c# - C# 在通用列表中列出用户输入

Question

所以，我正在研究 C# 来提高自己。我正在研究通用列表，我只是试图询问用户两个选择。1 显示学生列表，2- 将学生添加到列表中（ID 是自动生成的，用户只需提供姓名）。当我运行代码时，列表总是空的。我在哪里做错了你们能帮忙吗？

class Program
{
    static void Main(string[] args)
    {
        AddStudent addStudent = new AddStudent();
        
        PrintStudentsList printStudentsList = new PrintStudentsList();
        int choice;
        
        do
        {
            Console.WriteLine("1-See the student list\n2-Add a student to the list\n3-Exit");
            choice = Int32.Parse(Console.ReadLine());
    
            if (choice == 1)
            {
                printStudentsList.PrintStudents();
            }
            else if (choice == 2)
            {
                Console.Write("Enter the Name of the Student please: ");
                string studentName = Console.ReadLine();
                        
                addStudent.Add(studentName);
            }
            else if (choice==3)
            {
                Console.WriteLine("Exiting from the program");
            }
            else
            {
                Console.WriteLine("You entered a wrong choice, please try again...");
            }
        } 
        while (choice!=3); 
    
        Console.ReadLine();
    }
}
    
    
class AddStudent
{
    private List<Students> students = new List<Students>();
    
    public List<Students>GetList()
    {
        return students;
    }
    
    private string _studentName;
             
    //public AddStudent(String studentName)
    //{
    //    _studentName = studentName;
    //}
    
    public void Add(string studentName)
    {
        Random rnd = new Random();
        int idNum = rnd.Next(1, 100);
        
        students.Add(
            new Students {Id =idNum, Name = studentName});
        }
    }
    
    class PrintStudentsList
    {
        private AddStudent addStudent = new AddStudent();
        
        public void PrintStudents()
        {
            addStudent.GetList();
            if (addStudent.GetList().Count==0)
            {
                Console.WriteLine( new EmptyListException("Student List is Empty!!!"));
            }
            else
            {
                foreach (var student in addStudent.GetList())
                {
                    Console.Write(student);
                }
            }
        }
    }
    
    class EmptyListException:Exception
    {
        public EmptyListException(string Message):base(Message)
        {
        }
    }
    
    class Students
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }
}

标签： c#visual-studio

Answer 1

你的尝试看起来有点像意大利面条代码，所以我采取了自由并重写了一点。还有几个问题。我添加了一些评论以进行进一步解释。

using System;
using System.Collections.Generic;

public class Student
{
    public string Name { get; set; }
    public int Id { get; set; }

    // Constructors are better for the programmer, because he knows what variables are required
    // And with this one, a stundent will always have a name and an id
    public Student(string name)
    {
        Name = name;
        Id = Program.rnd.Next(1, 100);
    }

    // Important, otherwise Console.WriteLine(student) only outputs "object"
    public override string ToString()
    {
        string result = $"Id: {Id} Name: {Name}";
        return result;
    }
}

public class StudentList
{
    List<Student> students;

    public StudentList()
    {
        students = new List<Student>();
    }
using System;
using System.Collections.Generic;

public class Student
{
    public string Name { get; set; }
    public int Id { get; set; }

    // Hide the default constructor, because otherwise one might forget setting the name or the id
    private Student()
    {
    }

    // Constructors are better for the programmer, because he knows what variables are required
    // And with this one, a stundent will always have a name and an id
    public Student(string name)
    {
        Name = name;
        Id = Program.rnd.Next(1, 100);
    }

    // Important, otherwise Console.WriteLine(student) only outputs "object"
    public override string ToString()
    {
        string result = $"Id: {Id} Name: {Name}";
        return result;
    }
}

public class StudentList
{
    List<Student> list;

    public StudentList()
    {
        list = new List<Student>();
    }

    public List<Student> List
    {
        get
        {
            return list;
        }

        // Dont allow setting the list from outside, so no set here
        //set
        //{
        //    students = value;
        //}
    }

    public void PrintList()
    {
        Console.WriteLine("List of students: ");
        foreach (Student student in list)
        {
            Console.WriteLine(student);
        }
        Console.WriteLine();
    }
}

class Program
{
    // Make sure you only create one instance of Random, don't instantiate it whenever you need a new value. Otherwise you risk getting the same results
    public static Random rnd = new Random();

    static void Main(string[] args)
    {
        StudentList students = new StudentList();
        int choice;

        do
        {
            Console.WriteLine("1-See the student list\n2-Add a student to the list\n3-Exit");

            // Never use .Parse, because it throws exceptions on invalid input
            // choice = Int32.Parse(Console.ReadLine());
            string input = Console.ReadLine();

            if (int.TryParse(input, out choice) == false)
            {
                // if parsing didn't work, set the choice to any value that is not one of the cases in belows switch statement
                // it will then be handled by the default switch case
                choice = -1345;
            }

            // Switches are easier to read then too many else ifs
            switch (choice)
            {
                case 1:
                    // Don't throw Exceptions when you don't have to, you could do something like this instead
                    if (students.List.Count == 0)
                    {
                        Console.WriteLine("There are no students");
                    }
                    else
                    {
                        students.PrintList();
                    }
                    break;
                case 2:
                    Student student = GetStudent();
                    students.List.Add(student);
                    break;
                // Nothing to do here, it's just to prevent entering the default case
                case 3:
                    break;
                default:
                    Console.WriteLine("You entered a wrong choice, please try again...");
                    break;
            }
            Console.WriteLine();
        } while (choice != 3);
        Console.WriteLine("Exiting from the program");

        Console.ReadLine();
    }

    private static Student GetStudent()
    {
        Console.Write("Enter the Name of the Student please: ");
        string studentName = Console.ReadLine();

        Student student = new Student(studentName);
        return student;
    }
}