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Detailed explanation of the usage of Dictionary in C#

黄舟
Release: 2017-09-07 13:38:07
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1. To use the Dictionary collection, you need to import the C# generic namespace


 System.Collections.Generic //程序集:mscorlib
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2. Description of Dictionary

A mapping from a set of keys (Key) to a set of values ​​(Value). Each added item consists of a value and its related The key composition of the connection

Any key must be unique

The key cannot be a null reference null (Nothing in VB). If the value is a reference type, it can be a null value

Key and Value can be of any type (string, int, custom class, etc.)

3.DictionaryCommon usage: The key type is int, the value type Take string as an example

Create and initialize


##

 Dictionary<int,string> myDictionary=new Dictionary<int,string>();
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Add elements


myDictionary.Add(1,"C#");

myDictionary.Add(2,"C++");

myDictionary.Add(3,"ASP.NET");

myDictionary.Add(4,"MVC");
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Find elements by Key


if(myDictionary.ContainsKey(1))

{

  Console.WriteLine("Key:{0},Value:{1}","1", myDictionary[1]);

 }
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Traverse elements by KeyValuePair


foreach(KeyValuePair<int,string> kvp in myDictionary)

{

    Console.WriteLine("Key = {0}, Value = {1}",kvp.Key, kvp.Value);

}
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Only traverse the key Keys attribute


Dictionary<int,string>.KeyCollection keyCol = myDictionary.Keys;foreach(intkeyinkeyCol)

{

  Console.WriteLine("Key = {0}", key);

}
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Only traverse the value Valus attribute


Dictionary<int,string>.ValueCollection valueCol = myDictionary.Values;foreach(stringvalueinvalueCol)

{

   Console.WriteLine("Value = {0}", value);

}
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Remove the specified key value through the Remove method


myDictionary.Remove(1);if(myDictionary.ContainsKey(1))

{

  Console.WriteLine("Key:{0},Value:{1}","1", myDictionary[1]);

}else{

    Console.WriteLine("不存在 Key : 1"); 

 }
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4 .

Explanations of other common properties and methods:


  Comparer:          // 获取用于确定字典中的键是否相等的 IEqualityComparer。
  Count:                 // 获取包含在 Dictionary中的键/值对的数目。
  Item:                    //获取或设置与指定的键相关联的值。
  Keys:                  // 获取包含 Dictionary中的键的集合。
  Values:               // 获取包含 Dictionary中的值的集合。
  Add:                   // 将指定的键和值添加到字典中。
  Clear:                  //从 Dictionary中移除所有的键和值。
  ContainsKey:      //确定 Dictionary是否包含指定的键。
  ContainsValue:   //确定 Dictionary是否包含特定值。             
  GetEnumerator: // 返回循环访问 Dictionary的枚举数。
  GetType:           //  获取当前实例的 Type。 (从 Object 继承。)
  Remove:             //从 Dictionary中移除所指定的键的值。
  ToString:             //返回表示当前 Object的 String。 (从 Object 继承。)
  TryGetValue:      //获取与指定的键相关联的值。
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