How to decide when to use which design pattern?

When to use design patterns?

Using design patterns is a common software architecture practice when new software is being designed and architected. Software architects use design patterns in software engineering, but not every software project needs a pattern. This article explains when to use design patterns and which design pattern should be used in what situation. 

Design patterns should be used when facing a common software design problem. Design patterns provide proven solutions to these problems, which can help you write more efficient, maintainable, and flexible code.

Here are some specific situations where you might want to consider using a design pattern:

• When you need to design a system that is flexible and extensible.
• When designing a system that can be easily reused in different contexts.
• When you need to design a system that is easy to maintain and update.
• When you need to design a system that is efficient and performant.
• When you need to design a scalable system that can handle large amounts of data and traffic.

Here are some examples of specific design patterns that you might want to use in different situations:

• The Singleton pattern can ensure that only one instance of a particular object exists in a system.
• The Factory pattern can be used to create objects without specifying the object's specific class.
• The Observer pattern can be used to decouple objects that need to communicate with each other.
• The Strategy pattern can be used to allow different algorithms to be used to solve the same problem.
• The Adapter pattern can be used to make incompatible objects work together.

It is important to note that design patterns should not be used blindly. You should only use a design pattern if it is the best solution to the specific problem that you are trying to solve.

Here are some tips for using design patterns effectively:

• Choose the right design pattern for the job. There is no one-size-fits-all design pattern.
• Understand the problem you are trying to solve before choosing a design pattern.
• Don't overuse design patterns. Too many design patterns can make your code complex and difficult to maintain.
• Use design patterns consistently. This will make your code more readable and maintainable.

If you are new to design patterns, I recommend learning design patterns here: Design Patterns In C# .NET (2023) (c-sharpcorner.com)

When to use which design pattern

Certainly! Design patterns are general reusable solutions to common problems that occur in software design. They are not blueprints or templates but rather guidelines on how to solve a problem flexibly and maintainable. I'll go through some of the most commonly used design patterns, explaining them in layman's terms and real-world examples to make them easier to understand.

Creational Patterns

Singleton

• When to Use: When you want to ensure that a class has only one instance and provide a global point to access it.
• Real-world Example: A logging system where you want a single object that handles the log, to avoid multiple objects overwriting the log.

Factory Method

• When to Use: When you have a super class with multiple sub-classes, and based on input, you must return one class instance.
• Real-world Example: Payment gateway integration where the payment method (Credit Card, PayPal, Bitcoin) is chosen at runtime.

Abstract Factory

• When to Use: Similar to the Factory Method, a family of related or dependent objects is created here.
• Real-world Example: User interface libraries where you have multiple themes; each theme has its variety of buttons, windows, and other elements.

Structural Patterns

Adapter

• When to Use: When you want to make one class look like another class.
• Real-world Example: Memory card adapters; the memory card from your camera might not fit into your laptop, so you use an adapter that makes it compatible.

Composite

• When to Use: When you want to treat both individual objects and compositions of objects uniformly.
• Real-world Example: Graphic systems that have shapes like circles, rectangles and triangles, but also groups of shapes like diagrams.

Proxy

• When to Use: When you want to provide a surrogate or placeholder for another object to control access to it.
• Real-world Example: Lazy loading of a large image collection; thumbnails are proxies for full-size images.

Behavioral Patterns

Observer

• When to Use: When you need many other objects to receive an update when another object changes.
• Real-world Example: A weather station that notifies multiple displays whenever it takes a new measurement.

Strategy

• When to Use: When you want to define a family of algorithms, encapsulate each one of them and make them interchangeable.
• Real-world Example: Sorting algorithms. You could switch between quicksort, mergesort, and bubblesort dynamically.

State

• When to Use: When an object should change its behavior when its internal state changes.
• Real-world Example: A traffic light that changes its actions based on its current state (red, green, yellow).

Command

• When to Use: When you want to parameterize objects with operations, delay the execution of an operation, or put the request for an operation into a queue.
• Real-world Example: Remote controls. Each button press is a command decoupled from the device it controls, allowing for flexibility and configurability.

Understanding when to use a particular design pattern largely comes with experience and the specific needs of the project you are working on. Some projects may not require any design patterns, or you may find that a combination of patterns best solves your problem. The aim is to make the code more maintainable, flexible, and understandable.

Here is a tutorial on design patterns with code examples: Design Patterns In C# .NET (2023)