就可以了，另外告诉你dictionary的时间效率是1，是一个很效率很高的数据结构。
既然时间效率是1，那么我们寻址的时候就是直接寻址，也不需要去遍历dictionary，这就是为什么键必须唯一，不能重复的原因，如果重复了就不可能再是直接寻址的方式了。
var dic = new Dictionary<string, int>() { {"a",1}, {"b",2}, {"c",3}, {"d",1} }foreach (var item in dic) { if (item.Value == 1) { Console.WriteLine(item.Key)} }
1.最直白的循环遍历方法，可以分为遍历key--value键值对以及所有的key两种表现形式
2.用Linq的方式去查询（当然了这里要添加对应的命名空间 using System.Linq）
如下为一个十分简单的代码示例：
private void GetDicKeyByValue()
{
Dictionary<string, string>dic = new Dictionary<string, string>()
dic.Add("1", "1")
dic.Add("2", "2")
dic.Add("3", "2")
//foreach KeyValuePair traversing
foreach (KeyValuePair<string, string>kvp in dic)
{
if (kvp.Value.Equals("2"))
{
//...... kvp.Key
}
}
//foreach dic.Keys
foreach (string key in dic.Keys)
{
if (dic[key].Equals("2"))
{
//...... key
}
}
//Linq
var keys = dic.Where(q =>q.Value == "2").Select(q =>q.Key) //get all keys
List<string>keyList = (from q in dic
where q.Value == "2"
select q.Key).ToList<string>()//get all keys
var firstKey = dic.FirstOrDefault(q =>q.Value == "2").Key //get first key
}
C# Dictionary用法总结
1、用法1： 常规用
增加键值对之前需要判断是否存在该键，如果已经存在该键而且不判断，将抛出异常。所以这样每次都要进行判断，很麻烦，在备注里使用了一个扩展方法
public static void DicSample1(){
Dictionary<String, String> pList = new Dictionary<String, String>()
try
{
if (pList.ContainsKey("Item1") == false)
{
pList.Add("Item1", "ZheJiang")
}
if (pList.ContainsKey("Item2")== false)
{
pList.Add("Item2", "ShangHai")
}
else
{
pList["Item2"] = "ShangHai"
}
if (pList.ContainsKey("Item3") == false)
{
pList.Add("Item3", "BeiJiang")
}
}
catch (System.Exception e)
{
Console.WriteLine("Error: {0}", e.Message)
}
//判断是否存在相应的key并显示
if (pList.ContainsKey("Item1"))
{
Console.WriteLine("Output: " + pList["Item1"])
}
//遍历Key
foreach (var key in pList.Keys)
{
Console.WriteLine("Output Key: {0}", key)
}
//遍历Value
foreach (String value in pList.Values)
{
Console.WriteLine("Output Value: {0}", value)
}
//遍历Key和Value
foreach (var dic in pList)
{
Console.WriteLine("Output Key : {0}, Value : {1} ", dic.Key, dic.Value)
}
}
2、用法2：Dictionary的Value为一个数组
/// <summary>/// Dictionary的Value为一个数组
/// </summary>
public static void DicSample2()
{
Dictionary<String, String[]> dic = new Dictionary<String, String[]>()
String[] ZheJiang = { "Huzhou", "HangZhou", "TaiZhou" }
String[] ShangHai = { "Budong", "Buxi" }
dic.Add("ZJ", ZheJiang)
dic.Add("SH", ShangHai)
Console.WriteLine("Output :" + dic["ZJ"][0])
}
3、用法3： Dictionary的Value为一个类
//Dictionary的Value为一个类public static void DicSample3()
{
Dictionary<String, Student> stuList = new Dictionary<String, Student>()
Student stu = null
for (int i = 0 i < 3 i++ )
{
stu = new Student()
stu.Name = i.ToString()
stu.Name = "StuName" + i.ToString()
stuList.Add(i.ToString(), stu)
}
foreach (var student in stuList)
{
Console.WriteLine("Output : Key {0}, Num : {1}, Name {2}", student.Key, student.Value.Name, student.Value.Name)
}
}
Student类：
public class Student
{
public String Num { get set }
public String Name { get set }
}
4 备注：Dictionary的扩展方法使用
/// <summary>/// Dictionary的扩展方法使用
/// </summary>
public static void DicSample4()
{
//1)普通调用
Dictionary<int, String> dict = new Dictionary<int, String>()
DictionaryExtensionMethodClass.TryAdd(dict, 1, "ZhangSan")
DictionaryExtensionMethodClass.TryAdd(dict, 2, "WangWu")
DictionaryExtensionMethodClass.AddOrPeplace(dict, 3, "WangWu")
DictionaryExtensionMethodClass.AddOrPeplace(dict, 3, "ZhangWu")
DictionaryExtensionMethodClass.TryAdd(dict, 2, "LiSi")
//2)TryAdd 和 AddOrReplace 这两个方法具有较强自我描述能力，用起来很省心，而且也简单：
dict.AddOrPeplace(20, "Orange")
dict.TryAdd(21, "Banana")
dict.TryAdd(22, "apple")
//3)像Linq或jQuery一样连起来写
dict.TryAdd(10, "Bob")
.TryAdd(11, "Tom")
.AddOrPeplace(12, "Jom")
//4) 获取值
String F = "Ba"
dict.TryGetValue(31, out F)
Console.WriteLine("F : {0}",F)
foreach (var dic in dict)
{
Console.WriteLine("Output : Key : {0}, Value : {1}", dic.Key, dic.Value)
}
//5)下面是使用GetValue获取值
var v1 = dict.GetValue(111,null)
var v2 = dict.GetValue(10,"abc")
//6)批量添加
var dict1 = new Dictionary<int,int>()
dict1.AddOrPeplace(3, 3)
dict1.AddOrPeplace(5, 5)
var dict2 = new Dictionary<int, int>()
dict2.AddOrPeplace(1, 1)
dict2.AddOrPeplace(4, 4)
dict2.AddRange(dict1, false)
}
扩展方法所在的类
public static class DictionaryExtensionMethodClass
{
/// <summary>
/// 尝试将键和值添加到字典中：如果不存在，才添加；存在，不添加也不抛导常
/// </summary>
public static Dictionary<TKey, TValue> TryAdd<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue value)
{
if (dict.ContainsKey(key) == false)
dict.Add(key, value)
return dict
}
/// <summary>
/// 将键和值添加或替换到字典中：如果不存在，则添加；存在，则替换
/// </summary>
public static Dictionary<TKey, TValue> AddOrPeplace<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue value)
{
dict[key] = value
return dict
}
/// <summary>
/// 获取与指定的键相关联的值，如果没有则返回输入的默认值
/// </summary>
public static TValue GetValue<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, TValue defaultValue)
{
return dict.ContainsKey(key)?dict[key] : defaultValue
}
/// <summary>
/// 向字典中批量添加键值对
/// </summary>
/// <param name="replaceExisted">如果已存在，是否替换</param>
public static Dictionary<TKey, TValue> AddRange<TKey, TValue>(this Dictionary<TKey, TValue> dict, IEnumerable<KeyValuePair<TKey, TValue>> values, bool replaceExisted)
{
foreach (var item in values)
{
if (dict.ContainsKey(item.Key) == false || replaceExisted)
dict[item.Key] = item.Value
}
return dict
}
}
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