Chapter 11: Easy Navigation with Coordinators

An iOS app is usually a collection of single screens somehow connected to each other. Inexperienced developers often present a view controller from another view controller, because this is easy to implement and it is often shown that way in tutorials and demo code. But, for apps that need to be maintained over a long period of time, we need a pattern that is easier to understand and easier to change.

The coordinator pattern is very easy to implement and still manages to decouple the navigation between views of the app from the presentation of the information. In the coordinator pattern, a structure called a coordinator is responsible for navigating between views. View controllers tell the coordinator that the user interacted with the app and the coordinator decides which view controller should become responsible for the screen next.

As a bonus, the coordinator pattern makes testing navigation code simpler and more robust, and as a...

Technical requirement

The source code for this chapter can be found here: https://github.com/PacktPublishing/Test-Driven-iOS-Development-with-Swift-Fourth-Edition/tree/main/chapter11.

Testing the app's setup

When our app starts, a coordinator should be instantiated and started. This should result in the presentation of the initial view of our app. Follow these steps to refactor the setup from using a storyboard to using a coordinator:

1. Before we can refactor the setup of the app, we need a test that tells us when we break something. Select the ToDoTests group in the project navigator and add a new Unit Test Case Class instance with the name AppSetupTests.
2. Replace the content of the new class with the following:

   // AppSetupTests.swift
   import XCTest
   @testable import ToDo
   class AppSetupTests: XCTestCase {
     func test_application_shouldSetupRoot() {
       let application = UIApplication.shared
       let scene = application.connectedScenes.first
       as? UIWindowScene
       let root =
         scene?.windows.first?.rootViewController
     ...

Navigating to the details

We will implement the navigation within the app using the AppCoordinator class. Follow these steps to implement navigation to the details of to-do items:

1. Add the following test method to AppCoordinatorTests:

   // AppCoordinatorTests.swift
   func test_selectToDoItem_pushesDetails() throws {
     let dummyViewController = UIViewController()
     let item = ToDoItem(title: "dummy title")
     sut.selectToDoItem(dummyViewController, item: item)
     let detail = try XCTUnwrap(
       navigationControllerMock.lastPushedViewController
       as? ToDoItemDetailsViewController)
     XCTAssertEqual(detail.toDoItem, item)
   }

In this test, we execute the delegate method and assert that an instance of ToDoItemDetailsViewController is pushed to the navigation stack, and that its toDoItem is the item we used in the delegate method call.

Run the tests to confirm that this new test...

Navigating to a modal view

Normally, testing the presentation of a modal view controller is quite complicated. If you search how to do that on the internet, you will find that the common solutions work by swizzling the present(_:animated:completion:) method defined in the UIViewController class. Swizzling is quite complicated, and I will not show in this book how this is done.

But, because we are using the coordinator pattern for the navigation in our app, we can test the presentation without the need to swizzle any method. Still, you should look up how to swizzle methods because sometimes you don't have the option to use the coordinator pattern; for example, when there is already all the navigation code implemented and you are not allowed to change it.

Follow these steps to implement the presentation of the input view when the user chooses to add a new to-do item:

1. The app needs a button in the user interface that the user can tap to add a to-do item. When the user...

Adding missing parts

First, let's run the app for the first time to see where we are.

The app starts with a blank screen with just one plus (+) button in the upper-right corner.

Figure 11.2 – The initial view of our app

So, there is work to do here. But, let's move on and tap the plus (+) button. We are presented with the input view. We can add data for the item and tap the Save button.

Figure 11.3 – The input view of our app

But, when we tap the Save button, nothing happens. Dismiss the view by swiping down, and see whether the item was added. Something changed. There is a blank table view cell visible in the middle of the screen.

Figure 11.4 – A blank table view cell. Where is the to-do item?

When you tap the blank table view cell, the detail view is pushed onto the screen.

Figure 11.5 – The details of the to-do item. But, where is the due date...

Summary

In this final chapter, we have implemented the navigation between the different views of our app. We have learned how to test pushing view controllers onto a navigation stack and how we can test whether a view got presented modally.

With navigation implemented, we started the app on the simulator and found and fixed bugs. We figured out that TDD even helps when fixing bugs. By writing first a failing test for that bug and then making the test pass, we ensured that this bug won't hurt us in the future of our app.

With the skills you gained in this chapter, you will be able to implement and test the navigation of an app using the coordinator pattern. And, you are now able to write tests for bugs and fix the bug by making the test pass.

Congratulations, you reached the end of this book! My hope is that this book is the beginning of your journey to becoming a test-driven developer. You learned how to test Combine code and write tests for view controllers and views...

Exercises

1. Fix the bugs you found while testing the app on the simulator.
2. Add the feature that the user can check to-do items in the list of all to-do items.
3. Write a review for this book on Amazon.

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