C#索引属性用法实例分析

// indexedproperty.csusing System;public class Document{  // 以下类型允许文档的查看方式与字的数组一样：  public class WordCollection  {    readonly Document document; // 包含文档    internal WordCollection(Document d)    {      document = d;    }    // Helper 函数 -- 从字符“begin”开始在字符数组“text”中搜索    // 字数“wordCount”。如果字数小于 wordCount，    // 则返回 false。将“start”和    // “length”设置为单词在文本中的位置和长度:    private bool GetWord(char[] text, int begin, int wordCount, out int start, out int length)     {       int end = text.Length;      int count = 0;      int inWord = -1;      start = length = 0;       for (int i = begin; i <= end; ++i)       {        bool isLetter = i < end && Char.IsLetterOrDigit(text[i]);        if (inWord >= 0)         {          if (!isLetter)           {            if (count++ == wordCount)             {              start = inWord;              length = i - inWord;              return true;            }            inWord = -1;          }        }        else         {          if (isLetter)            inWord = i;        }      }      return false;    }    // 获取和设置包含文档中的字的索引器：    public string this[int index]     {      get       {         int start, length;        if (GetWord(document.TextArray, 0, index, out start, out length))          return new string(document.TextArray, start, length);        else          throw new IndexOutOfRangeException();      }      set       {        int start, length;        if (GetWord(document.TextArray, 0, index, out start, out length))         {          // 用字符串“value”替换位于 start/length 处的          // 字：          if (length == value.Length)           {            Array.Copy(value.ToCharArray(), 0, document.TextArray, start, length);          }          else           {            char[] newText =               new char[document.TextArray.Length + value.Length - length];            Array.Copy(document.TextArray, 0, newText, 0, start);            Array.Copy(value.ToCharArray(), 0, newText, start, value.Length);            Array.Copy(document.TextArray, start + length, newText, start + value.Length, document.TextArray.Length - start - length);            document.TextArray = newText;          }        }                  else          throw new IndexOutOfRangeException();      }    }    // 获取包含文档中字的计数：    public int Count     {      get       {         int count = 0, start = 0, length = 0;        while (GetWord(document.TextArray, start + length, 0, out start, out length))          ++count;        return count;       }    }  }  // 以下类型允许文档的查看方式像字符的“数组”  // 一样：  public class CharacterCollection  {    readonly Document document; // 包含文档    internal CharacterCollection(Document d)    {     document = d;     }    // 获取和设置包含文档中的字符的索引器：    public char this[int index]     {      get       {         return document.TextArray[index];       }      set       {         document.TextArray[index] = value;       }    }    // 获取包含文档中字符的计数：    public int Count     {      get       {         return document.TextArray.Length;       }    }  }  // 由于字段的类型具有索引器，  // 因此这些字段显示为“索引属性”：  public WordCollection Words;  public CharacterCollection Characters;  private char[] TextArray; // 文档的文本。  public Document(string initialText)  {    TextArray = initialText.ToCharArray();    Words = new WordCollection(this);    Characters = new CharacterCollection(this);  }  public string Text   {    get     {       return new string(TextArray);     }  }}class Test{  static void Main()  {    Document d = new Document(      "peter piper picked a peck of pickled peppers. How many pickled peppers did peter piper pick?"    );    // 将字“peter”更改为“penelope”：    for (int i = 0; i < d.Words.Count; ++i)     {      if (d.Words[i] == "peter")         d.Words[i] = "penelope";    }    // 将字符“p”更改为“P”    for (int i = 0; i < d.Characters.Count; ++i)     {      if (d.Characters[i] == 'p')        d.Characters[i] = 'P';    }    Console.WriteLine(d.Text);  }}