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Design Patterns by Tutorials

Third Edition · iOS 13 · Swift 5 · Xcode 11

Before You Begin

Section 0: 4 chapters
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Section I: Hello, Design Patterns!

Section 1: 2 chapters
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Section II: Fundamental Design Patterns

Section 2: 7 chapters
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Section III: Intermediate Design Patterns

Section 3: 8 chapters
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Section IV: Advanced Design Patterns

Section 4: 7 chapters
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9. Builder Pattern
Written by Joshua Greene

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The builder pattern allows you to create complex objects by providing inputs step-by-step, instead of requiring all inputs upfront via an initializer. This pattern involves three main types:

  1. The director accepts inputs and coordinates with the builder. This is usually a view controller or a helper class that’s used by a view controller.

  2. The product is the complex object to be created. This can be either a struct or a class, depending on desired reference semantics. It’s usually a model, but it can be any type depending on your use case.

  3. The builder accepts step-by-step inputs and handles the creation of the product. This is often a class, so it can be reused by reference.

When should you use it?

Use the builder pattern when you want to create a complex object using a series of steps.

This pattern works especially well when a product requires multiple inputs. The builder abstracts how these inputs are used to create the product, and it accepts them in whatever order the director wants to provide them.

For example, you can use this pattern to implement a “hamburger builder.” The product could be a hamburger model, which has inputs such as meat selection, toppings and sauces. The director could be an employee object, which knows how to build hamburgers, or it could be a view controller that accepts inputs from the user.

The “hamburger builder” can thereby accept meat selection, toppings and sauces in any order and create a hamburger upon request.

Playground example

Open FundamentalDesignPattern.xcworkspace in the Starter directory, or continue from your own playground workspace from the last chapter, and then open the Overview page.

What should you be careful about?

The builder pattern works best for creating complex products that require multiple inputs using a series of steps. If your product doesn’t have several inputs or can’t be created step by step, the builder pattern may be more trouble than it’s worth.

Tutorial project

You’ll continue the RabbleWabble app from the previous chapter. Specifically, you’ll add the capability to create a new QuestionGroup using the builder pattern.

Implementing the builder pattern

CreateQuestionGroupViewController is a new file added in this chapter. It uses a table view to accept inputs for creating a QuestionGroup. It displays CreateQuestionGroupTitleCell and CreateQuestionCell to collect input from the user.

Key points

You learned the builder pattern in this chapter. Here are its key points:

Where to go from here?

RabbleWabble has really come a long way since you created it, but there’s still a lot of functionality you can add.

8. Observer Pattern
10. Model-View-ViewModel Pattern
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