7 Common uses of dictionary generic collections in C #

To use the dictionary collection, you need to import a C # generic namespace

System.Collections.Generic (assembly: mscorlib)

Description of the Dictionary
1, from a set of keys (key) to a set of values (value) of the mapping, each add-on is a value and its associated key composition

2. Any key must be unique

3, the key cannot be null reference null (Nothing in VB), if the value is a reference type, you can be a null value

4, key and value can be any type (String,int,custom class, etc.)

Dictionary Common usage: the type of key is int, the type of value is string, for example

1. Create and initialize

The code is as follows:

Dictionary<int,string>mydictionary=newdictionary<int,string> ();

2. Adding elements

The code is as follows:

Mydictionary.add (1, "C #");
Mydictionary.add (2, "C + +");
Mydictionary.add (3, "ASP.");
Mydictionary.add (4, "MVC");

3. Find elements by key

The code is as follows:

if (Mydictionary.containskey (1))
{
Console.WriteLine ("Key:{0},value:{1}", "1", mydictionary[1]);
}

4. Traversing elements through KeyValuePair

The code is as follows:

foreach (keyvaluepair<int,string>kvp in mydictionary)
{
Console.WriteLine ("Key = {0}, Value = {1}", kvp. Key, kvp. Value);
}

5. Only the key Keys property is traversed

The code is as follows:

Dictionary<int,string>. KeyCollection Keycol=mydictionary.keys;
foreach (Intkeyinkeycol)
{
Console.WriteLine ("key = {0}", key);
}

6. Traverse only the Value Valus property

The code is as follows:

Dictionary<int,string>. ValueCollection valuecol=mydictionary.values;
foreach (Stringvalueinvaluecol)
{
Console.WriteLine ("value = {0}", value);
}

7. Remove the specified key value through the Remove method

The code is as follows:

Mydictionary.remove (1);
if (Mydictionary.containskey (1))
{
Console.WriteLine ("Key:{0},value:{1}", "1", mydictionary[1]);
}
Else
{
Console.WriteLine ("Non-existent key:1");
}

  description of other common properties and methods:

Comparer:	gets the iequalitycomparer used to determine whether the keys in the dictionary are equal.
Count:	Gets the number of key/value pairs contained in the dictionary.
Item:	Gets or sets the value associated with the specified key.
keys:	Gets the collection that contains the keys in the dictionary.
values:	Gets a collection that contains the values in dictionary.
add:	adds the specified key and value to the dictionary.
Clear:	removes all keys and values from dictionary.
containskey:	Determines whether dictionary contains the specified key.
containsvalue:	Determines whether dictionary contains a specific value.
getenumerator:	Returns an enumerator that iterates through the dictionary.
GetType:	Gets the Type of the current instance. (Inherit from Object.)
Remove:	Removes the value of the specified key from dictionary.
ToString:	Returns a String that represents the current object. (Inherit from Object.)
TryGetValue:	Gets the value associated with the specified key.

Common use of dictionary generic collections in C # 7