A detailed example of the use of C generic Dictionary

This article provides an example of the use of the generic Dictionary in C#. It has very good practical value. Share to everybody for everybody reference. The details are as follows:

The most common use of generics is for generic collections. The namespace ES5en.Collections.Generic contains 1 collection class based on generics. Using generic collection classes can provide higher type safety, as well as higher performance, avoiding repeated boxing and unboxing of non-generic collections.

Many non-generic set classes have generic set classes. Here are the common non-generic set classes and their generic set classes:

The non-generic collection classes we use are ArrayList and HashTable. We often use HashTable to store the information to be written to the database or returned. In between, we need to carry out type transformation constantly, which increases the burden of system boxing and unboxing. If the data type we are manipulating is relatively certain, we use Dictionary < TKey,TValue > For example, when we need to store the user's shopping cart information (item name, corresponding number of items) in the e-commerce website, we can use Dictionary completely < string, int > To store shopping cart information without any type conversion.
Here are some simple examples, including declaring, populating, removing, and traversing key and value pairs:

Dictionary<string, string> myDic = new Dictionary<string, string>();
myDic.Add("aaa", "111");
myDic.Add("bbb", "222");
myDic.Add("ccc", "333");
myDic.Add("ddd", "444");
// If I add an existing key, add Method throws an exception 
try
{
 myDic.Add("ddd","ddd");
}
catch (ArgumentException ex)
{
 Console.WriteLine(" This key already exists: " + ex.Message);
}
// To solve add() The exception method is to use ContainsKey() Method to determine whether a key exists 
if (!myDic.ContainsKey("ddd"))
{
 myDic.Add("ddd", "ddd");
}
else
{
 Console.WriteLine(" This key already exists: ");
 
}
 
// With an indexer for negative values, if the build already exists, the key value of the existing key is changed without throwing an exception 
myDic ["ddd"]="ddd";
myDic["eee"] = "555";
 
// When using an indexer to value, an exception is thrown if the key does not exist 
try
{
 Console.WriteLine(" A bond that doesn't exist ""fff"" The key value of is: " + myDic["fff"]);
}
catch (KeyNotFoundException ex)
{
 Console.WriteLine(" No key found throws an exception: " + ex.Message);
}
// The solution to the above exception is to use ContarnsKey()  To determine when there is a key, if you often want to take the value of the best use  TryGetValue Method to get the corresponding key value in the collection 
string value = "";
if (myDic.TryGetValue("fff", out value))
{
 Console.WriteLine(" A bond that doesn't exist ""fff"" The key value of is: " + value );
}
else
{
 Console.WriteLine(" The key value for the corresponding key was not found ");
}
 
// The following use foreach  To iterate over the key-value pairs 
// Generic structs   Used to store value pairs 
foreach (KeyValuePair<string, string> kvp in myDic)
{
 Console.WriteLine("key={0},value={1}", kvp.Key, kvp.Value);
}
// Get the value set 
foreach (string s in myDic.Values)
{
 Console.WriteLine("value={0}", s);
}
// Get worth another 1 Kind of way 
Dictionary<string, string>.ValueCollection values = myDic.Values;
foreach (string s in values)
{
 Console.WriteLine("value={0}", s);
}

Common properties and methods are as follows:

<?xml version="1.0" encoding="UTF-8"?>
<data>
 <resource key="123">foo</resource>
 <resource key="456">bar</resource>
 <resource key="789">bar</resource>
</data>
i want to put this into a Dictionary (sorted) as key value pairs. i.e: 123:foo, 456:bar...etc
the keys are unknown.
 
string s = "<data><resource key=/"123/">foo</resource><resource key=/"456/">bar</resource><resource key=/"789/">bar</resource></data>";
 XmlDocument xml = new XmlDocument();
 xml.LoadXml(s);
 XmlNodeList resources = xml.SelectNodes("data/resource");
 SortedDictionary<string,string> dictionary = new SortedDictionary<string,string>();
 foreach (XmlNode node in resources){
 dictionary.Add(node.Attributes["key"].Value, node.InnerText);
 }

linq to xml:
var xml = XDocument.Load(...);
var sequence = from e in xml.Root.Elements() 
let key = (string)e.Attribute("key")
order by key
select new { 
 Key = key, 
 Value = (string)e 
};

Hopefully this article has helped you with your C# programming.