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Understanding iOS design patterns
Design patterns help developers follow best practices to simplify and streamline the development process

Although design patterns might not be glamorous, and they might not get much attention from the majority of developers, they are highly important. Design patterns are reusable solutions for common problems in software design. A design is essentially a template that helps the developers to write code that is both easy to understand and to reuse. In addition, the use of design patterns makes it possible for the developer to make changes to or replace elements of the code with relative ease and speed.

Those who are developing using Cocoa will find that they are already making use of iOS patterns due to the way Cocoa has been built. These design patterns are in place to help the developers follow best practices to simplify and streamline the development process.

Major Benefits of iOS Design Patterns

All the patterns can provide a range of advantages to the developers who choose to use them. One of the first and most important of these benefits is the unification of the code. The use of patterns can also highlight and identify mistakes during coding and developing the structure of the app architecture.

Indicating the design pattern that was used helps anyone else who is working on the project to understand the solutions that have been incorporated. Essentially, using the design patterns, and indicating the pattern used, puts everyone on the same page. Design patterns for iOS indicate how developers should move forward and incorporate the best solutions for the project while solving specific issues with the software. This reduces the amount of time that developers need to spend finding and fixing problems in the project.

Categories for Design Patterns

There are three categories into which iOS patterns fall - creational, structural, and behavioral. Different patterns will naturally have different functions and will be used for different purposes. Below, we will look at several iOS patterns in each of these categories.

Creational Design Patterns

Creational design patterns provide the development team with object development mechanisms. The pattern gives a simple way of creating objects, including complex ones. The design patterns make these creations understandable and maintainable for the developers. It will also hide certain details, such as instantiation and class implementation. There are a number of different types of creational design patterns that are used today, including Singleton, Factory Method, Abstract Method, and Builder Method.

Singleton Pattern

The Singleton design pattern is used to ensure that there is only a single instance for a given class. It also ensures that there will be a global access point for the instance. There are many cases where you might need to have only a single instance of a class in iOS devices, including FileManager.default, UIApplication.shared, and UserDefaults.standard.

The Singleton Pattern can be beneficial, but it can also be easy for people to overuse. It is not the best solution for those who are attempting to pass information from one controller to another. Developers should be careful and make sure they do not need to have multiple custom instances, for example. If that’s the case, creation as a regular object is often the better solution for the development team.

Factory Pattern

Another option that falls into the creation category for iOS patterns is the Factory Pattern in Swift. When using this pattern, developers can create objects without the need to specify the exact class of the object that is being created. This design is used when creating objects instead of a direct constructor call.

The Factory Pattern will allow the client that received the created object to use it through the common interface. It will not care about the type of concrete object that is actually created. Factory Pattern separates the details of creating objects from the common interface. Ultimately, this will help to remove many of the difficulties that are often involved when it comes to creating objects that might need to behave in a similar fashion. The reusable code that is created also tends to be easier to maintain.

Abstract Pattern

An Abstract Pattern is a type of Factory Pattern. They will be able to provide an interface that will allow for the creation of families of objects that are related or independent. They will not need to have any specification for their concrete classes. Another term for this is Class Cluster design.

With the Abstract Pattern, there will be a public class for use in the application code. Whenever the application code attempts to create an instance of the public class, there will be an instance of the private subclass created.

Builder Pattern

The Builder Pattern allows for the construction of complex objects step by step. The same structure can be used to create different types of objects, including groups of data and instructions. It is possible to encapsulate the code for construction, and create various objects while using the same basic construction process.

The Builder Pattern is common when using Swift and makes it possible to create a large number of configuration options.

The use of the Builder Pattern will also help to make objects that are more predictable and simpler. The objects that are created with the pattern will be stateless, which translates to them being easier to test and debug. The logic for these patterns contains only pure input and output.

There are some aspects with iOS projects that will follow this type of pattern, such as Date Components and URL Components.

Structural Design Patterns

Structural Design Patterns are used as a means to help simplify the process of designing the architecture of an iOS app. The goal is to find simpler methods to correlate classes and objects.

MVC Pattern

The Model View Controller (MVC) pattern is one of the most important design patterns used for iOS development for the iPhone and other iOS devices. This pattern will specify that applications consist of a data model, presentation info, and control info. Using this pattern requires that the development team separate each of those into different objects.

MVC works well as an architectural pattern, meaning that it can provide a strong skeleton from which the developers can build out their project. It will relate to the user interface/interaction layer of the application. Those who are developing the application will also need to have other layers, such as a business logic layer and data access layer, for example.

Decorator Pattern

The purpose of the Decorator Pattern is to add responsibilities and behaviors to an object dynamically and without altering the code. There are some who call this a wrapper pattern. This design can be used instead of sub-classing, which would require wrapping it with another object in order to modify a class’s behavior. This pattern is often used to adhere to the single responsibility principle since it can allow for a division of functionality between classes.

It is also very similar to a chain of responsibility pattern. The only major difference is that with the chain of responsibility pattern, one of the classes will handle the request. With the Decorator Pattern, all classes will handle the request. Using a decorator pattern lets developers alter behavior or add a behavior of an interface during run-time.

Adapter Pattern

The Adapter Pattern is sometimes called a wrapper, which can be somewhat confusing, as this is also a name that developers will sometimes use for the Decorator Pattern. It will allow for the interface of a class that already exists to be used as another interface. Often, this pattern is used as a way to make existing classes work together without making any modifications to the source code, which helps to speed up work on the project.

Tthe Adapter Pattern helps developers to reuse a class that might not have an interface that the client requires. It can help incompatible interfaces work together, and it can provide an alternative interface for a class.

Façade Pattern

Here is another design pattern for iOS that is quite common. The Façade Pattern provides a simplified interface for complex systems. Rather than showing a large number of methods with various interfaces, it is possible to include other objects into a class that’s created. This can help to simplify the interface. The object is the interface that is front-facing, similar to the façade of a building. The underlying code is behind this façade.

Façade Pattern provides a number of benefits. It can provide a simple interface, even when accessing a system that is complex. The pattern can serve well as an entry point into different levels of a layered application.

Behavioral Design Patterns

Behavioral design patterns are commonly useful in regard to communication patterns within the applications and interfaces. There are a number of different types of behavioral design patterns in use in app development today, including those below.

Observer Pattern

An observer pattern features an object that maintains a list of its dependents. These are used when there is a one-to-many relationship, where the dependent objects within the main object need to be automatically notified. There are three actor classes in this type of pattern, including the subject, observer, and client. The subject is an object that has methods of attaching and detaching observers to a client object.

Memento Pattern

This behavioral design pattern is used as a means to help restore the state of an object to a previous state. The design components featured in this type of pattern include the originator, which is the object for which the stat is to be saved. This will create a memento, which is the object that will keep the state of the originator. There is also a caretaker, which can help to keep track of multiple mementos.

Template Pattern

The Template Pattern is a design pattern that will define an algorithm as the bare-bones architecture of operations. The details of the application will be implemented through the child classes that are added to it. The template pattern is common with Swift frameworks. The subclasses that are added to it will help to refine parts of the algorithm, but the structure will remain the same.

Command Pattern

The Command Pattern is used for request encapsulation, which will allow for the separation of an object, sending a message from the objects that receive the message. This allows that message to be more flexible. It could be stored for usage later, passed between objects, modified dynamically, and more. They can be used for “undo management” and to encapsulate messages. The Command Pattern will contain a target, selector, arguments, and a return value.

Design patterns help to make the development of apps for the iPhone easier and faster for developers. They have a range of benefits that could be used to reduce the costs and the difficulty of creating applications, which is why so many development teams implement them. The brief overview of the various types of design patterns used for iPhones and other iOS devices should help to give you a better understanding of what they are and how they are implemented.

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