C # Generic collection of dictionary<k, v> usage tips

2. 1. To use the dictionary collection, you need to import the C # generic namespace
4. System.Collections.Generic (assembly: mscorlib)
6. 2. Description
8. 1), a mapping from a set of keys (key) to a set of values (value), each of which is made up of a value and its associated key
10. 2), any key must be unique
12. 3), the key cannot be null reference null (Nothing in VB), if the value is a reference type, it can be a null value
14. 4), key and value can be of any type (string,Int,custom class, etc.)
16. 3. Create and initialize
20. dictionary<int, string> mydictionary = new dictionary<int, string> ();
24. 4. Adding elements
28. Mydictionary.add ("C #", 0);
30. Mydictionary.add ("C + +", 1);
32. Mydictionary.add ("C", 2);
34. Mydictionary.add ("VB", 2);
38. 5. Find element by Key
42. 　　if (Mydictionary.containskey ("C #"))
44. {
46. Console.WriteLine ("Key:{0},value:{1}", "C #", mydictionary["C #"]);
48. }
52. 6. Traverse element by KeyValuePair
56. 　　foreach (keyvaluepair<string, int> kvp in mydictionary)
58. {
60. Console.WriteLine ("Key = {0}, Value = {1}", kvp. Key, kvp. Value);
62. }
66. 7. Traverse key by Keys property only
70. dictionary<string, int>. KeyCollection keycol = Mydictionary.keys;
72. 　　foreach (string key in keycol/*string key in mydictionary.keys*/)
74. {
76. Console.WriteLine ("key = {0}", key);
78. }
82. 8. Traverse only the value by Valus property
86. dictionary<string, int>. ValueCollection valuecol = mydictionary.values;
88. 　　foreach (int value in valuecol)
90. {
92. Console.WriteLine ("value = {0}", value);
94. }
98. 9. Removing the specified key value by the Remove method
102. Mydictionary.remove ("C #");
104. 　　if (Mydictionary.containskey ("C #"))
106. {
108. Console.WriteLine ("Key:{0},value:{1}", "C #", mydictionary["C #"]);
110. }
112. 　　Else
114. {
116. Console.WriteLine ("non-existent key:c#");
118. }
122. In the System.Collections.Generic namespace, the generic set corresponding to the ArrayList is List<t>, and the generic collection corresponding to the Hashtable is dictionary<k,v> It stores data in a way that is similar to a hash table, holds elements by key/value, has all the characteristics of generics, checks type constraints at compile time, and does not require type conversions when reading.
126. Phone Book storage example, using dictionary<k,v> to store the telephone information, the code is as follows:
132. dictionary<string,telnote> ht=new dictionary<string,telnote> ();
136. In the dictionary<k,v> declaration,string in "< String,telnote>" represents the type of key in the collection, Telnote represents the type of value, and the definition dictionary The methods in the <K,V> generic collection are as follows:
142. dictionary<k,v> students=New dictionary<k,v> ();
146. where "K" is a placeholder, specifically defined with the storage key "key" of the data type instead, "V" is also a placeholder, with the value of the element "value" of the data type instead, so that when the collection is defined, the data type of the key and value of the stored element is declared, guaranteeing the type of security.
148. The elements in dictionary<k,v> are similar to Hashtable, adding elements, getting elements, deleting elements, and iterating through the elements of the collection basically the same way.
152. The difference between dictionary<k,v> and Hashtable
154. Dictionary<k,v> and Hashtable are the same: add elements, delete elements, and access values by key in the same way.
156. Different points of dictionary<k,v> and Hashtable:
158. Dictionary<k,v> has a type constraint on the added element, Hashtable can add any type of element.
160. The dictionary<k,v> does not require boxing, unpacking, Hashtable adding fashion boxes, and unpacking when reading.
164. In the Dictionary<k,v> collection, in addition to the method of obtaining a value by key, there is also a trygetvalue (key) method that can get the value by key, the return value of the method is Boolean, if there is a value corresponding to the key, returns true, otherwise returns false. Avoids exceptions that occur because the corresponding values are not obtained.
170. Using System;
172. Using System.Collections.Generic;
174. Class Program
176. {
178. static void Main ()
180. {
182. Create DICTIONARY<K,V>, and then add elements
184. Dictionary < string, string > film = new Dictionary < string, string > ();
186. Film. Add ("Wei Xiaobao", "Deer Ding kee");
188. Film. Add ("clan", "Clan Legends");
190. Film. Add ("Zhang Mowgli", "Yi Tian Tu Long kee");
192. Film. Add ("Yang-Over", "the Condor- Man");
194. Film. ADD ("Make Fox punch", "laugh proud of the Lake");
196. Console.WriteLine ("The collection now has a number of {0} elements", film. Count);
198. Film. Remove ("Yang Over");
200. Iterating through the collection
202. Console.WriteLine ("The protagonist and movie name of the martial arts film");
204. Console.WriteLine ("/t lead/t movie");
206. foreach (KeyValuePair < string, string > kvp in film)
208. {
210. Console.WriteLine ("/t{0}/t{1}", kvp. Key, kvp. Value);
212. }
214. Checks if an element exists, if it does not exist, adds
216. if (!film. ContainsKey ("Duan Yu"))
218. {
220. Film. ADD ("Duan Yu", "Tianlong Eight");
222. }
224. Gets the collection of keys
226. Dictionary < string, string >. KeyCollection keys = film. Keys;
228. A collection of traversal keys
230. Console.WriteLine ("The protagonist's name in the popular martial arts film");
232. foreach (string str in keys)
234. {
236. Console.WriteLine (str);
238. }
240. Dictionary < string, string >. ValueCollection values = film. Values;
242. Iterating over a collection of values
244. Console.WriteLine ("The most popular martial arts film");
246. foreach (string strfilm in values)
248. {
250. Console.WriteLine (Strfilm);
252. }
254. Another way to traverse an element
256. Console.WriteLine ("The same traversal element method as the hash table");
258. foreach (string strname in film. Values)
260. {
262. Console.WriteLine (strname);
264. }
266. Gets the value corresponding to the key
268. String myfilm = film["make Fox Punch"];
270. Console.WriteLine ("protagonist for the movie name of the Fox Chong {0}", myfilm);
272. TryGetValue method to get the corresponding value of the key
274. String objfilm = string. Empty;
276. if (film. TryGetValue ("Duan Yu", Out objfilm))
278. {
280. Console.WriteLine ("The protagonist for the film of the Duan Yu is {0}", objfilm);
282. }
284. Else
286. Console.WriteLine ("No protagonist for the film of the paragraph Reputation");
288. Console.readkey ();
290. }
292. }
298. The code creates a Dictionary<k,v> collection, the data type of the key and the value is a string type, the element behind the code is added, the deletion is the same as the hash table processing method, and the data type cast is not required to traverse the element. Dictionary<k,v> by the TryGetValue method of the key value, this method includes two parameters, one to query the key, and the other to get the value, note the value before using the Out keyword.
302. Note: When using the TryGetValue method, the parameter must use the Out keyword, otherwise the compilation fails.
306. Original link: http://www.code-design.cn/article/20120210/csharp-generic-collection-dictionary.aspx

C # Generic collection of dictionary<k, v> usage tips