无法打破 foreach 循环

Question

I am using a collection to add a list of employees with add and display function like below:

class Collection<T>
{
    static List<T> list = new List<T>();
    public Collection()
    {

    }

    public bool Add(T obj, ref T u)
    {
        list.Add(obj);  
        return true;
    }

    public void Display()
    {
        bool s = false;
        foreach (T u in list)
        {
            Console.WriteLine(u.ToString());
            s = true;
            break;
        }         
    }

And a class that contains a menu:

public class EmployeeManagement : Employee
{
    Collection<Employee> emp = new Collection<Employee>();
    public void MainMenu()

    {
        Console.WriteLine("1. Import Employee");
        Console.WriteLine("2. Display Employee Information");
        Console.WriteLine("3. Search Employee");
        Console.WriteLine("4. Exit");
        Console.WriteLine("Enter Menu Option Number: ");
        int choice = Convert.ToInt32(Console.ReadLine());
        do
        {
            switch(choice)
            {
            case 1:
                ImportEmployee();
                break;
            case 2:
                emp.Display();
                break;
            }
        } while (true);


    }

    public void AddEmployee(Employee u)
    {
        u.InputEmployee();           
        if (!emp.Add(u))
        {
            Console.WriteLine("88");
        }
    }


    public void ImportEmployee()
    {

        while (true)
        {

            Console.WriteLine("================== Import Employee ============");
            Console.WriteLine("1. Salaried Employee");
            Console.WriteLine("2. Hourly Employee");
            Console.WriteLine("3. Main Menu");
            int choice = Convert.ToInt32(Console.ReadLine());
            if (choice == 1)
            {
                SalariedEmployee salEmployee = new SalariedEmployee();
                AddEmployee(salEmployee);
            }
            else if (choice == 2)
            {
                HourlyEmployee hourlyEmployee = new HourlyEmployee();
                AddEmployee(hourlyEmployee);
            }
            else
            {
                MainMenu();
                break;
            }
            Console.ReadKey();
        }

    }
}

I have added a new employee and it's has been added to my list. After that, I hit option 3 to go back to the main menu and choose display employee, it kept printing my list employee and cannot break out the loop. How can I fix this problem, I have tried to display in importemployee() menu and it worked without a problem.

Answer 1

The break in the foreach loop in Display() is OK, nothing wrong there. " break; " breaks out of the closest loop or a switch statement.

Your issue is that you can't break out of the do-while in MainMenu() and that your choice will remain 2 because you are not reading the input in the do-while.

In other words, you will break out of the foreach in Display(), you'll end up in the switch in MainMenu(), you'll break out of the switch, you'll start the do-while over again and then you will enter the Display() because your choice will still be 2. This will keep repeating itself.

I've written some comments for your code so that you can follow the flow a bit easier and added some suggestions.

    public void Display()
    {
        bool s = false;
        foreach (T u in list)
        {
            Console.WriteLine(u.ToString());
            s = true;

            //Breaks out of this loop, nothing wrong here. I would use return though, if I don't have to perform any code afterwards.
            break;
        }         
    }

   public void MainMenu()
   {
        .
        .
        .

        //Only reading choice once. Would need to handle exception
        int choice = Convert.ToInt32(Console.ReadLine());
        do
        {
            //Choice will always be what you initially selected since you are not reading it inside the do-while. If you selected two it will always be two.
            switch(choice)
            {
            case 1:
                ImportEmployee();

                //Breaks out of switch statement
                break;
            case 2:
                emp.Display();

                //Breaks out of switch statement
                break;
            }

        //Infinity loop since you have no breaks for the do-while or a condition to exit it
        } while (true);
   }

My suggestion for your do-while, if you want to use do-while, would be to have it like this.

        public void MainMenu()
        {
            Console.WriteLine("1. Import Employee");
            Console.WriteLine("2. Display Employee Information");
            Console.WriteLine("3. Search Employee");
            Console.WriteLine("4. Exit");
            Console.WriteLine("Enter Menu Option Number: ");

            //Default value 0
            int choice;
            do
            {
                //Use TryParse, it safely tries to interpret a string as a number. For string "s" it would return false, for string -1 it would return -1.
                //If an invalid string is entered, it will display a message, set choice to 0, go to the end of the loop then start over reading a key.
                //The entered string needs to be between the value of 1 and 4
                if (!int.TryParse(Console.ReadLine(), out choice) || choice > 4 || choice < 1)
                {
                    //We do not want to automatically trigger our switch with our previous value
                    choice = 0;

                    Console.WriteLine("Invalid menu selection, select 1-4");
                }

                switch (choice)
                {
                    case 1:
                        ImportEmployee();
                        break;
                    case 2:
                        emp.Display();
                        break;
                    case 3:
                        Console.WriteLine("Not implemented");
                        break;
                }
            } while (choice != 4); //Only stop the loop if we selected 4
        }

There are a lot of different ways to do this but this feels like a school assignment so I'm kind of just answering your question and not suggesting other improvements.

You also have quite a big issue in your "ImportEmployee()" that will be apparent when you fix the main menu loop. If you need a hint later I'll post in comments but try to find it yourself.

GL