Except()方法需要两个集合。它返回一个新集合，其中包含来自第一个集合的元素，该元素在第二个集合（参数集合）中不存在。
IList<string> strList1 = new List<string>(){"One", "Two", "Three", "Four", "Five" };
IList<string> strList2 = new List<string>(){"Four", "Five", "Six", "Seven", "Eight"};
var result = strList1.Except(strList2);
foreach(string str in result)
Console.WriteLine(str);One Two Three
Except扩展方法不返回复杂类型集合的正确结果。您需要实现IEqualityComparer接口，以便从Except方法获得正确的结果。
为 Student 类实现 IEqualityComparer 接口，如下所示:
public class Student
{
public int StudentID { get; set; }
public string StudentName { get; set; }
public int Age { get; set; }
}
class StudentComparer : IEqualityComparer<Student>
{
public bool Equals(Student x, Student y)
{
if (x.StudentID == y.StudentID && x.StudentName.ToLower() == y.StudentName.ToLower())
return true;
return false;
}
public int GetHashCode(Student obj)
{
return obj.StudentID.GetHashCode();
}
}现在，您可以在Except扩展方法中通过StudentComparer类，以获取正确的结果：
示例：C#对象类型为的Except()方法IList<Student> studentList1 = new List<Student>() {
new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
new Student() { StudentID = 2, StudentName = "Steve", Age = 15 } ,
new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } ,
new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 }
};
IList<Student> studentList2 = new List<Student>() {
new Student() { StudentID = 3, StudentName = "Bill", Age = 25 } ,
new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 }
};
var resultedCol = studentList1.Except(studentList2,new StudentComparer());
foreach(Student std in resultedCol)
Console.WriteLine(std.StudentName);John Steve
C # & VB.Net 查询语法不支持 Except 运算符。但是，您可以对查询变量使用 Distinct 方法，或者将整个查询包装到括号中，然后调用 Except ()。