在c＃中按名称排序学生列表

Question

我在按字母StudentName排序学生时遇到问题。

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

OrderBy返回OrderBy。您必须遍历它：

IOrderedEnumerable

输出：

IOrderedEnumerable

Answer 2

如果未提供字符串，则类似WriteLine的函数将调用

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

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

。并且该方法的默认实现是打印类名。没有自动为您打印数组或枚举器的内容。 （即使存在，学生类也可能不会覆盖

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

。）

如果要打印数组内容，则必须自己动手编写它并调用适当的属性：

ToString()

当然，在这种情况下，您想通过命令代替枚举器：

ToString()

或使用其他人的循环，例如使用James LINQ Join解决方案。

Answer 3

当前，您正在尝试使用

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

将列表对象打印到控制台。

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

Console.WriteLine()内部调用列表对象的

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

方法。然后，对象变成其Console.WriteLine()表示形式，在您的情况下，该外观可能看起来像.ToString()。

要覆盖对象string-表示，您需要自己定义System.Linq.OrderedEnumerable2[StackOverflow.Program+Student,System.String]方法。因此，示例如下所示：

string

然后，您将可以迭代.ToString()的列表并将其表示打印到控制台：

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}";
    }
}

如果只想将每个学生的单个属性打印到控制台，则可以通过打印特定属性值来做到这一点：

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

//迭代学生并仅打印每个学生的IDforeach（列表中的var学生，按字母顺序排列）Console.WriteLine（student.StudentID）;

完整示例

Student

注

不要忘记导入

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

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

和

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}";
            }
        }

        private 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();
        }
    }
}

，因为您将需要它们来执行上述代码。

System.Collections.Generic