee_id] = ePassed;
    }
    public IEnumerator<Employee> GetEnumerator()
    {
      foreach (int id in EmployeeByID.Keys)
      {
        yield return EmployeeById[id];
      }
    }
    IEnumerator IEnumerable.GetEnumerator()
    {
      return this.GetEnumerator();
    }
    public IOrderedEnumerable<Employee> CreateOrderedEnumerable<TKey>(Func<Employee, TKey> KeySelector, IComparer<TKey> comparer, bool descending)
    {
      if (descending)
          return this.OrderByDescending(KeySelector, comparer);
      else
          return this.OrderBy(KeySelector, comparer);
    }
    public IEnumerable<Employee> OrderedObjects
    {
        if (this.SortOrder == null)
            return (IEnumerable<Employee>)this;  // No Sort Order applied
        else
        {
          // How do I get the "parameters" from SortOrder to pass into CreateOrderedEnumerable?
          throw new NotImplementedException();
        }
    }
}

我希望能够使用类似于以下的语法...

EmployeeCollection.SortOrder = (x => x.Name);
foreach (Employee e in EmployeeCollection.OrderedObjects)
{
  // Do something in the selected order
}

有数千个示例说明如何将排序、过滤等结果放入新的列表、集合、ObservableCollection 等，但如果您现有的集合已经响应事件，则自动添加新对象以响应通知、用户操作、新数据从服务器等进来，然后所有这些功能要么“丢失”，要么必须“添加”以使新的 List、Collection、ObservableCollection 等监听原始集合，以便以某种方式与所有的保持同步原始集合已经知道和处理的各种更新、属性等......我希望能够让原始的“EmployeeCollection”简单地在请求的 SortOrder 中分发“Employee”对象......

我对“SortOrder”属性的语法做了一个“疯狂的猜测”，基于希望使 SortOrder 属性的语法类似于团队中其他开发人员习惯使用的 lambda 表达式的 orderby 部分。 System.Linq.Enumerable 中的扩展方法类似于以下内容： public static IOrderedEnumerable<TSource> OrderBy<ToSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector);

我是 Linq、lambda 等的新手，如果我不知何故错过了 Linq/表达式树、谓词、匿名代表等其他人认为显而易见的关键方面，请提前道歉。

4

1 回答 1

1

这在您不使用ThenBy-type 操作时有效（这些都是IOrderedEnumerable<T>真正添加的接口）。请参阅C#：如何实现 IOrderedEnumerable<T>以获得支持该解决方案的解决方案。

public class Employee
{
    public string Name {get;set;}
    public int employee_id {get;set;}
    public int Age {get;set;}
}

public class EmployeeCollection : IEnumerable, IEnumerable<Employee>, IOrderedEnumerable<Employee>
{
    public Func<Employee, object> SortOrder {get;set;}
    public Func<Employee, bool> Filter {get;set;}
    protected Dictionary<int,Employee> EmployeeById = new Dictionary<int,Employee>();
    public void Add(Employee ePassed)
    {
        EmployeeById[ePassed.employee_id] = ePassed;
    }
    public IEnumerator<Employee> GetEnumerator()
    {
        var employees = EmployeeById.Keys.Select(id => this.GetEmployee(id));
        if (Filter != null)
            employees = employees.Where(Filter);
        if (SortOrder != null)
            employees = employees.OrderBy(SortOrder);
        return employees.GetEnumerator();
    }
    public Employee GetEmployee(int id)
    {
        return EmployeeById[id];
    }
    IEnumerator IEnumerable.GetEnumerator()
    {
      return this.GetEnumerator();
    }
    public IOrderedEnumerable<Employee> CreateOrderedEnumerable<TKey>(Func<Employee, TKey> KeySelector, IComparer<TKey> comparer, bool descending)
    {
      throw new NotImplementedException();
    }
}

// this is some code you might use to test this:
var EmployeeCollection = new EmployeeCollection
{
    new Employee { employee_id = 1, Age = 20, Name = "Joe" },
    new Employee { employee_id = 2, Age = 30, Name = "Thomas" },
    new Employee { employee_id = 3, Age = 25, Name = "Robert" },
};
EmployeeCollection.SortOrder = x => x.Age;
EmployeeCollection.Filter = x => x.Name.Length > 4;
foreach (Employee e in EmployeeCollection)
{
    // do something
}
于 2013-10-24T21:00:19.197 回答