Event Driven - Prelim

Delegates

A class in .NET that encapsulates a method and holds a reference to a method.

delegate keyword

Used in declaring a delegate on a class.

Syntax for Delegate Declaration

delegate ()

Instantiation of Delegate

Use the new keyword associated with the method to create an instance.

Generic Delegates

Delegates that are not bound to any specific type and can reference methods of different types.

Difference between Delegate and Interface

Delegates have no implementation, while interfaces can implement methods.

Event

A member of a class that is fired whenever a specific action takes place.

Event Handlers

Methods that are invoked when an event occurs.

Adding an Event

Use the syntax eventname += delegateinstance.

Removing Event Subscription

Use the remove accessor to unregister a subscription.

Collections

Groups of objects that include lists, linked lists, dictionaries, and arrays.

Standard Collections

Found in the System.Collections namespace.

Generic Collections

Found in the System.Collections.Generic namespace.

ArrayList

A collection class known for an ordered collection of objects that is dynamic.

Hashtable

Stores key-value pairs where the key represents the value in the collection.

SortedList

A combination of ArrayList and Hashtable that stores key-value pairs sorted by key.

Capacity (SortedList)

Gets or sets the capacity of the SortedList.

Count (SortedList)

Gets the count of the number of elements in the SortedList.

Item (SortedList)

Gets and sets the value associated with a specific key in the SortedList.

Keys (SortedList)

Holds the keys in the SortedList.

Values (SortedList)

Holds the values in the SortedList.

Add method (SortedList)

Adds an item with the specified key and value into the SortedList.

Clear method (SortedList)

Removes all the items in the SortedList.

ContainsKey method (SortedList)

Returns true if the SortedList contains the specified key.

ContainsValue method (SortedList)

Returns true if the SortedList contains the specified value.

GetByIndex method (SortedList)

Returns the value of the specified index.

GetKey method (SortedList)

Returns the key of the specified index.

Remove method (SortedList)

Removes the element with the specified key from the SortedList.

RemoveAt method (SortedList)

Removes an element at the specified index in the SortedList.

Stack

Represents a Last In, First Out (LIFO) collection of objects.

Queue

Represents a First In, First Out (FIFO) collection of objects.

IEnumerable interface

Allows looping through elements in a collection.

ICollection interface

Determines the number of elements in a collection and can copy them into an array.

IDictionary interface

Provides a list of elements accessible via a key or value.

Generics

Allows code reuse across different types by creating a template with placeholder types.

System.Collections.Generic namespace

Contains several generic collection classes.

List

A generic collection that provides an efficient and dynamically allocated array.

Add() method (List)

Adds items to the end of a list.

Remove() method (List)

Removes the specified item from the list.

IndexOf() method (List)

Checks for the specified element and returns its index value.

Sort() method (List)

Sorts elements in the list.

Queue

A generic collection representing a FIFO collection of objects.

Enqueue() method (Queue)

Adds an element to the end of the queue.

Peek() method (Queue)

Returns the element at the beginning of the queue without removing it.

Dequeue() method (Queue)

Removes and returns the value at the beginning of the queue.

Stack

A generic collection that represents a LIFO collection of instances.

Push() method (Stack)

Adds an element at the top of the stack.

Peek() method (Stack)

Returns the element at the top of the stack without removing it.

Pop() method (Stack)

Removes and returns the value at the top of the stack.

Difference: Delegate Implementation

Delegates have no implementation while interfaces can implement methods associated with them.

Usage of Delegates

Used in classes where multiple implementations of methods are needed.

Performance of Delegates vs Interfaces

Delegates are faster to execute but slower to acquire, interfaces are slower to execute but faster to acquire.

Subscription to Events

Registered using add accessor for events.

Removing Subscriptions to Events

Done using the remove accessor associated with the event.

ArrayList vs Static Array

ArrayList is dynamic; a static array has a fixed size.

Hashtable Key Requirement

Keys must be specified to access corresponding values in Hashtable.

SortedList Access Requirements

Key or index value must be specified to access values in SortedList.

SortedList Method: Add

Adds a key-value pair to the SortedList.

SortedList Method: RemoveAt

Specifies index to remove the element in the SortedList.

Stack Behavior

LIFO, utilizing push and pop operations.

Queue Characteristics

FIFO, utilizing enqueue and dequeue operations.

IEnumerable Functionality

Provides iteration capabilities for collections.

Generics Purpose

To enhance code reusability by specifying data types at runtime.

List Capacity

Can dynamically grow or shrink based on object quantity.

Generic Method Example: Add() in List

nameOfStud.Add("Rose"); to add a student.

Generic Method Example: Remove() in List

nameOfStud.Remove("Mike"); to remove a specified student.

Generic Method Example: IndexOf() in List

Console.WriteLine(nameOfStud.IndexOf("Rose")); to find index.

Generic Method Example: Sort() in List

nameOfStud.Sort(); to sort the student names.

Queue Object Example

Queue ageQueue = new Queue(); to create a queue of integers.

Queue Method Example: Enqueue()

ageQueue.Enqueue(18); to add an age to the queue.

Queue Method Example: Peek()

ageQueue.Peek(); to get the first age without removing.

Queue Method Example: Dequeue()

int getValue = ageQueue.Dequeue(); to remove and get the first age.

Stack Object Example

Stack ageStack = new Stack(20); to create a stack.

Stack Method Example: Push()

ageStack.Push(18); to add age to the top of the stack.

Stack Method Example: Peek()

int getValue = ageStack.Peek(); to get the top age without removing.

Stack Method Example: Pop()

int getValue = ageStack.Pop(); to remove and get the top age.