Collections and Generics in C#

Maker QR in C# Collections and Generics

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For Each i as KeyValuePair(Of String, Integer) in sortList Console.WriteLine(i) Next // C# SortedList<string, int> sortList = new SortedList<string, int>(); sortList["One"] = 1; sortList["Two"] = 2; sortList["Three"] = 3; foreach (KeyValuePair<string, int> i in sortList) { Console.WriteLine(i); }

The use of the SortedDictionary is identical. To use a SortedDictionary, follow these steps: 1. Create an instance of SortedDictionary, specifying the key and value generic type parameters. 2. You can use indexer syntax to add or retrieve items in the SortedDictionary, but they must match the types specified in the generic type parameters of the SortedDictionary. 3. Create a foreach structure, specifying a generic KeyValuePair class as the type of object to be returned in each iteration. The types specified in the KeyValuePair must match the types used in the original SortedDictionary. 4. Inside the foreach block, you can use the KeyValuePair to retrieve the keys and values with properties called Key and Value, respectively. This example stores integers as the keys and strings as the values of the SortedDictionary:

' VB Dim sortedDict as new SortedDictionary(Of String, Integer)() sortedDict("One") = 1 sortedDict("Two") = 2 sortedDict("Three") = 3 For Each KeyValuePair(Of string, int) i in sortedDict Console.WriteLine(i) Next // C# SortedDictionary<string, int> sortedDict = new SortedDictionary<string, int>(); sortedDict["One"] = 1; sortedDict["Two"] = 2; sortedDict["Three"] = 3;

foreach (KeyValuePair<string, int> i in sortedDict) { Console.WriteLine(i); }

The generic LinkedList class is a type of collection that is new to .NET, though the concept is well worn and tested. In fact, I remember writing a LinkedList in college. The idea behind a linked list is a set of items that are linked to each other. From each item, you can navigate to the next or previous item without having to have access to the collection itself. This is very useful when you are passing objects around that need to know about their siblings. Table 4-21 and Table 4-22 show the interface to the generic LinkedList class:

Description Gets the number of nodes in LinkedList Gets the first node in LinkedList Gets the last node in LinkedList

Description Adds a new node after an existing node in LinkedList Adds a new node before an existing node in LinkedList Adds a new node at the beginning of LinkedList Adds a new node at the end of LinkedList Removes all nodes from LinkedList Tests to see whether a value is contained within LinkedList Copies the entire LinkedList to an Array Locates the first node containing the specified value Locates the last node containing the specified value

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Description Removes the first occurrence of a value or node from LinkedList Removes the first item from LinkedList Removes the last item from LinkedList

A LinkedList contains a collection of LinkedListNode objects. When working with a LinkedList, you will be primarily getting and walking down the nodes. The properties of the generic LinkedListNode class are detailed in Table 4-23.

Description Gets the LinkedList that the node belongs to Gets the next node in the LinkedList Gets the previous node in the LinkedList Gets the value contained in the node.

One peculiarity of the generic LinkedList class is that the implementation of the enumerator (ILinkedListEnumerator) allows for enumeration of the values of the list without using LinkedListNode objects. This behavior is unlike the generic Dictionary type, where the enumerator returns a generic NameValuePair object. The difference exists because LinkedListNode objects can be used to walk the list of items, but only one piece of data is in each node. Therefore, there is no need to return the nodes during enumeration. To use a LinkedList, you can create an instance of the LinkedList class, specifying the type to be stored as values in the list, then you can perform any of the following actions:

You can use the AddFirst and AddLast methods to add items to the beginning and end of the list, respectively. The AddFirst and AddLast methods return a LinkedListNode if you are simply specifying the value in these methods. You can also use the AddBefore and AddAfter methods to add values in the middle of the list. To use these methods, you need to have access to a LinkedListNode at which you want to add values before or after.