Swift Coordinator Pattern: Step-by-Step Guide for iOS App Development

Swift Coordinator Pattern:

Step-by-Step Guide

for iOS App Development

By Ronald Tuch

By Ronald Tuch

Swift coordinator pattern

The Coordinator pattern in Swift is a powerful structural design pattern. It’ll help organize your mobile app’s navigation flow and simplify its architecture.

In this step-by-step guide, we’ll explain why you should use the pattern and how you can implement it in your next project.

Ready to elevate your iOS game? Let’s dive right in!

What is the Swift Coordinator Pattern?

The Coordinator pattern in Swift is a structural design pattern that organizes the data flow between different parts of a mobile app. It acts as a control center, managing the navigation between Views and Controllers.

You can use this pattern only in one part of the app or to define the complete structure of your mobile application. The main goal here is to manage the Views’ behavior. And don’t forget that one Coordinator can call another Coordinator in the app.

Need an example? For instance, your coordinator handles the app’s flow from the first screen when the app starts. Each of your view controllers will then communicate with the exact coordinator whose interface component the user engages. At this point, the coordinator will tell the app which view it should open next.

Why Use the Swift Coordinator Pattern for iOS Development?

here are several reasons why you should use the Swift coordinator pattern for iOS development.

One of the most common problems developers in the iOS community face is with big view controllers. These controllers usually combine the mobile application’s data flow, view logic, and business logic.

However, this complicates things unnecessarily.

How so?

Encoding the app flow logic into the controller directly prevents reuse without copying the whole code.

In other words, as the mobile application grows and you add more views to it, you’ll end up duplicating the source code of all view controllers in order to navigate between the views.

So, how can you handle this problem? You can use the Coordinator design pattern to divide the navigation logic and create a clear navigation flow. As a result, the view controllers can focus on their core responsibilities.

This approach allows you to reuse a view controller without copying its code. The best part is that in larger iOS apps, you can even include sub-coordinators to create hierarchies in your application flow.

How to Get Started with the Swift iOS Coordinator Pattern?

Now that you know why you should use Coordinator patterns, let’s examine how to start using them in Swift.

The Coordinator design pattern lets you code a Swift app with a flexible, modular, and easy-to-scale architecture. You’ll need previous knowledge of Swift. It will also help if you’re familiar with design patterns, MVVM, and MVC architectures. You’ll also need to be able to set up Xcode and use SwiftUI or UIKit to develop your iOS mobile application.

Next, we have the steps you need for Coordinator patterns to handle the flow logic of your apps.

Step-by-Step Guide to Using the Swift Coordinator Pattern

Follow these steps for proper iOS app development using the swift coordinator pattern.

In this section, we’ll walk you through the required steps to implement Coordinator patterns in Swift. From creating the default implementation of the base coordinator, through setting up the coordinator hierarchy, to navigating through views and handling dependencies, let’s dive right in:

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Step 1. Create the Base Coordinator

The base coordinator is the core of the design. It orchestrates the navigation within the mobile app, defines the behavior of the view controller transactions, and serves as a template for all other coordinators.

Include the main methods to be inherited and customized by the coordinator subclasses in the base coordinator. The most common method is start(). It’s the entry point for each coordinator and initiates its specific navigation flow.

Subclasses can override the start() method by raising a fatalError. This guarantees consistency across coordinators.

The base coordinator usually includes a finish() method as well. It’s responsible for the cleanup and final tasks at the end of the navigation flow. The same method allows for graceful termination of the coordinator instances. This helps memory management and resource allocation.

Step 2. Implement a Concrete Coordinator

After implementing the base coordinator, you need to code the concrete coordinator. Its job is to handle specific navigation flows and features of the mobile app. Concrete coordinators extend the base coordinator’s behavior. They allow customization of the navigation and specific requirements for each flow.

Implementing concrete coordinators is key to adopting the Coordinator in Swift. It enables developers to structure navigation flows in a clear and organized way, and customizing the navigation logic within each coordinator makes apps more stable.

The concrete coordinator overrides the base coordinator’s inherited start() method. This method starts the navigation logic and allows the concrete coordinator to manage the presentation and transition of view controllers.

This modular approach helps with several things, such as code reuse, testing, and control over the mobile app’s navigation behavior.

Step 3. Set Up Child Coordinators

In addition to the base and concrete coordinators, the Coordinator offers even more flexibility by organizing navigation flows in a hierarchy. This is achieved by setting up child coordinators, also called subcoordinators.

A child coordinator is an instance of the coordinator class managed by a parent coordinator. This enables the delegation of responsibilities and the handling of complex navigation flows.

To set up a child coordinator, the parent coordinator uses arrays or collections to store the references to its child coordinator instances. Parent coordinators initiate and start child coordinators and pass any necessary dependencies. To manage child view controllers, use a navigation controller. A navigation controller is a container view controller that stores child controllers in a navigation interface.

This hierarchy allows the management of navigation flows at different granularity levels. The approach promotes modularity and encapsulation. Each child coordinator is responsible for a specific subset of tasks.

This creates a clear separation of concerns and helps maintenance. Child coordinators also help with reusability since once they’re composed, they can be reused across different parts of the iOS application.

Step 4. Connect Coordinators to Initial View Controller

concept of connecting coordinators to initial view controllers

After you’ve set up the base and concrete coordinators, you need to connect the root coordinator to the mobile app’s initial view controller. This connection is established at the application’s entry point. The root view controller is the first view controller on the application stack.

The connection between the coordinators and the root view controller is usually achieved by AppDelegate in single-window apps and SceneDelegate in multi-window apps. The method creates the root view controller and associates it with the root coordinator. This guarantees the navigation flow will start from the correct point and ensures the navigation hierarchy is properly established from the beginning.

Connecting the root coordinator to the root view controller creates a central point of navigation control within the app. This helps the clear separation of concerns and promotes modularity.

This step is critical for implementing the Coordinator. It’s important not to skip it as it helps with effective navigation management and proper organization in your iOS app.

Step 5. Navigate Between Screens

Now that you‘ve connected the coordinators to the initial view controller, the next step is to implement methods for the navigation between screens and view controllers.

These methods define the sequence of actions for transitioning from one screen to another. They include presenting, pushing, and transitioning between view controllers.

According to the app’s navigation flow, you need to define specific navigation methods within each concrete coordinator. They’ll describe the logic for displaying and transitioning the appropriate view controller. The methods will trigger based on user interactions or changes in the state of the app.

This step is important for enabling the management of navigation flows in different parts of the app and enhancing the user experience.

Step 6. Handle Dependencies

Effective dependency management is essential for mobile apps. You need to properly implement this step. This way, coordinators will remain decoupled from other application components. On top of that, they’ll have access to the resources they need to perform their tasks.

Dependencies can include services, data models, view models, or other objects. All these, the coordinators need to navigate and coordinate interactions between view controllers. This depends on your app’s requirements.

There are several approaches for handling dependencies within coordinators:

  • Initializer injection: You pass dependencies to coordinators in their initializers. This allows explicit declaration of dependencies and makes the coordinators self-contained and independent.
  • Property injection: You provide dependencies to coordinators through properties. This enables flexibility in setting dependencies after a coordinator is initialized. It’s useful when you expect dependencies to change during the lifecycle of the coordinator.
  • Dependency containers or injection frameworks: This approach simplifies the configuration of dependencies in the iOS app.

Step 7. Integrate with Tab Bars and Navigation Controllers

The next step involves integrating coordinators with UI components like tab bar controllers and navigation controllers. These components provide standard interfaces for navigating between parts of the app, and coordinators need to integrate with them to manage the navigation flow.

Integrating with tab bar controllers lets coordinators manage tab-based navigation in apps with multiple top-level navigation paths. You can associate each tab with a coordinator that manages its respective navigation flow.

Integrating with navigation controllers allows coordinators to command navigation stacks and present view controllers. Usually, coordinators keep a reference to the navigation controller they’re associated with. The navigation controller stores child view controllers. The coordinators use the reference to the navigation controller push, pop, or display view controllers.

Step 8. Add Transition Animations

transition animations enhance the user experience and provide feedback.

Transition animations enhance the user experience. They provide visual feedback during navigation between different screens and view controllers. If you add transition animations to your navigation flow, they will create a smoother and more engaging main interface. It’ll also improve the usability of your mobile app.

A simple example of transition animations is presenting, pushing, or transitioning between view controllers.

Both SwiftUI and UIkit provide different built-in transition animations. Coordinators can use animation effects such as sliding, flipping, fading in, and fading out. The built-in methods for transition animations require parameters like duration, options, and completion.

When you add transition animations to your navigation flows, you create an immersive and visually pleasing user experience, which enhances the quality of your iOS app.

However, remember that animations require extra resources. You need to balance visual appeal and good performance, which is especially important on older devices.

Step 9. Deal with Common Navigation Scenarios

It’s important to handle common navigation scenarios effectively and consistently in mobile apps. This will guarantee a smooth and intuitive user experience. The scenarios include both user interactions and system events. They need coordinated navigation between different screens or view controllers in your app.

Here are some common navigation scenarios and how you can handle them:

  • Presenting modally. For this action, coordinators can use a method such as present(_:animated:completion:). The view controller provides it. This scenario happens when you need to present transient or context-specific screens. For example, such screens are login windows or settings panels.
  • Dismissing view controllers. Coordinators usually dismiss a view controller by calling dismiss(animated:completion:). This action is executed directly on the presenting view controller, or the task is delegated to subcoordinators.
  • Popping view controllers. Coordinators can pop a view controller off the navigation stack using methods like popViewController(animated:). This scenario is used when navigating back to a previous screen in a hierarchical navigation flow.

Step 10. Test Coordinator Logic

Only by testing the coordinator logic can you guarantee the reliability and proper functioning of your iOS mobile app. Perform unit tests to verify that navigation flows behave as expected. Also, check that they handle edge cases properly and maintain consistent behavior in different parts of the app.

Thoroughly testing the coordinator logic will let you find and address potential issues early in the development process. This will guarantee the high quality and reliability of your iOS app. Testing helps you validate the navigation logic, ensure its correctness, and deliver a robust and user-friendly product.

On top of that, unit tests serve as documentation of the coordinator’s intended behavior. This helps understand and maintain the source code later on.

Here are several types of unit tests that you need to add to your process:

  • Unit testing methods. Validate the behavior of individual methods of your coordinators. Test scenarios such as starting the navigation flows, presenting view controllers, pushing onto the navigation stack, and dismissing view controllers.
  • Integration testing navigation flows. Perform integration tests to validate the end-to-end behavior of navigation flows and how coordinators manage them. Simulate user interactions and verify the expected sequence of view controller transitions.
  • Edge case testing. Test coordinators under various edge cases and boundary conditions. This will ensure the app’s robustness. Consider scenarios such as handling empty data sets, invalid inputs, or unexpected system errors and events.

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Advanced Coordinator Pattern Usage

advanced coordinator pattern usage

When you use the Coordinator, you should properly define the scope of the functionality of the view controllers. This pattern makes it very convenient to swap the order of things or add special case screens to the flow, especially when working on large apps.

Projects with complex navigation, using, for example, nested screens and presenting modal dialogs with custom transitions, need to handle dependencies and pass data between the view controllers.

As the scope of your app grows, make sure to define the functionality of the coordinators and view controllers carefully. Handling complex navigation flows can get difficult if you don’t consider the following:

  • Use subcoordinators to reduce complexity. You can handle subflows with the help of subcoordinators in your iOS app design. This will add flexibility to your organization.
  • Manage dependencies effectively. Decouple coordinators from other application components. Use injections and dependency containers to simplify the configuration.
  • Pass data between view controllers. Use arrays and collections to represent the navigation stack. Use it to manage the navigation flow and pass data between view controllers.
  • Handle segues properly. Segues define the transition between view controllers in your app’s storyboard. Use the storyboard identifier to reference the correct view controller and its segues.
  • Use protocols in place of types. The coordinator protocol defines the methods and properties all concrete coordinators must implement. Protocols describe behavior rather than specific types, which makes the app more flexible and robust.

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Swift Coordinator Pattern FAQ

What is the difference between the Router and Coordinator patterns?

The two patterns have a similar goal – to separate the navigation logic from the views. They also make the app more modular, maintainable, and scalable. The main difference is that the Router manages the communication from a single-view controller. On the other hand, the Coordinator is responsible for the entire navigation flow.

What are the benefits of the Coordinator design pattern?

The Coordinator design pattern lets you code iOS apps with flexible architectures that are modular and easy to scale. It creates a clear separation of concerns and promotes modularity. Also, the source code is reusable and easy to maintain.

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