索引器允许对象(如数组)进行索引，当您为类定义索引器时，此类的行为类似于虚拟数组，然后可以使用数组访问运算符([])访问此类的。
一维索引器具有以下语法-
element-type this[int index] {//The get accessor. get { //返回 index 指定的值 }
//The set accessor. set { //设置 index 指定的值 } }
Indexers索引
索引器的行为声明在某种程度上类似于属性，与属性类似，您可以使用get和set访问器来定义索引器。但是，属性返回或设置特定的数据成员，而索引器从对象返回或设置特定值。换句话说，它将数据分解为更小的部分，并对每个部分进行索引，获取或设置每个部分。
索引器不是使用名称定义的，而是使用this关键字定义的，该关键字引用对象。
using System;
namespace IndexerApplication {
class IndexedNames {
private string[] namelist = new string[size];
static public int size = 10;
</span><span class="kwd">public</span><span class="pln"> </span><span class="typ">IndexedNames</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln"> i </span><span class="pun"><</span><span class="pln"> size</span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++)</span><span class="pln">
namelist</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"N. A."</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">string</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">[</span><span class="kwd">int</span><span class="pln"> index</span><span class="pun">]</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">get</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">string</span><span class="pln"> tmp</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">if</span><span class="pun">(</span><span class="pln"> index </span><span class="pun">>=</span><span class="pln"> </span><span class="lit">0</span><span class="pln"> </span><span class="pun">&&</span><span class="pln"> index </span><span class="pun"><=</span><span class="pln"> size</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
tmp </span><span class="pun">=</span><span class="pln"> namelist</span><span class="pun">[</span><span class="pln">index</span><span class="pun">];</span><span class="pln">
</span><span class="pun">}</span><span class="pln"> </span><span class="kwd">else</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
tmp </span><span class="pun">=</span><span class="pln"> </span><span class="str">""</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">return</span><span class="pln"> </span><span class="pun">(</span><span class="pln"> tmp </span><span class="pun">);</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">set</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">if</span><span class="pun">(</span><span class="pln"> index </span><span class="pun">>=</span><span class="pln"> </span><span class="lit">0</span><span class="pln"> </span><span class="pun">&&</span><span class="pln"> index </span><span class="pun"><=</span><span class="pln"> size</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
namelist</span><span class="pun">[</span><span class="pln">index</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">value</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="typ">Main</span><span class="pun">(</span><span class="kwd">string</span><span class="pun">[]</span><span class="pln"> args</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="typ">IndexedNames</span><span class="pln"> names </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">IndexedNames</span><span class="pun">();</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Zara"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Riz"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">2</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Nuha"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">3</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Asif"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">4</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Davinder"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">5</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Sunil"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">6</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Rubic"</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln"> i </span><span class="pun"><</span><span class="pln"> </span><span class="typ">IndexedNames</span><span class="pun">.</span><span class="pln">size</span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++</span><span class="pln"> </span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="pln">names</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]);</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="typ">Console</span><span class="pun">.</span><span class="typ">ReadKey</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
}
}
编译并执行上述代码时，将生成以下输出-
Zara Riz Nuha Asif Davinder Sunil Rubic N. A. N. A. N. A.
Indexers索引重载
索引器也可以用多个参数声明，每个参数可以是不同的类型，索引不必是整数，C#允许索引为其他类型，如字符串。
下面的示例演示重载索引器-
using System;
namespace IndexerApplication {
class IndexedNames {
private string[] namelist = new string[size];
static public int size = 10;
</span><span class="kwd">public</span><span class="pln"> </span><span class="typ">IndexedNames</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln"> i </span><span class="pun"><</span><span class="pln"> size</span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
namelist</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"N. A."</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">string</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">[</span><span class="kwd">int</span><span class="pln"> index</span><span class="pun">]</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">get</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">string</span><span class="pln"> tmp</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">if</span><span class="pun">(</span><span class="pln"> index </span><span class="pun">>=</span><span class="pln"> </span><span class="lit">0</span><span class="pln"> </span><span class="pun">&&</span><span class="pln"> index </span><span class="pun"><=</span><span class="pln"> size</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
tmp </span><span class="pun">=</span><span class="pln"> namelist</span><span class="pun">[</span><span class="pln">index</span><span class="pun">];</span><span class="pln">
</span><span class="pun">}</span><span class="pln"> </span><span class="kwd">else</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
tmp </span><span class="pun">=</span><span class="pln"> </span><span class="str">""</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">return</span><span class="pln"> </span><span class="pun">(</span><span class="pln"> tmp </span><span class="pun">);</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">set</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">if</span><span class="pun">(</span><span class="pln"> index </span><span class="pun">>=</span><span class="pln"> </span><span class="lit">0</span><span class="pln"> </span><span class="pun">&&</span><span class="pln"> index </span><span class="pun"><=</span><span class="pln"> size</span><span class="pun">-</span><span class="lit">1</span><span class="pln"> </span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
namelist</span><span class="pun">[</span><span class="pln">index</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">value</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">int</span><span class="pln"> </span><span class="kwd">this</span><span class="pun">[</span><span class="kwd">string</span><span class="pln"> name</span><span class="pun">]</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">get</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">int</span><span class="pln"> index </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln">
</span><span class="kwd">while</span><span class="pun">(</span><span class="pln">index </span><span class="pun"><</span><span class="pln"> size</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">if</span><span class="pln"> </span><span class="pun">(</span><span class="pln">namelist</span><span class="pun">[</span><span class="pln">index</span><span class="pun">]</span><span class="pln"> </span><span class="pun">==</span><span class="pln"> name</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="kwd">return</span><span class="pln"> index</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
index</span><span class="pun">++;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">return</span><span class="pln"> index</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> </span><span class="typ">Main</span><span class="pun">(</span><span class="kwd">string</span><span class="pun">[]</span><span class="pln"> args</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="typ">IndexedNames</span><span class="pln"> names </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">IndexedNames</span><span class="pun">();</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Zara"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Riz"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">2</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Nuha"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">3</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Asif"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">4</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Davinder"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">5</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Sunil"</span><span class="pun">;</span><span class="pln">
names</span><span class="pun">[</span><span class="lit">6</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="str">"Rubic"</span><span class="pun">;</span><span class="pln">
</span><span class="com">//using the first indexer with int parameter</span><span class="pln">
</span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln"> i </span><span class="pun"><</span><span class="pln"> </span><span class="typ">IndexedNames</span><span class="pun">.</span><span class="pln">size</span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
</span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="pln">names</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]);</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
</span><span class="com">//using the second indexer with the string parameter</span><span class="pln">
</span><span class="typ">Console</span><span class="pun">.</span><span class="typ">WriteLine</span><span class="pun">(</span><span class="pln">names</span><span class="pun">[</span><span class="str">"Nuha"</span><span class="pun">]);</span><span class="pln">
</span><span class="typ">Console</span><span class="pun">.</span><span class="typ">ReadKey</span><span class="pun">();</span><span class="pln">
</span><span class="pun">}</span><span class="pln">
}
}
编译并执行上述代码时，将生成以下输出-
Zara Riz Nuha Asif Davinder Sunil Rubic N. A. N. A. N. A. 2
