無法打破 foreach 循環

Question

我正在使用集合添加員工列表，添加並顯示 function，如下所示：

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;
        }         
    }

還有一個包含菜單的 class：

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();
        }

    }
}

我添加了一名新員工，並且已將其添加到我的列表中。 之后，我將選項 3 打到 go 回到主菜單並選擇顯示員工，它一直在打印我的員工列表並且無法中斷循環。 我該如何解決這個問題，我試圖在 importemployee() 菜單中顯示，它沒有問題。

Answer 1

Display() 中 foreach 循環的中斷是可以的，那里沒有錯。 “ break; ” 跳出最近的循環或 switch 語句。

您的問題是您無法在 MainMenu() 中跳出 do-while 並且您的選擇將保持為 2，因為您沒有在 do-while 中讀取輸入。

換句話說，您將在 Display() 中跳出 foreach，最終進入 MainMenu() 中的 switch，您將跳出 switch，然后重新開始 do-while您將輸入 Display()，因為您的選擇仍然是 2。這將不斷重復。

我為您的代碼寫了一些注釋，以便您可以更輕松地遵循流程並添加一些建議。

    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);
   }

如果你想使用 do-while，我對你的 do-while 的建議是這樣。

        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
        }

有很多不同的方法可以做到這一點，但這感覺就像一個學校作業，所以我只是回答你的問題，而不是建議其他改進。

您的“ImportEmployee()”中還有一個相當大的問題，當您修復主菜單循環時會很明顯。 如果您稍后需要提示，我會在評論中發布，但請嘗試自己找到。

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