In software development, design patterns are insurance against the time taken to unravel problems. The premium is that the time it takes to feature extra flexibility to your code now, and therefore the pay-out is avoiding a painful and protracted rewrite to vary the way the application works later. Like insurance policies, you will not enjoy paying the premium because the problem you anticipate might never happen, but software development rarely goes smoothly and problems often arise, so that additional flexibility is typically a good investment.
A design pattern identifies a standard software development problem and provides a technique for handling it, rather like the informal approach that I described earlier but that is expressed objectively, consistently, and free from emotional baggage.
A design pattern may be a common solution to a software problem. They are helpful for speeding up problem-solving, ensuring that a developer doesn’t have to reinvent the wheel for each situation They also give developers a standard vocabulary with which to urge across high-level ideas with minimal explanation and full understanding. Design patterns are everywhere in iOS Because iOS could also be a fairly particular platform, developers often face related problems over and over, so there are a couple of design patterns that are extremely common in iOS.
Design pattern categories in iOS
1 Creational:
From the list of design pattern categories, one of the first swift design pattern categories for iOS app development is creational design patterns. Creational swift architecture patterns are meant for building object mechanisms. The mechanism then layout concrete evidence in favor of the object. Evidence in favor then becomes suitable for a selected condition.
There are a different collections of creational design patterns in Swift like Factory, Abstract, Singleton, Builder, etc.
2 Structural:
As its name suggests, the Structural design pattern category is that the task of simplifying the app designing process while finding the simplest method for correlating objects and classes.
It comes up with different methods like Facade, Adapter, MVC, and Bridge, Decorator, etc.
3 Behavioral:
The Behavioral design pattern category is the communication pattern between units and the integration of patterns is gained through behavioral design patterns, Swift.
Behavioral design patterns Swift may be a set of methods like Template Method, Observer, Momento, Command, and others.
All three categories of software design patterns do carry some of their important methods, forms, and examples which we have not explained in the category itself. So, the following will be explaining them all in detail.
Swift Design Patterns Methods for iOS Apps
1 Singleton
The Singleton design pattern is about one instance for a given class with global accessibility. It uses lazy loading for creating one instance when required for the initial time. Now you would possibly be thinking what is the use of a single instance!
Well, there are chances and cases in which only makes sense with one example of a class.
For Example: UserDefaults.standard, UIScreen.main, UIApplication.shared, FileManager.default all restore in a Singleton object.
There are some cases during which it is sensible to possess exactly one instance of a class. For Instance, there’s only one instance of your application and one main screen for the device, so you only want one instance of each. Or, take a global configuration handler class: it’s easier to implement thread-safe access to a single shared resource, such as a configuration file, than to possess many classes modifying the configuration file possibly at an equivalent time.
The singleton pattern is simple to overuse. If you face a situation where you are persuaded to use a singleton, first consider other ways to achieve your task.
For example, singletons are inappropriate if you’re simply trying to pass information from one view controller to a different one. Instead, consider passing models via a property or initializer.
class NetworkManager {
// MARK: – Properties
static let shared = NetworkManager(baseURL: API.baseURL)
// MARK: –
let baseURL: URL
// Initialization
private init(baseURL: URL) {
self.baseURL = baseURL
}
}
Accessing the singleton is intuitive and it clearly conveys that we’re handling a singleton.
func application (_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
print(NetworkManager.shared)
return true}
Several execution details have changed. First, the initializer is private. It means only the NetworkManager class can create instances of itself. That’s a significant advantage.
Second, we announced the shared static constant property. This property gives other objects a gateway to the singleton object of the NetworkManager class.
2 Facade
Another representative of the iOS app design pattern Facade layout a single interface for complex subsystems. Regardless of its numerous methods with different interfaces, developers can create their own class to supply a simplified interface. ie, rather than exposing the user to a group of classes and their APIs, you only expose one simple unified API.
The facade is additionally useful when decomposing subsystems into different layers. The subsequent image explains this concept:
The design pattern is taken into account to be ideal for working with various classes, especially the complicated ones!
The user of the API is totally unaware of the complexity that lies beneath. The facade pattern is ideal when working with an outsized number of classes, particularly once they are complicated to use or difficult to understand.
This pattern decouples the code that put together use of the system from the interface and implementation of the classes you’re hiding; it also reduces dependencies of doors code on the inner workings of your subsystem. This is useful if the classes under the facade are likely to vary because the facade class can hold on to the same API while things change behind the scenes.
For example, if the day comes when you want to exchange your backend service, you won’t need to change the code that uses your API, just the code inside your Façade
class TreasureMapFinder {
enum Treasures {
case GALLEON; case BURIED_GOLD; case SUNKEN_JEWELS; }
struct MapLocation {
let gridLetter: Character; let gridNumber: UInt; }
func findTreasure(type:Treasures) -> MapLocation {
switch type {
case .GALLEON:
return MapLocation(gridLetter: “D”, gridNumber: 6);
case .BURIED_GOLD:
return MapLocation(gridLetter: “C”, gridNumber: 2);
case .SUNKEN_JEWELS:
return MapLocation(gridLetter: “F”, gridNumber: 12);
}
}
}
The TreasureMapFinder class defines the findTreasure method, which takes a value from the nested Treasures enumeration and gives back a MapLocation that represents the location at which the specified type of treasure can be found.
3 Model-View-Controller
Model View Controller also called MVC is one of the foremost used app architecture ios application design patterns in swift among others. It simply classifies objects as per the wants within the iOS application and ensures clean code separation against the role.
The 3 role that go with the mechanism is-
Model: Model is the first part of MVC that holds the application data and then defines how to manipulate it.
View: The second part of MVC is the object in- charge of the visual representation of the Model and controls user interaction with it.
Controller: The third and the last part of the MVC controller is the mediator between all the work. The controller accesses all the data from the model and then displays data with a view, manipulates it whenever required.
The overall communication between M-V-C is given below-
4 MVVM
Swift design patterns MVVM is one of the favorites among the iOS developers’ community. The View in MVVM consists of visual elements like animation, layout, UI components, etc.
Furthermore, the layer between the View and therefore the Model called ViewModel represents the view in a canonical way. Hence, the ViewModel thus supplies a group of interfaces and every interface then represents UI components within the view.
The Swift design patterns MVVM version thus assists when it comes to swift for developing iOS design patterns applications. The expert developers know the difference of when to use MVC or MVVM as per the need.
Model-View-ViewModel (MVVM) may be a UI architectural design pattern that decouples UI code from the business and presentation logic of an application. MVVM divides an application into three components to help separate the code: the model, the view, and therefore the view model. The View interprets the layout, appearance, and structure of the UI. The view notifies the ViewModel about user interactions and observables state changes exposed by the viewModel. The ViewModel is liable for wrapping the model and providing state to the UI components. It also defines actions which will be employed by the view to pass events to the model. However, it should not have access to the view. The Model describes core types and implements application business logic. It is totally independent of the view and view-model and reusable in many across the application.
5 Observer
The next design pattern is called the Observer design pattern, which defines a one-to-many dependency among objects. The dependency here means when one object changes state, its related dependents are going to be notified and updated, automatically.
An observer design pattern is also known as Publish and subscribe model where the subjects and observers are coupled loosely.
Here the communication takes place between observing and observed objects while removing the need to know about each other.
Cocoa makes use of observer pattern through Key-Value Observing (KVO) and notifications.
class ActivityLog : Observer {
func notify(user: String, success: Bool) {
println(“Auth request for (user). Success: (success)”);
}
func logActivity(activity:String) {
println(“Log: (activity)”);
}
}
class FileCache : Observer {
func notify(user: String, success: Bool) {
if (success) {
loadFiles(user);
}
}
func loadFiles(user:String) {
println(“Load files for (user)”);
}
}
class AttackMonitor : Observer {
func notify(user: String, success: Bool) {
monitorSuspiciousActivity = !success; }
var monitorSuspiciousActivity: Bool = false {
didSet { println(“Monitoring for attack: (monitorSuspiciousActivity)”);
}
}
}
6 Delegate
Delegation may be a design pattern that permits a class to hand off (or “delegate”) some of its duties to an instance of another class. That is in this pattern for iOS apps is meant for keeping implementation-specific behavior away from the generic class. You will require a delegate protocol, a delegator that delegates out the tasks and a delegate object that implements the delegate protocol and does the work that was requested by the “boss”.
First, we are defining a protocol that will encapsulate the responsibilities that we’re handing off. Like this:
protocol BakeryUpdationDelegate {
func cookieWasBaked(_ cookie: Cookie)
}
This BakeryDelegate protocol defines one function cookieWasBaked(_:). This delegate function will get to know whenever a cookie has been baked.
Second, we are including delegation into the Bakery class. Like this:
class BakeryUpdation
{
var delegate:BakeryUpdationDelegate?
func makeCookie()
{
var cookie = Cookie()
cookie.size = 6
cookie.hasChocolateChips = true
delegate?.cookieWasBaked(cookie)
}
}
Two things changed within the Bakery class:
The delegate property, of type BakeryUpdationDelegate, has been added
The function cookieWasBaked(_:) is named on the delegate in makeCookie(), with the delegate?.cookieWasBaked(cookie) code
That’s not all. Check this out:
The type of the delegate property is the protocol we specified earlier. You will assign any value to the delegate property, as long as it conforms to the BakeryUpdationDelegate protocol.
The delegate property is free, and we use optional chaining when calling that cookieWasBaked(_:) function. When the delegate is nil, the function isn’t called.
Third, let’s create the actual delegate class! Like this:
class CookieShop: BakeryDelegate
{
func cookieWasBaked(_ cookie: Cookie)
{
print(“Yay! A new cookie was baked, with size (cookie.size)”)
}
}
The CookieShop adopts the BakeryDelegate protocol and conforms to that protocol by implementing the cookieWasBaked(_:) function.
And finally, here’s how to set the code together:
let shop = CookieShop()
let bakery = Bakery()
bakery.delegate = shop
bakery.makeCookie()
// Output: Yay! A new cookie was baked, with size 6
Here’s what happens:
First, you create a CookieShop object and allocate it to the shop constant. Then, you create a Bakery object and allocate it to the bakery constant. Then, you assign shop to bakery.delegate. This makes the shop the delegate of the bakery.
Finally, when the bakery creates a cookie, that cookie is handed off to the shop, that can sell it to a happy customer. And that’s delegation! The bakery delegates selling cookies to the shop, and hands-off a cookie whenever it makes one.
7 Builder
Builder is used when required to develop complex objects from the simpler ones step by step. By using the same code, developers can produce different object views.
For instance- a complex object demands incremental initialization of nested objects and multiple fields. In such a situation, the initialization code might be concealed inside a mammoth constructor with parameters. Or possibilities are that the codes might be separate over the client code.
Now, to give a cure that too fast, the Builder design pattern separates the construction of an object from its own class.
The construction of objects is instead assigned to the builder and then divided into multiple steps.
There are a couple of steps which may assist you when applying a design pattern-
- When avoiding telescopic constructor.
- When code is required to make many views of a specific object.
- When there is a requirement for composing complex objects.
8 Command
Command design pattern encapsulates requests within the sort of objects and allows developers to explain or represent clients with several requests, log requests, queue, and support operations.
These requested objects then bind together into one or more actions on a selected receiver. Moving on, the command design pattern separates an object from making an invitation from another object for receiving or executing purposes.
9 Memento
The Memento pattern saves the data somewhere. Later, the externalized states are often restored without encapsulation violation. Encapsulation means private data will remain private with no threat of theft or loss. a couple of implementation samples of the Memento pattern is- Archiving, Serialization, and State Restoration.
10 Strategy
Strategy, subsequent swift architecture patterns for developing iOS apps allow developers to vary the algorithm behavior at run time. With the assistance of interfaces, one can define the family of algorithms while encapsulating and making them interchangeable. The practice allows one to pick an algorithm for executing them at run time.
11 Template
The template design pattern in Swift defines the general skeleton of the operational algorithm. Once done, the template method pattern then redefines the steps of an algorithm without making any become the algorithm’s structure.
12 Factory
For removing and adding new sorts of the codebase, the Factory method pattern gives smooth flexibility. To feature a replacement type, developers require a replacement sort of class alongside a replacement factory for producing codes.
13 Composite
Part of Model-View-Controller, the composite design pattern frames objects into a tree structure form for representing hierarchies. The tree-like structure helps out clients to treat individual objects and compositions of objects uniformly.
14 Iterator
The next Iterator swift architecture patterns give access to the element of an aggregate object without exposing underlying representation. Iterator pattern here transfers the responsibility of accessing and traversing the element from the gathering to an iterator object. Here, the iterator defines an interface for accessing the gathering of elements and further keeping track of the present element.
15 Mediator
How a class of objects interacts is what the Mediator design pattern defines. The pattern promotes loose coupling by keeping objecting from pertaining to one another. Thus, it lets developers see the interaction between them independently. Besides, these objects remain reusable for other requirements. The mediator object also centralized complex communication alongside controlling the logic between objects within the system. As a result, these mediator objects then provide information about when the thing changes while responding to the requests.
16 Proxy
Works as a surrogate or placeholder, another design pattern utilized in swift for developing an iOS app is Proxy. It manages access over objects as placeholders or surrogates. Developers can use Proxy design patterns in Swift for creating a proxy or representative of another object to realize access to a different object. These objects further are often expensive, remove or require a secure network. Though the pattern of Proxy design patterns in Swift is somewhat almost like a decorator pattern but serves a different purpose- proxy controls access to an object whereas decorator adds behavior to any object.
17 MVP
MVP or Model View Presenter may be a three-component design pattern- the Presenter (UIKit independent mediator), the Passive View (UIView and/or UIViewController), and therefore the Model. There is another MVP method used for mobile applications with limited and core features to trace what’s being liked or disliked by users. Meanwhile, here the MVP patterns for iOS define Views as Recipients of the UI events calling the acceptable presenter when required. The presenters indicate for updating the View with fresh data replaced by the Model. Also, the role of the presenter is supposed for binding the model to the view. Moreover, View is coupled loosely to the model.
18 Decorator design
Without modifying the code, subsequent design patterns in swift called the Decorator pattern adds behaviors and responsibilities to any object. it’s seen as an alternative to subclassing for modifying the class’s behavior by wrapping whole with another object.
19 Adaptor
The adapter design pattern needed for developing the iOS design pattern app turns the class interface into another interface as per the client requirements. This adaptor allows classes to work together while decoupling the client from the class of the thing targeted. Apple’s app store rules are a touch different and this is often the rationale, the tech giant uses protocols for work using Adapter.
Conclusion
Design patterns are a particularly important tool with which developers can manage complexity. It’s best to represent them as generally templated techniques, each custom made to solve a corresponding, recurring, and readily identifiable problem. Check out them as an inventory of best practices you’d use for coding scenarios that you simply see over and once again, like the way to create objects from a related family of objects without having to know all the gory implementation details of that family. The entire point of design patterns is that they apply to commonly occurring scenarios. They’re reusable because they’re generalized. Above mentioned are some common iOS architectural design patterns which you’ll use while developing your iOS application.
From the above-listed design patterns, MVC as an architecture provides sensible separation of concern however it always introduces the so-called concept of bloated ViewControllers. MVP and MVVM both eliminate the matter of bloated ViewControllers in MVC. So, they’re sensible architectural patterns.
An amalgamation of a compact language like Swift related with an arsenal of best practices, like design patterns, happens in an ideal and happy medium. Consistent code is usually readable and maintainable code. confine mind too that style patterns are ever-evolving as many developers are constantly discussing and sharing ideas. By virtue of being connected along over the world Wide Web, this developer discussion has led to constantly self-regulating collective intelligence.
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