比较特定属性的两个通用列表

Question

我正在使用 VB.NET 和 .NET 2.0。

我有两个列表，我想比较对象中特定属性的列表，而不是整个对象，并创建一个新列表，其中包含一个列表中的对象，但不包含另一个列表中的对象。

myList1.Add(New Customer(1,"John","Doe")
myList1.Add(New Customer(2,"Jane","Doe")

myList2.Add(New Customer(1,"","")

上例中的结果将包含一位客户 Jane Doe，因为标识符 2 不在第二个列表中。

如何比较这两个 List 或 .NET 2.0（缺少 LINQ）中的任何 IEnumerable？

Answer 1

这是 C# 版本，VB 即将推出......

Dictionary<int, bool> idMap = new Dictionary<int, bool>();
myList2.ForEach(delegate(Customer c) { idMap[c.Id] = true; });

List<Customer> myList3 = myList1.FindAll(
    delegate(Customer c) { return !idMap.ContainsKey(c.Id); });

这是 VB 翻译。请注意，VB 在 .NET2 中没有匿名函数，因此使用 ForEach 和 FindAll 方法比标准 For Each 循环更加笨拙:

Dim c As Customer

Dim idMap As New Dictionary(Of Integer, Boolean)
For Each c In myList2
    idMap.Item(c.Id) = True
Next

Dim myList3 As New List(Of Customer)
For Each c In myList1
    If Not idMap.ContainsKey(c.Id) Then
        myList3.Add(c)
    End If
Next

Answer 2

这在 c# 2.0 中是可能的。

List<Customer> results = list1.FindAll(delegate(Customer customer)
                          {
                              return list2.Exists(delegate(Customer customer2)
                                               {
                                                   return customer.ID == customer2.ID;
                                               });
                          });

Answer 3

我想分享我的函数来比较两个对象列表：

代码：

Public Function CompareTwoLists(ByVal NewList As List(Of Object), ByVal OldList As List(Of Object))
            If NewList IsNot Nothing AndAlso OldList IsNot Nothing Then
                If NewList.Count <> OldList.Count Then
                    Return False
                End If
                For i As Integer = 0 To NewList.Count - 1
                    If Comparer.Equals(NewList(i), OldList(i)) = False Then
                        Return False
                    End If
                Next
            End If
            Return True
End Function

示例：

Dim NewList as new list (of string) from{"0","1","2","3"} 
Dim OldList as new list (of string) from{"0","1","2","3"} 
messagebox.show(CompareTwoLists(NewList,OldList)) 'return true 

Dim NewList as new list (of string) from{"0","1","2","4"} 
Dim OldList as new list (of string) from{"0","1","2","3"} 
messagebox.show(CompareTwoLists(NewList,OldList)) 'return false