Question

所以我的ArrayList看起来像这样：

        using System.Collections;
        [...]
        //in main:
        Student s01 = new Student
        {
            name = "John",
            surname = "Doa"
        };

        Student s02 = new Student
        {
            name = "John",
            surname = "Doe"
        };

        Student s03 = new Student
        {
            name = "John",
            surname = "Doi"
        };

        Student s04 = new Student
        {
            name = "John",
            surname = "Doo"
        };

        Student s05 = new Student
        {
            name = "John",
            surname = "Dou"
        };

        ArrayList studentsList = new ArrayList();
        studentsList.Add(s03);
        studentsList.Add(s04);
        studentsList.Add(s05);
        studentsList.Add(s01);
        studentsList.Add(s02);

Student.cs：

class Student : IPerson
{
    public string name;
    public string surname;

    public void Describe()
    {
        Console.WriteLine("{0} {1}", name, surname);
    }

我希望studentsList按surname排序我的对象，并在foreach循环中记下姓名+姓氏。我知道studentsList.Sort();无法工作，因为它不知道应该以何种方式将每个对象与其他对象进行比较 - 以及那个我被困的地方，因为我真的不知道如何编写使用arrayList中对象字段值的新比较器。 I甚至不知道如何开始。

我必须使用ArrayList，但我不必直接对它进行排序（我可以使用我猜测） - 最后它必须看起来像：

1. John Doa
2. John Doe
3. John Doi
4. John Doo
5. John Dou

Sort() studentsList会很棒，因为我能够做到这样的事情：

int i = 0;
foreach (Student s in studentsList)
{
   i++;
   Console.Write("{0}. ", i);
   s.Describe();
}

Answer 1

您还可以在Student中定义compareTo方法，以便能够使用studentList.Sort（）。学生班还应该扩展：IComparable

  public int CompareTo(object obj)
  {
        if (obj == null) return 1;
        Student other = obj as Student;
        if (other != null)
        {
            // Compare last names first, then by firstName
            int value = this.lastName.CompareTo(other.lastName);
            if (value == 0)
                value = this.firstName.CompareTo(other.firstName);
            return value;
        }
        else
            throw new ArgumentException("Object is not a Student");
  }

Answer 2

您可以按照以下方式执行此操作

        ArrayList studentsList = new ArrayList();
        studentsList.Add(s03);
        studentsList.Add(s04);
        studentsList.Add(s05);
        studentsList.Add(s01);
        studentsList.Add(s02);

        var studentsList2 = studentsList.Cast<Student>().OrderBy(r => r.surname).ToList();

        int i = 0;
        foreach (Student s in studentsList2)
        {
            i++;
            Console.Write("{0}. ", i);
            s.Describe();
        }

Answer 3

foreach (var student in studentsList.OfType<Student>().OrderBy(x => x.surname).ThenBy(x => x.name))
        {
            i++;
            Console.Write("{0}. ", i);
            student.Describe();
        }

按预期工作（感谢@Will，https://stackoverflow.com/users/1228/will），我没有意识到linq表达式会那么容易。话虽如此，这只是学术上的例子，因为自2005年以来，ArrayList已经过时了（@JonSkeet）。

按对象字段值排序ArrayList

3 个答案: