命名空间????? [英] Namespaces?????

问题描述

请考虑下面的代码来自MSDN。

为什么命名空间中的using语句？ 

问候

Manoj

 //一组用于处理书店的类：
 namespace Bookstore 
 { 
使用System.Collections; 
 
 //描述书籍清单中的书籍：
 public struct Book 
 {
 public string Title; //这本书的标题。 
 public string作者; //本书的作者。 
公共小数价格; //这本书的价格。 
 public bool平装本; //是平装本吗？ 
 
 public Book（字符串标题，字符串作者，十进制价格，bool paperBack）
 {
 Title = title; 
作者=作者; 
价格=价格; 
平装书= paperBack; 
} 
} 
 
 //声明处理书籍的委托类型：
 public delegate void ProcessBookDelegate（Book book）; 
 
 //维护图书数据库。 
公共类BookDB 
 {
 //数据库中所有书籍的列表：
 ArrayList list = new ArrayList（）; 
 
 //向数据库添加一本书：
 public void AddBook（字符串标题，字符串作者，十进制价格，bool paperBack）
 {
 list.Add（新书（标题，作者，价格，paperBack））; 
} 
 
 //在每本平装书上调用传入的委托来处理它：
 public void ProcessPaperbackBooks（ProcessBookDelegate processBook）
 {
 foreach （列表中的b）
 {
 if（b.Paperback）
 //调用委托：
 processBook（b）; 
} 
} 
} 
} 
 
 
 //使用Bookstore类：
命名空间BookTestClient 
 {使用书店
; 
 
 //账簿总价和平均价格：
 class PriceTotaller 
 {
 int countBooks = 0; 
十进制priceBooks = 0.0m; 
 
 internal void AddBookToTotal（Book book）
 {
 countBooks + = 1; 
 priceBooks + = book.Price; 
} 
 
内部小数AveragePrice（）
 {
 return priceBooks / countBooks; 
} 
} 
 
 //测试图书数据库的类：
 class TestBookDB 
 {
 //打印书的标题。 
 static void PrintTitle（Book b）
 {
 System.Console.WriteLine（" {0}"，b.Title）; 
} 
 
 //执行从这里开始。 
 static void Main（）
 {
 BookDB bookDB = new BookDB（）; 
 
 //使用一些书籍初始化数据库：
 AddBooks（bookDB）; 
 
 //打印所有平装书的标题：
 System.Console.WriteLine（&"Paperback Book Titles："）; 
 
 //创建一个与静态
 //方法相关联的新委托对象Test.PrintTitle：
 bookDB.ProcessPaperbackBooks（PrintTitle）; 
 
 //使用
获得平装书的平均价格//一个PriceTotaller对象：
 PriceTotaller totaller = new PriceTotaller（）; 
 
 //在对象totaller上创建一个与非静态
 //方法AddBookToTotal相关联的新委托对象：
 bookDB.ProcessPaperbackBooks（totaller.AddBookToTotal）; 
 
 System.Console.WriteLine（" Average Paperback Book Price：$ {0：＃。##}"，
 totaller.AveragePrice（））; 
} 
 
 //使用一些测试书初始化book数据库：
 static void AddBooks（BookDB bookDB）
 {
 bookDB.AddBook（" C Programming Language"，"Brian W. Kernighan and Dennis M. Ritchie"，19.95m，true）; 
 bookDB.AddBook（" The Unicode Standard 2.0"，The Unicode Consortium"，39.95m，true）; 
 bookDB.AddBook（" The MS-DOS Encyclopedia"，" Ray Duncan"，129.95m，false）; 
 bookDB.AddBook（" Dogbert's Clues for the Clueless"，" Scott Adams"，12.00m，true）; 
} 
} 
} 
 / *输出：
平装书标题：
 C编程语言
 Unicode标准2.0 
 Dogbert's Cluees for the Clueless 
平均平装书价格：$ 23.97 
 * / 
 

解决方案

我们也是故意使用的。  阅读此博客文章，其中说明何时使用
在命名空间内部或外部使用。

https://blogs.msdn.microsoft.com/ericlippert/2007/06/25/inside-or-outside/

Please consider the code below it is from MSDN.

Why is the using statement within the namespace? 

regards

Manoj

// A set of classes for handling a bookstore:
namespace Bookstore
{
    using System.Collections;

    // Describes a book in the book list:
    public struct Book
    {
        public string Title;        // Title of the book.
        public string Author;       // Author of the book.
        public decimal Price;       // Price of the book.
        public bool Paperback;      // Is it paperback?

        public Book(string title, string author, decimal price, bool paperBack)
        {
            Title = title;
            Author = author;
            Price = price;
            Paperback = paperBack;
        }
    }

    // Declare a delegate type for processing a book:
    public delegate void ProcessBookDelegate(Book book);

    // Maintains a book database.
    public class BookDB
    {
        // List of all books in the database:
        ArrayList list = new ArrayList();

        // Add a book to the database:
        public void AddBook(string title, string author, decimal price, bool paperBack)
        {
            list.Add(new Book(title, author, price, paperBack));
        }

        // Call a passed-in delegate on each paperback book to process it: 
        public void ProcessPaperbackBooks(ProcessBookDelegate processBook)
        {
            foreach (Book b in list)
            {
                if (b.Paperback)
                    // Calling the delegate:
                    processBook(b);
            }
        }
    }
}


// Using the Bookstore classes:
namespace BookTestClient
{
    using Bookstore;

    // Class to total and average prices of books:
    class PriceTotaller
    {
        int countBooks = 0;
        decimal priceBooks = 0.0m;

        internal void AddBookToTotal(Book book)
        {
            countBooks += 1;
            priceBooks += book.Price;
        }

        internal decimal AveragePrice()
        {
            return priceBooks / countBooks;
        }
    }

    // Class to test the book database:
    class TestBookDB
    {
        // Print the title of the book.
        static void PrintTitle(Book b)
        {
            System.Console.WriteLine("   {0}", b.Title);
        }

        // Execution starts here.
        static void Main()
        {
            BookDB bookDB = new BookDB();

            // Initialize the database with some books:
            AddBooks(bookDB);

            // Print all the titles of paperbacks:
            System.Console.WriteLine("Paperback Book Titles:");

            // Create a new delegate object associated with the static 
            // method Test.PrintTitle:
            bookDB.ProcessPaperbackBooks(PrintTitle);

            // Get the average price of a paperback by using
            // a PriceTotaller object:
            PriceTotaller totaller = new PriceTotaller();

            // Create a new delegate object associated with the nonstatic 
            // method AddBookToTotal on the object totaller:
            bookDB.ProcessPaperbackBooks(totaller.AddBookToTotal);

            System.Console.WriteLine("Average Paperback Book Price: ${0:#.##}",
                    totaller.AveragePrice());
        }

        // Initialize the book database with some test books:
        static void AddBooks(BookDB bookDB)
        {
            bookDB.AddBook("The C Programming Language", "Brian W. Kernighan and Dennis M. Ritchie", 19.95m, true);
            bookDB.AddBook("The Unicode Standard 2.0", "The Unicode Consortium", 39.95m, true);
            bookDB.AddBook("The MS-DOS Encyclopedia", "Ray Duncan", 129.95m, false);
            bookDB.AddBook("Dogbert's Clues for the Clueless", "Scott Adams", 12.00m, true);
        }
    }
}
/* Output:
Paperback Book Titles:
   The C Programming Language
   The Unicode Standard 2.0
   Dogbert's Clues for the Clueless
Average Paperback Book Price: $23.97
*/

解决方案

We use likewise on purpose. Read this blog post which explains when to use Using inside or outside namespace.

https://blogs.msdn.microsoft.com/ericlippert/2007/06/25/inside-or-outside/

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