Tutorial: delegates and delegation in Swift 4

The original article – Understanding Delegates and Delegation in Swift 4 was published on appcoda.com.

[Download Xcode 9 project with full Swift 4 source from GitHub.]

Introduction

I’m going to talk about “delegates” and “delegation.” I’ll lead you through a simple example of implementing the delegation design pattern in Swift 4, with full source code. My intent here is to show you how delegation works without getting bogged down in some crazy complex example. To help you become the best of the best, I’m going to introduce you to one of the greatest design tools to aid in object-oriented software development, UML. I’ll show you a UML diagram that I drew up to design and document the implementation of the delegation design pattern used in the sample app we’ll build together. Download the Xcode 9 project with full Swift 4 source from GitHub to follow along.

(Note: compare this post’s approach of using delegation with my next post’s approach of using NSNotificationCenterto accomplish the same goal.)

I’ll show you how to build a user interface (UI) helper, a class that downloads a file at a specified URL. Most importantly, I’ll show you how, through delegation, a UIViewController subclass can be notified by the helper that an image file has finished downloading, and then the view controller can display the image on screen. For the sake of simplicity and clarity, we’ll pretend that Swift has minimal support for downloading a file from a URL. We’ll manually wire up the notification that the file has finished downloading using the delegation design pattern. Here’s the app we’ll build:

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Fix for IBOutlet, IBAction connections disappearing in Xcode 9

You’ve been working on your billion dollar app happily for days or weeks. It’s Monday morning, you open up Xcode 9 to get back to work and — dang, bummer — all your IBOutlet and IBAction connections look like they’ve been disconnected (see image below):

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Xcode tidbits: Open as Hex, Open As Source Code, (Git) line endings, and text encoding

With this article, I’m starting a series about all the goodies — useful tools — that can be found in Xcode. Some of these tidbits are tools everyone knows about while others are barely documented to undocumented. For example, how many of you know that you can view, inspect, and debug all your Auto Layout constraints live during app execution using the “Debug View Hierarchy” Xcode feature? I discussed that feature in detail in this article, “Troubleshooting Auto Layout using Xcode’s Debug View Hierarchy.” Today, we’ll discover two editors that ship with Xcode, the “Open As > Hex” and “Open As > Source Code” editors, both only available by right-clicking on files in the “Project Navigator” to reveal a contextual menu.

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Building Swift 4 frameworks and including them in your apps (Xcode 9)

Let’s talk about Swift 4 frameworks, one method for packaging, reusing, and sharing code. We’ll build our own framework and then include it in our own app. We could’ve talked about static libraries, but frameworks offer more advanced features — and will let us expand on code maintainability options in future discussions. (If you want to have that static versus dynamic library discussion, read this excellent article, but we won’t be debating the topic herein.) From Apple (my emphasis added):

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Typical Git/GitHub workflow tutorial: configure, clone, commit, stage, push, pull, status

Introduction

Suppose your supervisor or customer gives you a new project to work on: “I want you to start helping out on my iOS project, ‘Blocks-in-Objective-C.’ Please get a copy of the code, make these changes, test, and then check your new code into the repo. By the way, we’re using Git for source control.” Have you used Git before? Do you know it well? (Does anyone truly understand Git?) Today, I’ll show you how to accomplish that task just assigned by your supervisor or customer.

Requirements

Since this is an iOS blog, I’m assuming you’ve installed Xcode and therefore Git is installed on your Mac. (If you need to install Git, click here.)

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Swift 3, iOS 10, Xcode 8: finding, adding, and removing IBOutlets

I’m going to show you how you can create IBOutlets, find your existing ones, and delete them. There will be times when you need to delete outlets, for example, if you connected the wrong component, have to change your design, misspelled an outlet, etc. You can’t do iOS without doing IBOutlets. An outlet is a connection you must create to allow your user interface (UI) to communicate with your code. For example, if you have a UIView on a storyboard scene, like a UIViewController, you may want to change that view’s background color during app execution. You may also need the bounds or frame of the view. If you have a UIButton, you may want to dynamically enable or disable it depending on some runtime condition. Say you have two UITextFields, “username” and “password,” and a UIButton containing the text “Login.” With IBOutlets, you could write your code so that the login button’s isEnabled property becomes true only when the username and password fields are filled with data. You would also want the text contained in the username and password fields once the user taps “Login.” IBOutlets form a connection between UI components like UILabel, UITextField, and UIView and their backing view controller that manages their behavior and presentation.

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Creating a new Git/GitHub repository for your Xcode project — a detailed tutorial

Let’s talk about source/version control, why it’s so important, and how you can easily put all your iOS code under source/version control management (SCM). I’m going to show you the manual steps involved in putting your code into a Git SCM “repository” (repo) so you fully understand how source/version control works. Jump straight to the tutorial if you’re already familiar with the concept of source control. I can’t explain everything about SCM in one blog post, but I’ll get you started and provide many online resources for you to reference. Why am I using Git? Like it or not, Git has become the de facto standard in SCM systems, mainly because it “is a free and open source [and] distributed version control system.” I don’t buy into the “Git is easy to learn” argument. I find Git to be overly complicated, cryptic, and generally requiring more steps to accomplish source control tasks than say centralized SCM systems like TFS or Subversion/SVN. Git does have some advantages over other SCM products, and it even becomes quite efficacious once you pay your dues learning how to use it properly.

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UPDATE: Renaming an Xcode 8 project, the easy way or the advanced way

NOTE: This article was first published on Jan 18, 2017. Since that time, I realized I missed one aspect of the project renaming process. Re-read the article or jump straight to the new content.

Sometimes you need to rename your Xcode projects. Not too long ago, this would’ve been problematic. Apple has built a project renaming feature into Xcode, but it’s not good enough for my needs. I’ll show you how I have to go above and beyond the standard functionality to get what I really want. Let’s walk through a concrete example, renaming an Xcode project we’ve been talking about in the post entitled “The UICollectionView is much more than a grid or matrix”.

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Xcode secrets: save time with context-sensitive help and documentation

How many times have you been looking at Swift or Objective-C code in Xcode and can’t remember what a framework method, argument, constant, etc. means? Did you know that help — full documentation — is just a keystroke away? Did you also know that you can add the same type of pop-up, context-sensitive help to your own code? Here’s how. Let’s say you’re looking at the following NSString class method and can’t remember exactly what the call does, what parameters it takes, and what is its return value:

Highlight the method name, parameter, even the enum, and then press the following key combination on your keyboard:

[command] + [control] + [shift] + [?]

      or, using key symbols:

⌘ ⌃ ⇧ ?

Here’s what you’ll see: a context-sensitive help/documentation popup. Note that I added the red lines to highlight content. The red highlighting is not what Xcode provides (click to enlarge):

Figure 1: Xcode framework context sensitive help and documentation.

So you immediately get information about the method, parameter, enum, even constant’s:

  • Declaration (formal language signature);
  • Description (textual explanation of the entity’s purpose);
  • Parameters (a full list of names and definitions);
  • Returns (the value returned by a method/function, if applicable);
  • Availability (what version of iOS that the entity became available in — and sometimes in what version it was deprecated);
  • Declared In (the framework which contains the entity); and,
  • More (generally, the formal definition of the entity with explanations and other links).

Check out what I get if I click on the “More Type Method Reference” link as shown in Figure 1 (click to enlarge):

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Troubleshooting Auto Layout using Xcode’s Debug View Hierarchy

What’s more important when troubleshooting software, 1) what you intended in design or 2) what was materialized by running your code in a production environment? Take Auto Layout for example. Interface Builder may be happy with your constraints, displaying no warnings or errors, but when you run your app, you see problems. I find it much more helpful to see my all my Auto Layout live, while my app is running. I’ve found that using Xcode’s Debug View Hierarchy button is an often over-looked but extremely powerful tool for solving app layout problems, especially when iOS developers have to write app user interfaces that run on differently-sized devices in multiple orientations. The Debug View Hierarchy feature helps you understand how Auto Layout works. You can see all of your app’s:

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