本教程展示如何實(shí)現(xiàn)使用索引屬性的類。索引屬性使您可以使用表示類似于數(shù)組的若干種不同事物的集合的類。學(xué)習(xí)本教程以前應(yīng)完成索引器教程。
示例文件
請(qǐng)參見(jiàn)“索引屬性”示例以下載和生成本教程中討論的示例文件。
教程
假定您要編寫(xiě)一個(gè) Document 類，該類封裝非常長(zhǎng)的文本章節(jié)。為能夠方便地實(shí)現(xiàn)各種操作（如檢查拼寫(xiě)），您可能希望以單詞（以及字符）的虛擬數(shù)組形式查看文檔。
下面的示例展示實(shí)現(xiàn)這種類的技術(shù)。對(duì)于每個(gè)“索引屬性”，您定義一個(gè)嵌套類，該類包含對(duì)主類實(shí)例的反向引用。主類上的 readonly 字段提供對(duì)嵌套類（定義每個(gè)虛擬數(shù)組）的實(shí)例的訪問(wèn)。每個(gè)嵌套類定義一個(gè)索引器以及其他類似集合的方法（例如 Count 屬性）。下面的示例針對(duì)“Words”和“Characters”展示這一點(diǎn)。
注意???請(qǐng)慎重使用該技術(shù)！僅在使用數(shù)組索引操作提供的抽象化能明確闡明使用您的類的代碼，并且索引器同時(shí)具有“獲取”(Get) 和“設(shè)置”(Set) 訪問(wèn)器時(shí)，才使用該模式。
示例
本示例中定義了 Document 類。使用 Words 和 Characters 這兩個(gè)索引屬性在 Document 對(duì)象上執(zhí)行某些文本操作。
// indexedproperty.cs
using System;
public class Document
{
// Type allowing the document to be viewed like an array of words:
public class WordCollection
{
readonly Document document; // The containing document
internal WordCollection(Document d)
{
document = d;
}
// Helper function -- search character array "text", starting at
// character "begin", for word number "wordCount." Returns false
// if there are less than wordCount words. Sets "start" and
// length" to the position and length of the word within text:
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;
}
// Indexer to get and set words of the containing document:
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))
{
// Replace the word at start/length with the
// string "value":
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();
}
}
// Get the count of words in the containing document:
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;
}
}
}
// Type allowing the document to be viewed like an "array"
// of characters:
public class CharacterCollection
{
readonly Document document; // The containing document
internal CharacterCollection(Document d)
{
document = d;
}
// Indexer to get and set characters in the containing document:
public char this[int index]
{
get
{
return document.TextArray[index];
}
set
{
document.TextArray[index] = value;
}
}
// Get the count of characters in the containing document:
public int Count
{
get
{
return document.TextArray.Length;
}
}
}
// Because the types of the fields have indexers,
// these fields appear as "indexed properties":
public readonly WordCollection Words;
public readonly CharacterCollection Characters;
private char[] TextArray; // The text of the document.
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?"
);
// Change word "peter" to "penelope":
for (int i = 0; i < d.Words.Count; ++i)
{
if (d.Words[i] == "peter")
d.Words[i] = "penelope";
}
// Change character "p" to "P"
for (int i = 0; i < d.Characters.Count; ++i)
{
if (d.Characters[i] == 'p')
d.Characters[i] = 'P';
}
Console.WriteLine(d.Text);
}
}
輸出
PeneloPe PiPer Picked a Peck of Pickled PePPers. How many Pickled PePPers did PeneloPe PiPer Pick?