在c#中按姓名对学生列表进行排序[关闭]

Question

我无法按StudentName 的字母顺序对学生进行排序。

List<Student> studentList = new List<Student>() { 
                new Student() { StudentID = 1, StudentName = "John", Age = 18, Country = "Poland"  } ,
                new Student() { StudentID = 2, StudentName = "Steve",  Age = 22, Country = "Poland"  } ,
                new Student() { StudentID = 3, StudentName = "Bill",  Age = 18, Country = "USA"  } ,
                new Student() { StudentID = 4, StudentName = "Ram" , Age = 20, Country = "USA"  } ,
                new Student() { StudentID = 5, StudentName = "Ron" , Age = 21, Country = "Germany"  } 
            };

var listAlphabetically = studentList.OrderBy(x=>x.StudentName);  
            Console.WriteLine(listAlphabetically);

Answer 1

目前您正在尝试使用Console.WriteLine() 将序列对象listAlphabetically 直接打印到控制台。

var listAlphabetically = studentList.OrderBy(x => x.StudentName);  
Console.WriteLine(listAlphabetically);

Console.WriteLine() 在内部调用对象.ToString()-方法。该对象被转换为它的string-representation，然后将打印到控制台。在您的情况下，这可能看起来像这样：System.Linq.OrderedEnumerable2[StackOverflow.Program+Student,System.String]。

要覆盖对象string-representation，您需要自己定义.ToString() 方法。因此，一个示例可能如下所示：

public class Student
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
    public string Country { get; set; }

    public override string ToString()
    {
        return $"StudentID: {this.StudentID} - StudentName: {this.StudentName} - Age: {this.Age} - Country: {this.Country}";
    }
}

然后您将能够迭代Students 的序列并将它们的表示打印到控制台：

var listAlphabetically = studentList.OrderBy(x => x.StudentName);

// iterate students and print them to the console
foreach (var student in listAlphabetically)                   
    Console.WriteLine(student);

如果您只想将每个学生的单个属性打印到控制台，您可以执行以下操作：

var listAlphabetically = studentList.OrderBy(x => x.StudentName);

// iterate students and print only the ID of each student
foreach (var student in listAlphabetically)                   
    Console.WriteLine(student.StudentID);

完整示例

using System;
using System.Collections.Generic;
using System.Linq;

namespace StackOverflow
{
    public class Program
    {
        public class Student
        {
            public int StudentID { get; set; }
            public string StudentName { get; set; }
            public int Age { get; set; }
            public string Country { get; set; }

            public override string ToString()
            {
                return $"StudentID: {this.StudentID} - StudentName: {this.StudentName} - Age: {this.Age} - Country: {this.Country}";
            }
        }

        public static void Main(string[] args)
        {
            List<Student> studentList = new List<Student>() {
                new Student() { StudentID = 1, StudentName = "John", Age = 18, Country = "Poland"  } ,
                new Student() { StudentID = 2, StudentName = "Steve",  Age = 22, Country = "Poland"  } ,
                new Student() { StudentID = 3, StudentName = "Bill",  Age = 18, Country = "USA"  } ,
                new Student() { StudentID = 4, StudentName = "Ram" , Age = 20, Country = "USA"  } ,
                new Student() { StudentID = 5, StudentName = "Ron" , Age = 21, Country = "Germany"  }
            };

            var listAlphabetically = studentList.OrderBy(x => x.StudentName);

            // iterate students and print them to the console
            foreach (var student in listAlphabetically)
                Console.WriteLine(student);

            // keep console open
            Console.ReadKey();
        }
    }
}

注意

不要忘记导入System.Collections.Generic 和System.Linq namespace，因为您将需要它们来执行上述代码。

using System.Collections.Generic;
using System.Linq;

Answer 2

OrderBy 返回IOrderedEnumerable。你必须遍历它：

var listAlphabetically = studentList.OrderBy(x => x.StudentName);

foreach (var student in listAlphabetically)
{
    Console.WriteLine($"Name: {student.StudentName}, Age: {student.Age}, Country: {student.Country}");
}

输出：

Name: Bill, Age: 18, Country: USA
Name: John, Age: 18, Country: Poland
Name: Ram, Age: 20, Country: USA
Name: Ron, Age: 21, Country: Germany
Name: Steve, Age: 22, Country: Poland

Answer 3

如果没有给出字符串，WriteLine 等函数将调用ToString()。其默认实现是打印类名。没有自动为您打印 Array 或 Enumerator 的内容。 （即使有，Student 类也可能没有覆盖ToString()）。

如果你想打印数组内容，你必须自己迭代它并调用适当的属性：

foreach(Student current in studentList ){
    Console.WriteLine(current.StudentName);
}

当然，在您的情况下，您希望使用排序来迭代枚举器：

foreach(Student current in listAlphabetically){
    Console.WriteLine(current.StudentName);
}

或使用其他人的循环，例如使用 James LINQ 加入解决方案。