c# 索引器（Dictionary赋值取值的方式）
1 什么是索引器？
索引器提供了一种访问类或者结构的方法，即允许按照与数组相同的方式对类、结构或接口进行索引。
例如：Dictionary（词典类）的赋值取值方式。
2 数字索引器
2.1 定义一个索引器类
public class University
{
private const int MAX = 10;
private string[] names = new string[MAX];
//索引器
public string this[int index]
{
get
{
if(index >= 0 && index < MAX)
{
return names[index];
}
return null;
}
set
{
if (index >= 0 && index < MAX)
{
names[index] = value;
}
}
}
}
2.2 使用这个索引器类
University u = new University();
u[0] = "测试大学0";
u[1] = "测试大学1";
u[2] = "测试大学2";
System.Console.WriteLine(u[0]);
System.Console.WriteLine(u[1]);
System.Console.WriteLine(u[2]);
2.3 话白
是不是很像Dictionary（词典类）的赋值取值方式了？但这只能用数字来索引；
3 字符串索引器
3.1 定义一个索引器类
public class MySimpleDictionary
{
private List<KeyValueEntity> keyValueEntitys = new List<KeyValueEntity>();
//索引器
public object this[string key]
{
get
{
foreach(KeyValueEntity keyValueEntity in keyValueEntitys)
{
if (keyValueEntity.key == key)
{
return keyValueEntity.value;
}
}
return null;
}
set
{
foreach (KeyValueEntity keyValueEntity in keyValueEntitys)
{
if (keyValueEntity.key == key)
{
keyValueEntity.value = value;
//短路
return;
}
}
KeyValueEntity newKeyValueEntity = new KeyValueEntity();
newKeyValueEntity.key = key;
newKeyValueEntity.value = value;
keyValueEntitys.Add(newKeyValueEntity);
}
}
}
public class KeyValueEntity
{
public string key { set; get; }
public object value { set; get; }
}
3.2 使用这个索引器类
MySimpleDictionary mydic = new MySimpleDictionary();
mydic["testKey0"] = "testValue0";
mydic["testKey1"] = "testValue1";
mydic["testKey2"] = "testValue2";
System.Console.WriteLine(mydic["testKey0"]);
System.Console.WriteLine(mydic["testKey1"]);
System.Console.WriteLine(mydic["testKey2"]);
3.3 话白
是不是更像Dictionary（词典类）的赋值取值方式了？但这只能用字符串来索引；
接下来，我们在此基础上改造一个泛型的；
4 泛型索引器
4.1 定义一个索引器类
public class MySimpleDictionary<T, U>
{
private List<KeyValueEntity<T, U>> keyValueEntitys = new List<KeyValueEntity<T, U>>();
//索引器
public U this[T key]
{
get
{
foreach (KeyValueEntity<T, U> keyValueEntity in keyValueEntitys)
{
if (keyValueEntity.key.Equals(key))
{
return keyValueEntity.value;
}
}
return default(U);
}
set
{
foreach (KeyValueEntity<T, U> keyValueEntity in keyValueEntitys)
{
if (keyValueEntity.key.Equals(key))
{
keyValueEntity.value = value;
//短路
return;
}
}
KeyValueEntity<T, U> newKeyValueEntity = new KeyValueEntity<T, U>();
newKeyValueEntity.key = key;
newKeyValueEntity.value = value;
keyValueEntitys.Add(newKeyValueEntity);
}
}
}
public class KeyValueEntity<T, U>
{
public T key { set; get; }
public U value { set; get; }
}
4.2 使用这个索引器类
MySimpleDictionary<string, string> dic = new MySimpleDictionary<string, string>();
dic["testKey0"] = "testValue0";
dic["testKey1"] = "testValue1";
dic["testKey2"] = "testValue2";
System.Console.WriteLine(dic["testKey0"]);
System.Console.WriteLine(dic["testKey1"]);
System.Console.WriteLine(dic["testKey2"]);
4.3 白话
到这里为止，我写的这个【简化版的Dictionary】跟【.net框架的Dictionary】相比还有一点较大的不同，如下：
1）数据结构算法不同
我写的词典类，是简单的键值对列表；
框架的词典类，是动态扩展的数组+hash冲突解决算法，有兴趣的同学去看源码，毕竟我这篇博客主要讲的是索引器；
5 组合索引器
5.1 定义一个索引器类
public class MySimpleDictionary
{
private List<GroupKeyValueEntity> keyValueEntitys = new List<GroupKeyValueEntity>();
//索引器
public object this[string group, string key]
{
get
{
foreach (GroupKeyValueEntity keyValueEntity in keyValueEntitys)
{
if (keyValueEntity.group == group && keyValueEntity.key == key)
{
return keyValueEntity.value;
}
}
return null;
}
set
{
foreach (GroupKeyValueEntity keyValueEntity in keyValueEntitys)
{
if (keyValueEntity.group == group && keyValueEntity.key == key)
{
keyValueEntity.value = value;
//短路
return;
}
}
GroupKeyValueEntity newKeyValueEntity = new GroupKeyValueEntity();
newKeyValueEntity.group = group;
newKeyValueEntity.key = key;
newKeyValueEntity.value = value;
keyValueEntitys.Add(newKeyValueEntity);
}
}
}
public class GroupKeyValueEntity
{
public string group { set; get; }
public string key { set; get; }
public object value { set; get; }
}
5.2 使用这个索引器类
MySimpleDictionary dic = new MySimpleDictionary();
dic["group0", "key0"] = "value0";
dic["group0", "key1"] = "value1";
dic["group0", "key2"] = "value2";
dic["group1", "key0"] = "value3";
dic["group1", "key1"] = "value4";
dic["group1", "key2"] = "value5";
System.Console.WriteLine(dic["group0", "key0"]);
System.Console.WriteLine(dic["group0", "key1"]);
System.Console.WriteLine(dic["group0", "key2"]);
System.Console.WriteLine(dic["group1", "key0"]);
System.Console.WriteLine(dic["group1", "key1"]);
System.Console.WriteLine(dic["group1", "key2"]);
5.3 白话
组合索引器不常用，对应的泛型就不在这里赘述了，有兴趣的同学不妨自己改造一下，毕竟泛型的用法还是很简单滴。。。
