What's the best behavioral design pattern for your project?

For defining a dynamic algorithm, the Strategy design pattern might be your best bet. The Strategy pattern allows you to define a family of algorithms, encapsulate each one of them, and make them interchangeable. This way, you can select an algorithm dynamically at runtime, depending on the context or the conditions of your project.

interface IObserver { public void Notify(); } interface IObservable { public void Subscribe(IObserver); } class TechChannel : IObservable { List<IObserver> mysubscribers = new(); public void Subscribe(IObserver observer) { mysubscribers.Add(observer); } public void NewVideoPublished() { foreach(IObserver observer in mysubscribers) observer.Notify(); } } class UserType1 : IObserver { public void Notify() { //WatchVideo(); } } class ClientType2:IObserver { public void Notify() { //DownloadVideo(); } } class BusinessObject { IObservable channel = new TechChannel(); channel.Subscribe(new UserType1()); channel.Subscribe(new ClientType2()); }

The best design pattern for notifying multiple objects about a state change is the Observer pattern. This pattern establishes a one-to-many relationship between a subject and its observers, allowing the subject to automatically notify and update all subscribed observers when its state changes. For instance, in a scenario like a newsletter service notifying subscribers about new articles, the Observer pattern enables seamless communication between the publisher (subject) and subscribers (observers), ensuring they receive updates without tightly coupling their interactions.

In situations like a text editor, where you have various editing commands like cut, copy, paste, and undo, the Command pattern shines. It allows you to encapsulate these commands as objects, each representing a specific action (command). These command objects can then be passed to an invoker, which executes them on the appropriate receiver objects (e.g., text editor, document).

In scenarios like navigating a file system with folders and files, calculating the total size of a directory, the Visitor pattern comes in handy. It enables you to define a visitor class with specific operations (methods) that can handle different types of elements within the structure. Each element in the structure accepts the visitor, allowing the visitor to perform its operation on that element.

The Mediator pattern perfectly suits scenarios where multiple objects need to collaborate toward a common goal while minimizing direct dependencies. For instance, in a chat application, employing the Mediator pattern allows users to send and receive messages through an intermediary (the mediator). This mediator encapsulates the interaction logic between users, reducing tight coupling between them and streamlining communication.

Another example of Mediator pattern is the communication between different planes for landing permission on an Airport. On a busy airport like Atlanta or Mumbai, if there are 10 airplanes that are going to land and 5 which are ready to take-off, they will not talk to each other (handshake problem -> 105 communication channels in this example). Rather, the planes will be talking to the ATC tower and ATC tower will be managing the actions of Planes and the availability of the Runways and based on the availability and schedule, the ATC will instruct each plane to take-off from or land on a specific runaway at a specific time. Similarly a Call Center is used as a Mediator to book calls for a Repair service for household equipment.