如何從基於OrderBy“屬性”的集合中返回IOrderedEnumerable

Question

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();
        }
    }
}

我希望能夠使用類似於以下內容的語法...

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

有成千上萬個如何將排序，過濾后的結果放入新的List，Collection，ObservableCollection等的示例，但是如果您現有的集合已經響應事件，則會自動添加新對象以響應通知，用戶操作，新數據來自服務器等），那么所有功能要么“丟失”，要么必須被“添加”，以使新的List，Collection，ObservableCollection等能夠偵聽原始集合，以某種方式與所有原始集合已經了解並處理的各種更新，屬性等...我希望能夠使原始的“ EmployeeCollection”簡單地在所請求的SortOrder中拋出“ Employee”對象。

我想對“ SortOrder”屬性的語法進行“野蠻猜測”，其原因是希望使SortOrder屬性的語法類似於lambda表達式的orderby部分，該團隊其他開發人員習慣於通過查看System.Linq.Enumerable中的擴展方法類似於以下內容： public static IOrderedEnumerable<TSource> OrderBy<ToSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector);

我是Linq，lambda等的新手，如果我因某種原因錯過了Linq / Expression Trees，謂詞，匿名代表等某些關鍵方面，而其他人則認為很明顯，請向我道歉。

Answer 1

當您不使用ThenBy -type操作（ IOrderedEnumerable<T>接口真正添加的所有操作）時，此方法有效。 請參見C＃：如何實現IOrderedEnumerable <T>以獲得支持該解決方案的解決方案。

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
}