Question

我制作了带有列表的书架应用程序。基本上，用户输入他们想要添加的书籍数量，然后这样做。底部方法是问题的根源（ListBooks）。我正在尝试打印列表，但它将它们打印为空白。

class Shelf
{
    public void Program()
    {
        List<string> bookTitle = new List<string>();
        List<string> bookAuthor = new List<string>();
        List<int> bookPageCount = new List<int>();
        List<int> bookWordCount = new List<int>();

        Console.WriteLine("1. Add Book.");
        Console.WriteLine("2. List Book.");
        Console.WriteLine("3. Quit.");

        int userEntry = int.Parse(Console.ReadLine());
        switch(userEntry)
        {
            case 1:
                AddBook(bookTitle, bookAuthor, bookPageCount, bookWordCount);
                break;

            case 2:
                ListBook(bookTitle, bookAuthor, bookPageCount, bookWordCount);
                break;

            case 3:
                Environment.Exit(1);
                break;
        }
    }

    public void AddBook(List<string> bookTitle, List<string> bookAuthor, List<int> bookPageCount, List<int>bookWordCount)
    {

        string title, author;
        int bookQuantity, pageCount, wordCount, userEntry;


        Console.WriteLine("Enter amount of books you would like to add.");
        bookQuantity = int.Parse(Console.ReadLine());


        for (int x = 1; x <= bookQuantity; x++)
        {
            Console.WriteLine("Enter title.");
            title = Console.ReadLine();
            bookTitle.Add(title);

            Console.WriteLine("Enter author.");
            author = Console.ReadLine();
            bookAuthor.Add(author);

            Console.WriteLine("Enter page count.");
            pageCount = int.Parse(Console.ReadLine());
            bookPageCount.Add(pageCount);

            Console.WriteLine("Enter word count.");
            wordCount = int.Parse(Console.ReadLine());
            bookWordCount.Add(wordCount);
        }


        Console.WriteLine("1. Main Menu.");
        userEntry = int.Parse(Console.ReadLine());

        switch(userEntry)
        {
            case 1:
                Program();
                break;

            default:
                Console.WriteLine("Please enter valid data.");
                Program();
                break;
        }
    }

    public void ListBook(List<string> bookTitle, List<string> bookAuthor, List<int> bookPageCount, List<int>bookWordCount)
    {

        int userEntry;

        Console.WriteLine("1. Titles.");
        Console.WriteLine("2. Authors.");

        userEntry = int.Parse(Console.ReadLine());

        switch(userEntry)
        {
            case 1:
                bookTitle.ForEach(Console.WriteLine); // Prints blank 
                break;

            case 2:
                bookAuthor.ForEach(Console.WriteLine); // Prints blank
                break;

            default:
                Console.WriteLine("Please enter valid data.");
                Program();
                break;
        }

        Console.ReadKey();
    }

}

一切似乎都在这里，所以我不知道为什么会这样做。有没有人有什么建议？提前谢谢你。

Answer 1

您应该将列表保留为类字段。目前，您将它们作为局部变量，并在每次输入Program()方法时初始化它们：

class Shelf
{
    List<string> bookTitle = new List<string>();
    List<string> bookAuthor = new List<string>();
    List<int> bookPageCount = new List<int>();
    List<int> bookWordCount = new List<int>();

    public void Program()
    {
       // removed from here
    }
}

注意：递归Program()来电是一个坏主意。这里只会使程序逻辑变得复杂，在某些时候你会以StackOverflowException结束，因为你会在递归调用中得到很深的回报。改为使用主菜单开关周围的循环。您应该从其他方法中删除Program()个调用并使用无限循环：

public void Program()
{
    List<string> bookTitle = new List<string>();
    List<string> bookAuthor = new List<string>();
    List<int> bookPageCount = new List<int>();
    List<int> bookWordCount = new List<int>();

    while (true)
    {
        Console.WriteLine("1. Add Book.");
        Console.WriteLine("2. List Book.");
        Console.WriteLine("3. Quit.");

        int userEntry = int.Parse(Console.ReadLine());
        switch (userEntry)
        {
            case 1:
                AddBook(bookTitle, bookAuthor, bookPageCount, bookWordCount);
                break;
            case 2:
                ListBook(bookTitle, bookAuthor, bookPageCount, bookWordCount);
                break;
            case 3:
                Environment.Exit(1);
                return;
        }
    }
}

如果您想进一步改进您的代码，那么创建书类，它将保存所有图书数据

public class Book
{
   public string Title { get; set; }
   public string Author { get; set; }
   public int PageCount { get; set; }
   public int WordCount { get; set; }
}

保留这些对象的单个列表，而不是四个不同的列表。

当我打印我的列表时，它们是空白的。为什么是这样？

1 个答案: