Design patterns aim to simplify the code writing for developers. They help to provide an easy and efficient work process for programmers. Design patterns are sequences of repeatable processes that are used to develop software solutions.
The patterns are templates that are suitable for solving particular problems. They also help to reduce potential errors that can appear during the testing phase and therefore making the testing more productive. So design patterns aim to write simple and maximally clean code that fastens the development process but still gives a high-quality solution.
There are 23 main iOS design patterns and all of them are divided into 4 groups:
- software architecture.
We would like to describe the peculiarities and usage of each iOS design pattern in this article further. Though, we would like to begin with defining the key benefits of design pattern use and how they simplify the coding process.
Benefits of iOS Design Patterns
As we have already figured out, design patterns are used to make code writing easier and more effective. Among the key advantages of design patterns should be mentioned:
- Code unification.
- Defining and showing the bugs and potential problems during the coding or building the solution architecture.
- Design patterns show the way developers should move and what solutions they should include to avoid repeatable errors in the future.
- Design patterns quickly define the error and save time to fix them.
One of the most popular adaption ways of design patterns is through Cocoa as their mechanisms are common in Cocoa frameworks.
We also recommend you to check out the video below and find out more information on what design patterns are and why they are essential for software developers.
Creational design patterns
Creational group of design patterns includes 4 patterns:
These methods are responsible for object creation in an easy way even if the objects have complex structures. Therefore, these objects are more clearly identified by developers.
This design method is required when you need to copy only one element from the whole pattern. It defines all objects on the screen and offers multiple features like copying it particular object one time or several times choosing the right place for the copied element, etc. As an example, it can be an iOS-based UseDefaults object.
Singletons are best when you need to manage resources. For example, HTTP connections. You don’t want to establish 1 million HTTP clients to a single client, that is crazy wasteful and slow. So a singleton with a connection pooled HTTP client will be much faster and resource-friendly.
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This design function helps to choose the suitable class for the pattern. It can be a common base or common (global) protocol. This method acts logically and has two ways of implementation that we named previously.
It is a good idea to use factory methods inside an object when:
- object’s class doesn’t know what exact sub-classes it has to create;
- object’s class is designed so that objects it creates were specified by sub-classes;
- object’s class delegates its duties to auxiliary sub-classes and doesn’t know what exact class will take these duties.
Abstract factory pattern has similar options to the Factory pattern. It does not define the implementation class but helps to create a group (family) of objects and select the suitable one. This pattern is also called Class Cluster. The abstract pattern provides a public class in the app code.
It is a good idea to use abstract factory class when:
- Your object shouldn’t depend on how its inner objects are created and designed.
- Group of linked objects should be used together and you need to serve this constraint.
- The object should be configured by one of several possible families of linked objects that will be a part of your parent object.
- It is required to share child objects showing interfaces only but not an implementation.
Builder is an iOS-based pattern that is used to divide objects and configuration. The builder pattern is responsible for object creation, groups of data, and instructions. The builder pattern is mostly used with Swift and provides the ability to create vast numbers of configuration options. This pattern also makes the objects more clear and simple, easier to test and debug.
The Builder pattern can be applied when the construction of various representations of the product involves similar steps that differ only in the details. The base builder interface defines all possible construction steps, and concrete builders implement these steps to construct particular representations of the product. Meanwhile, the director-class guides the order of construction.
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Structural design patterns
Structural design patterns aim to simplify the design of app architecture that makes the process of development easier and faster for developers. Structural design patterns help to make classes and objects consistent.
The Facade is one more iOS design pattern. It simplifies the complex interfaces. To provide an easy and user-friendly interface, the facade method helps to create own class by adding objects to it to avoid a huge number of interfaces. It means that you can edit the facade pattern ( only one class) without changing the entire interface so users don’t notice these changes. Often, subsystems get more complex over time. Even applying design patterns typically leads to creating more classes. A subsystem may become more flexible and easier to reuse in various contexts, but the amount of configuration and boilerplate code it demands from a client grows ever larger.
The Facade attempts to fix the problem by providing a shortcut to the most-used features of the subsystem which fit most client requirements.
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An iOS design pattern Decorator is responsible for adding the required behavior and options to the particular object without changing its code. It is especially the needed pattern when you use the third-party database or library so you can not rewrite the code yourself. This method implies two types of integration – extensions, and delegation. This pattern also makes it possible to add the behavior of the interface. The Decorator lets you structure your business logic into layers, create a decorator for each layer, and compose objects with various combinations of this logic at runtime. The client code can treat all these objects in the same way, since they all follow a common interface
Many programming languages have the final keyword that can be used to prevent further extension of a class. For a final class, the only way to reuse the existing behavior would be to wrap the class with your own wrapper, using the Decorator pattern.
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The Adapter pattern provides the communication of interfaces that don’t match with each other. It is a process of object implementation when you can not rewrite the code. It works great with the products that legally forbid code modifying.
The Adapter pattern lets you create a middle-layer class that serves as a translator between your code and a legacy class, a 3rd-party class, or any other class with a weird interface.
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Bridge iOS Develop pattern can be compared to the adapter as they have some similarities. However, it has advanced options. Bridge lets code change only if you have full access to it. The code modifying happens in one class as they can be separated due to bridge pattern, so other classes will not be notified about changes. The bigger a class becomes, the harder it is to figure out how it works, and the longer it takes to make a change. The changes made to one of the variations of functionality may require making changes across the whole class, which often results in making errors or not addressing some critical side effects.
The Bridge pattern lets you split the monolithic class into several class hierarchies. After this, you can change the classes in each hierarchy independently of the classes in the others. This approach simplifies code maintenance and minimizes the risk of breaking existing code.
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Behavioral design patterns are commonly used to provide communication between patterns, apps, and interfaces. The number of behavioral design patterns is large. We covered the most frequently used pattern for building iOS applications today here below.
The Observer Swift design pattern provides notifications about object state changing. It defines the object dependency according to other objects. The Observer pattern shows a publish-and-subscribe model. You can often experience this problem when working with classes of the graphical user interface. For example, you created custom button classes, and you want to let the clients hook some custom code to your buttons so that it fires whenever a user presses a button.
The Observer pattern lets any object that implements the subscriber interface subscribe for event notifications in publisher objects. You can add the subscription mechanism to your buttons, letting the clients hook up their custom code via custom subscriber classes.
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The Memento saves your objects, such as UserDefaults, Archiving, and NSCoding protocol, using the CoreData. However, private data remains private in any case. This design pattern is mostly used to help re-establish objects to previous states. This includes the originator that defines the state that should be saved, and it is called memento. Caretaker helps to monitor the numbers of mementos.
The Memento pattern lets you make full copies of an object’s state, including private fields, and store them separately from the object. While most people remember this pattern thanks to the “undo” use case, it’s also indispensable when dealing with transactions (i.e., if you need to roll back an operation on an error).
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When we connect a method to an action touch for any interface ( buttons), this is the Command pattern. This pattern lets customize clients’ requests, log requests. support and other operations. The command divides object creation requests and objects that execute this request. The Command pattern can turn a specific method call into a stand-alone object. This change opens up a lot of interesting uses: you can pass commands as method arguments, store them inside other objects, switch linked commands at runtime, etc.
Software architecture patterns
MVC Design Pattern
What is MVC design pattern in iOS? The Model View Controller or MVC is considered to be a crucial design pattern in iOS app development. Using this pattern means that the application contains data model, presentation, and control info. This pattern divides each object. MVC pattern builds the entire app architecture that simplifies the development process and is responsible for interface and product interaction.
The Model View Presenter or MVP consists of:
- passive view
An alternative to the “Massive” VC problem is to implement an MVP Model. MVP stands for Model View Presenter and is, at its core, an effective way to move much of the logic from ViewController files and instead replace it with a call to a presenter. This means everything on Presenter file is testable and easy to access and read.
MVVM is a structural design pattern. Imagine that you have two views with a different layout that needs to be populated with data from the same model class. MVVM allows you to use data from a single model class and represent it in different ways to populate a view.
Components Overview and their roles are the following:
- View Controller: It only performs things related to UI — Show/get information. Part of the view layer
- View Model: It receives information from VC, handles all this information, and sends it back to VC.
- Model: This is only your model, nothing much here. It’s the same model as in MVC. It is used by VM and updates whenever VM sends new updates
Viper is a popular design pattern that implements the ‘separation of concern’ paradigm. Mostly like MVP or MVC, it follows a modular approach. One feature, one module. For each module, VIPER has five different classes with distinct roles. No class goes beyond its sole purpose. These classes are as follows.
- View: Class that has all the code to show the app interface to the user and get their responses. Upon receiving a response View alerts the Presenter.
- Presenter: Nucleus of a module. It gets user responses from the View and works accordingly. The only class to communicate with all the other components. Calls the router for wire-framing, Interactor to fetch data (network calls or local data calls), view to update the UI.
- Interactor: Has the business logic of an app. e.g if business logic depends on making network calls then it is Interactor’s responsibility to do so.
- Router: Does the wire-framing. Listens from the presenter about which screen to present and executes that.
- Entity: Contains plain model classes used by the Interactor.
How to select a design pattern?
Due to the vast choice of design patterns, there are some things worth considering when selecting the design patterns. We would like to highlight the key steps in choosing the suitable design pattern in the list below.
We strongly recommend you to get a professional consultation with our software architects. The design pattern selection is a responsible task as it defines the further development flow. Our experienced developers will discuss the peculiarities of your solution, help to define the main business objectives and problems that should be resolved. Therefore, you will successfully come to the right choice of design patterns for your solution.
- What problems need to be solved?
- How can these patterns solve my problems?
- Figure out the patterns` purposes and if they can be combined.
- Think of your design – what elements should be able to change.
To end up
As we have already figured out, iOS design patterns aim to simplify iOS-based software development. Design patterns provide a range of benefits that we covered above, particularly, they help to save costs and simplify the development of an application. That is the main cause of design pattern implementation. If you are looking for a way of simplifying the development stages, we would like to offer you a free professional consultation with our iOS developers who will make proper research for your solution and propose an effective and easy way of its realization.