ex-09-09

Programming Csharp Source Code(代码) Programming Csharp Source Code

// Example 09-09: Using a simple indexer

namespace Programming_CSharp
{
   using System;
  
   // a simplified ListBox control
   public class ListBoxTest
   {
      // initialize the list box with strings
      public ListBoxTest(params string[] initialStrings)
      {
         // allocate space for the strings
         strings = new String[256]; 

         // copy the strings passed in to the constructor
         foreach (string s in initialStrings)
         {
            strings[ctr++] = s;
         }
      }

      // add a single string to the end of the list box
      public void Add(string theString)
      {
         if (ctr >= strings.Length)
         {
            // handle bad index
         }
         else
            strings[ctr++] = theString;
      }

      // allow array-like access
      public string this[int index]
      {
         get
         {
            if (index < 0 || index >= strings.Length)
            {
               // handle bad index
            }
            return strings[index];
         }
         set
         {
            // add only through the add method
            if (index >= ctr )
            {
               // handle error
            }
            else
               strings[index] = value;
         }
      }
   
      // publish how many strings you hold
      public int GetNumEntries()
      {
         return ctr;
      }

      private string[] strings;
      private int ctr = 0;
   }
    
   public class Tester
   {
      static void Main()
      {
         // create a new list box and initialize
         ListBoxTest lbt = 
            new ListBoxTest("Hello", "World");

         // add a few strings
         lbt.Add("Who");
         lbt.Add("Is");
         lbt.Add("John");
         lbt.Add("Galt");

         // test the access
         string subst = "Universe";
         lbt[1] = subst;

         // access all the strings
         for (int i = 0;i<lbt.GetNumEntries();i++)
         {
            Console.WriteLine("lbt[{0}]: {1}",i,lbt[i]);
         }
      }
   }
}