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UIKit Apprentice

Third Edition · iOS 18 · Swift 5.10 · Xcode 16

Before You Begin

Section 0: 5 chapters
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Getting Started

Section 1: 8 chapters
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Checklists

Section 2: 12 chapters
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My Locations

Section 3: 11 chapters
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Store Search

Section 4: 13 chapters
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34. Networking
Written by Fahim Farook

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Now that the preliminaries are out of the way, you can finally get to the good stuff: adding networking to the app so that you can download actual data from the iTunes Store!

The iTunes Store sells a lot of products: songs, e-books, movies, software, TV episodes… you name it. You can sign up as an affiliate and earn a commission on each sale that happens because you recommended a product — it can be even your own apps!

To make it easier for affiliates to find products, Apple made available a web service that queries the iTunes store. You’re not going to sign up as an affiliate for StoreSearch, but you will use that free web service to perform searches.

In this chapter you will learn the following:

  • Query the iTunes web service: An introduction to web services and the specifics about querying Apple’s iTunes Store web service.
  • Send an HTTP request: How to create a proper URL for querying a web service and how to send a request to the server.
  • Parse JSON: How to make sense of the JSON information sent back from the server and convert that to objects with properties that can be used in your app.
  • Sort the search results: Explore different ways to sort the search results alphabetically so as to write the most concise and compact code.

Query the iTunes web service

So what is a web service? Your app — also known as the “client” — will send a message over the network to the iTunes store — the “server” — using the HTTP protocol.

Because the iPhone can be connected to different types of networks — Wi-Fi or a cellular network such as LTE, 3G, or GPRS — the app has to “speak” a variety of networking protocols to communicate with other computers on the Internet.

App HTTP request GET http://itunes.apple.com/... JSON results HTTP request JSON results  { “resultCount” : 50, ... } iTunes Server
The HTTP requests fly over the network

Fortunately you don’t have to worry about any of that as the iPhone firmware will take care of this complicated process. All you need to know is that you’re using HTTP.

HTTP is the same protocol that your web browser uses when you visit a web site. In fact, you can play with the iTunes web service using a web browser. That’s a great way to figure out how this web service works.

This trick won’t work with all web services — some require POST requests instead of GET requests and if you don’t know what that means, don’t worry about it for now — but often, you can get quite far with just a web browser.

Open your favorite web browser — I’m using Safari — and go to the following URL:

http://itunes.apple.com/search?term=metallica

The browser will download a file. If you open the file in a text editor, it should contain something like this:

{
 "resultCount":50,
 "results": [
{"wrapperType":"track", "kind":"song", "artistId":3996865, "collectionId":579372950, "trackId":579373079, "artistName":"Metallica", "collectionName":"Metallica", "trackName":"Enter Sandman", "collectionCensoredName":"Metallica", "trackCensoredName":"Enter Sandman", "artistViewUrl":"https://itunes.apple.com/us/artist/metallica/id3996865?uo=4", "collectionViewUrl":"https://itunes.apple.com/us/album/enter-sandman/id579372950?i=579373079&uo=4", "trackViewUrl":"https://itunes.apple.com/us/album/enter-sandman/id579372950?i=579373079&uo=4", "previewUrl":"http://a38.phobos.apple.com/us/r30/Music7/v4/bd/fd/e4/bdfde4e4-5407-9bb0-e632-edbf079bed21/mzaf_907706799096684396.plus.aac.p.m4a", "artworkUrl30":"http://is1.mzstatic.com/image/thumb/Music/v4/0b/9c/d2/0b9cd2e7-6e76-8912-0357-14780cc2616a/source/30x30bb.jpg", "artworkUrl60":"http://is1.mzstatic.com/image/thumb/Music/v4/0b/9c/d2/0b9cd2e7-6e76-8912-0357-14780cc2616a/source/60x60bb.jpg", "artworkUrl100":"http://is1.mzstatic.com/image/thumb/Music/v4/0b/9c/d2/0b9cd2e7-6e76-8912-0357-14780cc2616a/source/100x100bb.jpg", "collectionPrice":9.99, "trackPrice":1.29, "releaseDate":"1991-07-29T07:00:00Z", "collectionExplicitness":"notExplicit", "trackExplicitness":"notExplicit", "discCount":1, "discNumber":1, "trackCount":12, "trackNumber":1, "trackTimeMillis":331560, "country":"USA", "currency":"USD", "primaryGenreName":"Metal", "isStreamable":true},
. . .

Those are the search results that the iTunes web service gives you. The data is in a format named JSON, which stands for JavaScript Object Notation.

JSON

JSON is commonly used to send structured data back-and-forth between servers and clients, i.e. apps. Another data format that you may have heard of is XML, but that’s being fast replaced by JSON.

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The HTTP request

Back to the original HTTP request. You made the web browser go to the following URL:

Synchronous networking = bad

Before we begin though, there is a good way to do networking in your apps and a bad way.

Send an HTTP(S) request

In order to query the iTunes Store web service, the very first thing you must do is send an HTTP request to the iTunes server. This involves several steps such as creating a URL with the correct search parameters, sending the request to the server, getting a response back etc.

Create the URL for the request

➤ Add a new method to SearchViewController.swift:

Perform the search request

Now that you have a valid URL object, you can do some actual networking!

Parse JSON

Now that you have managed to download a chunk of JSON data from the server, what do you do with it?

An overview of the JSON data

The JSON from the iTunes store roughly looks like this:

Nujneorehg Zefxuoxoxm Ugrum (baroqdj) bopeksBuurx: 48 jpso: “xomw” elpogmUp: 0877916 sjicyTeqa: “Oklow Qimgcox” Kikkiivibr ... sjxa: “namf” uvbintUm: 8382964 khiwrVebo: “Febwipd Irva Nayxecv”
Hco jdwekzofa in fco CGOJ nexa

JSON or XML?

JSON is not the only structured data format out there. XML, which stands for EXtensible Markup Language, is a slightly more formal standard. Both formats serve the same purpose, but they look a bit different. If the iTunes store returned its results as XML, the output would look more like this:

Prepare to parse JSON data

In the past, if you wanted to parse JSON, it used to be necessary to include a third-party framework into your apps, or to manually walk through the data structure using the built-in iOS JSON parser. But as of Swift 4, there’s a new way to do things — your old pal Codable.

Parse the JSON data

You will be using the JSONDecoder class, appropriately enough, to parse JSON data. Only trouble is, JSONDecoder needs its input to be a Data object. You currently have the JSON response from the server as a String.

Assumptions cause trouble

When you write apps that talk to other computers on the Internet, one thing to keep in mind is that your conversational partners may not always say the things you expect them to say.

Print object contents

➤ Modify the SearchResult class in SearchResult.swift to conform to the CustomStringConvertible protocol:

Error handling

Let’s add an alert to handle potential errors. It’s inevitable that something goes wrong somewhere and it’s best to be prepared.

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Work with the JSON results

So far you’ve managed to send a request to the iTunes web service and you parsed the JSON data into an array of SearchResult objects. However, we are not quite done.

Always check the documentation

But first, if you were wondering how I knew how to interpret the data from the iTunes web service, or even how to set up the URLs to use the service in the first place, then you should realize there is no way you can be expected to use a web service if there is no documentation.

Load more properties

The current SearchResult class only has a few properties. As you’ve seen, the iTunes store returns a lot more information than that, so you’ll need to add a few new properties.

Support better property names

➤ Replace the following lines of code in SearchResult.swift:

Use the results

With these latest changes, searchBarSearchButtonClicked(_:) retrieves an array of SearchResult objects populated with useful information, but you’re not doing anything with that array yet.

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Differing data structures

Remember how I said that some items, such as audiobooks have different data structures? Let’s talk about that a bit more in detail…

Show the product type

The search results may include podcasts, songs, or other related products. It would be useful to make the table view display what type of product it is showing.

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Sort the search results

It’d be nice to sort the search results alphabetically. That’s actually quite easy. A Swift Array already has a method to sort itself. All you have to do is tell it what to sort on.

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Improve the sorting code

➤ Change the sorting code you just added to:

33. Custom Table Cells
35. Asynchronous Networking
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