C＃：方法故障（没有封闭循环可以中断或继续）

Question

Newb here working there way toward being a hobbyist.

My current project uses methods, classes, list to display books and comments and to allow users to enter their own comments in a console view. I've built my classes and they are working at this time so I've expunged them for the moment to expose my current problem as clearly as possible. get at my problem which is that I felt my program was getting kind of big quickly so it seemed like a good idea to move some of the code into a method which i called 'Select'. Before i moved the code into the select method, it worked fine/as expected. But now i'm getting error when i test: no enclosing loop out of which to break

The specific error happens on the else if (command == "e"){break;} line

I've tried swapping the keyword 'break' for 'continue', but that did not work. I've looked around the net and stackoverflow, but not found anything that i can understand well enough with my level of understanding to resolve (I'm still a newb).

Code:

    class Program
{
    public void Play(){
        Announcer(" \n\nProgram Name Goes Here \n\n");

        while (true)
        {
            /*
             * Allow user to display director of books (Three)
             * allow user to select specific book with any comments it might have (2-4 comments)
             * Allow user to enter a specific comment
             * display book with new new added comment
             * Allow user to exit book
             * */
            Select();                
        Console.Read();
        }
    }


    public void Announcer(String strTxt){Console.Write(strTxt);}

    public String GetString(String strData){
        Console.WriteLine(strData);
        return Console.ReadLine();//traffic control => back to program
    }

    public void Select(){
        String command = GetString(" \n\n(V)eiw, (S)elect, (C)omment, (R)emove, (E)xit").ToLower();

            if (command == "v")
            { Announcer(" \n\nEnter listing: ");
              //ViewDirectory();//call view directory here
            }

            else if (command == "c")
            { Announcer(" \n\nEnter comment: "); }

            else if (command == "s")
            {                   
                //we want to do a selectString method that returns length of selects here
                String select = GetString(" \n\n(1)st Selection, (2)nd Selection, (3)rd book, (E)xit").ToLower();
                if (select == "1")
                { Announcer(" \n\nDisplay book info + allow for user comment entering"); }

                else if (select == "2")
                { Announcer(" \n\nDisplay book info + allow for user comment entering"); }

                else if (select == "3")
                { Announcer(" \n\nDisplay book info + allow for user comment entering"); }                
            }

            else if (command == "e") { break; }
            else { Console.WriteLine("\n\nOopsy, I don't know that command! \n\n"); }
        }
    }

    //public void ViewDirectory(){
    //    Console.WriteLine("stuff");

    //}

Answer 1

好吧，您不在循环中，因此要终止该方法的执行，关键字为“ return”

Answer 2

After you refactored your code, it's no longer aware that it's inside of a while loop, so the break keyword is unnecessary.

You were using break to terminate the program, so you'll need to do something else to exit the while loop. There are multiple ways you could refactor, but you could try:

while (true)
{
    var command
      = GetString(" \n\n(V)eiw, (S)elect, (C)omment, (R)emove, (E)xit").ToLower();

    if (command == "e")
        break;

    Select(command);

    Console.Read();
}

Pass command to Select() , so most of your logic is still in the other method... just don't test for command == "e" in Select() .

Answer 3

Just omit the break; statement as there is no need for it, it is only required when you want to quit executing a loop.

Answer 4

Problem : you can't break from if block as it is not enclosed in any loop .

Solution : You just return the status of the condition from the if block to ensure the loop breaks from the caller function .

1. if the command equals to "e" return the true so that caller breaks the loop.
2. else return the false so that loop continues.

 class Program
{
    public void Play(){
    Announcer(" \n\nProgram Name Goes Here \n\n");

    while (true)
    {
        /*
         * Allow user to display director of books (Three)
         * allow user to select specific book with any comments it might have (2-4 comments)
         * Allow user to enter a specific comment
         * display book with new new added comment
         * Allow user to exit book
         * */
         if(Select())
             break;   //break if you get return value of Select() as true
         Console.Read();
     }
}


 public bool Select(){
    String command = GetString(" \n\n(V)eiw, (S)elect, (C)omment, (R)emove, (E)xit").ToLower();

        if (command == "v")
        { Announcer(" \n\nEnter listing: ");
          //ViewDirectory();//call view directory here
         return false;
        }

        else if (command == "c")
        { Announcer(" \n\nEnter comment: ");  return false;}

        else if (command == "s")
        {                   
            //we want to do a selectString method that returns length of selects here
            String select = GetString(" \n\n(1)st Selection, (2)nd Selection, (3)rd book, (E)xit").ToLower();
            if (select == "1")
            { Announcer(" \n\nDisplay book info + allow for user comment entering"); }

            else if (select == "2")
            { Announcer(" \n\nDisplay book info + allow for user comment entering"); }

            else if (select == "3")
            { Announcer(" \n\nDisplay book info + allow for user comment entering"); }                

             return false;           
           }

        else if (command == "e") { return true; }
        else { Console.WriteLine("\n\nOopsy, I don't know that command! \n\n"); return 
          false; }
    }
}

Answer 5

break keywords work with loop or switch block. In Select method there is no such statements. you can return true/false from Select method and inside play method you can call break base on return value;

if(Select())
{
     break;
}

Answer 6

I would update your Select method to return a boolean value indicating that the input was valid. Then, you can set the while condition as follows:

while (Select())
{
    /*
     * Allow user to display director of books (Three)
     * allow user to select specific book with any comments it might have (2-4 comments)
     * Allow user to enter a specific comment
     * display book with new new added comment
     * Allow user to exit book
     * */     
    Console.Read();
}

I would also discourage the use of many else if's like you have, and update them to use switch/case instead. For case s, you can also make that into a separate method.

public bool Select()
{
    bool isValid = true;
    String command = GetString(" \n\n(V)eiw, (S)elect, (C)omment, (R)emove, (E)xit").ToLower();

    switch (command)
    {
        case "v":
            Announcer(" \n\nEnter listing: ");
        //ViewDirectory();//call view directory here
            break;
        case "c":
            Announcer(" \n\nEnter comment: ");
            break;
        case "s":
        {
            //we want to do a selectString method that returns length of selects here
            String select = GetString(" \n\n(1)st Selection, (2)nd Selection, (3)rd book, (E)xit").ToLower()

            switch (select)
            {
                case "1":
                    Announcer(" \n\nDisplay book info + allow for user comment entering"); 
                    break;
                case "2":
                    Announcer(" \n\nDisplay book info + allow for user comment entering");
                    break;
                case "3":
                    Announcer(" \n\nDisplay book info + allow for user comment entering");
                    break;
            }
            break;
        }
        case "e":
            isValid = false;
            break;
        default:
            Console.WriteLine("\n\nOopsy, I don't know that command! \n\n");
            break;
    }
    return isValid;
}

Answer 7

If you have a switch statement do not put anything outside the case statements, otherwise you will get that error.

switch (val)
{
    //this line should not be here
    dosomething1(); //==>error
    case "low":
        dosomething2();
        break;
    case "high":
        dosomething3();
        break;
}