SwiftUI

https://developer.apple.com/xcode/swiftui/

SwiftUI is the preferred way to write Swift apps on Apple devices.

Swift

See my note on Swift for more general Swift language notes.

Info.plist properties

Info.plist might not initially exist within a target folder when creating a project. Once you add an "Info" property, Xcode will make it on your behalf. To add an "Info property" navigate to the following: Project Settings > Targets > AppName > Info. If you hover over individual rows you will see +/- buttons that will add new rows and remove current rows. You can, e.g., go to the bottom row and click plus to add a new row. If this is the first time you do it you will generate a Info.plist file and add the property to it.

App uses non-exempt encryption property

https://developer.apple.com/documentation/security/complying-with-encryption-export-regulations

Here is an example navigation for an iOS app:

Project Settings > Targets > iOSAppName > Info > Custom iOS Target Properties. Create the property "App Uses Non-Exempt Encryption" and set it to "NO" (assuming you are building a basic app with no encryption, etc). The Info.plist file should contain something like the following afterwards.

<plist version="1.0">
<dict>
	<key>ITSAppUsesNonExemptEncryption</key>
	<false/>
</dict>
</plist>

Deploy to TestFlight early and often

This is true of every platform, but I feel like for Swift it is particularly valuable because of the complexity of working with XCode and it's configuration files. Having commits of known successfully deploys to TestFlight become crucial 'save points' for future work, allowing you to see diffs of settings files that you didn't know you would have changed otherwise.

You might find it more difficult than you initially expected to get a hello world app from TestFlight onto your devices!

https://developer.apple.com/documentation/xcode/preparing-your-app-for-distribution

Here are some of my historical failures:

• I didn't have AppIcons uploaded and it would fail the XCode Cloud build with an esoteric error. I finally fixed it by doing a 'local archive' and manually distributing it to AppStoreConnect. The errors I got back from that process were what informed me that my lack of icons was causing the error.
• I didn't (and still don't, really) understand the relationship between a watchOS target and it's companion iOS target and messed up my AppStoreConnect apps and bundle ids. It seems that the watchOS app is associated with the primary target as "embedded content" (Settings > Targets > (Primary iOS target) > General > Frameworks, Libraries, and Embedded Content)
• I wouldn't start with extra options enabled because they mess up the build pipelines. I recommend starting new projects with no storage options and no testing frameworks. I recommend new projects create targets per platform and not use the "multiplatform" option. I recommend all this because I want to get to a "hello, world" git commit that has been deployed all the way to test flight on every platform you currently support. This is the save point from which it feels safe to start modifying (often on accident!) configuration files.

gitignore for Swift Apple Xcode etc

As of this writing if you create a new Xcode project and tick the box to create a git repository for you, it will create a first commit that includes folders you want to ignore. So don't tick that box and create it manually via git init.

https://github.com/github/gitignore/blob/main/Swift.gitignore https://github.com/github/gitignore/blob/main/Global/Xcode.gitignore

Based on these links and previous investigations I'm hazy on, it seems this might be the only required line to gitignore:

xcuserdata/

This appears in AppName.xcodeproj/xcuserdata/, which looks like it ultimately contains a property list of what appear to be local settings for my IDE etc.

Observable Protocol vs Macro

If you want a class to be observable do not have that class extend the protocol.

// BAD
class Env: Observable {}

It needs to be tagged with the macro so that the macro can add the required functionality for observation via meta-programming.

// GOOD
@Observable
class Env {}

SF Symbols

SF Symbols is Apple's icon kit. In SwiftUI you use them via the Image struct. I forget how exactly I downloaded the SF Symbols application, but it's an app you can open on your computer and peruse to see the different system names.

Image(systemName: "scribble")

XCode Previews and Simulators

File storage in XCode previews, simulators, etc

The preview is what is within XCode. Running a simulator will actually open up the "Simulator" app. Previews are placed in some kind of sandbox that cycles on every preview render. I could see that something was being preserved in the directory I cared about, but it was essentially being wiped on each re-render of the preview. This was not the case for the simulator. It will preserve state changes made to the device, even beyond what I was expecting, e.g., other apps were still on the simulated device (you can wipe it if you want).

XCode Simulator display scaling and positioning issues

I have a problem where the initial iPhone simulators have a large gap between the top of the iPhone simulation and the menu bar for the simulation. This pushed the bottom of the iPhone simulation off the bottom of my computer screen.

The fix for this is in the "Window" drop down menu. For example "Window > Physical Size" with both fix the gap problem I have and resize the whole simulation smaller (at least on my machine). It also has a hotkey "cmd+1". There are a few other hotkey'd scaling options as well.

return from a preview macro

If you are like me the preview macro is one of the first places you run into a trailing closure with an implicit return.

#Preview {
    YourView()
}

If you want to instantiate some entities to pass in to that preview, your preview will break unless you return from it. This is because the initial preview used an implicit return since it was a single line.

#Preview {
    let note = Note(content: "some content")
    return YourView(note: note)
}

Previews with custom data

There are development assets you can declare which aren't included in final builds. There is WWDC sample code using a pattern of extending a class in the Preview\ Content/ folder which is declared a development asset. But using that sample data in the #Preview macro will cause an archive failure because the archive cannot find the extensions that defined the sample data, since they are a development asset. There is an 2020 stackoverflow post about this issue that is unresolved and I have commented on. The work around that seems to be the most common is wrapping #Preview macros in #if DEBUG ... #endif flags. This is only necessary when you reference development asset data. If you hard code the data within the previews, or define the sample data extensions outside of the development assets, then presumably you can archive successfully.

SwiftUI onDelete

This article, Deleting items using onDelete does a good job at explaining some of the quirks of the .onDelete function, like why you have to use a List and a ForEach. Another quirk is that the provided data to the action: param is an IndexSet, which is a set of integers from the ForEach array that are 'to be deleted'.

Recording audio

https://www.hackingwithswift.com/example-code/media/how-to-record-audio-using-avaudiorecorder

I had to do a lot of trial and error and reading docs and experimenting before I finally got audio record plus playback working. It worked in the preview macro, on the simulator, and cast to a local device.

The biggest piece that was missing for me was AudioSession. You have to set it to some version of record. Here is a snippet of my AudioRecorder class.

@Observable
class AudioRecorder {
    init() {
        let dir = FileManager.default.temporaryDirectory
        let file = UUID().uuidString + ".m4a"
        let filepath = dir.appendingPathComponent(file)
        self.audioUrl = filepath

        let audioSession = AVAudioSession.sharedInstance()
        do {
            try audioSession.setCategory(.playAndRecord, mode: .default, options: .defaultToSpeaker)
            try audioSession.setActive(true)

            let recorder = try AVAudioRecorder(url: self.audioUrl, settings: [ AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue ])
            recorder.prepareToRecord()

            self.recorder = recorder
        } catch {
            print("Failed to initialize recorder and/or audio session: \(error.localizedDescription)")
        }
    }
}

Streaming audio and video

https://developer.apple.com/documentation/avfoundation/avplayer

import AVFoundation

@Observable
class AudioPlayer {
    private var player: AVPlayer
    private var isPlaying = false

    init(url: URL) {
        let playerItem = AVPlayerItem(url: url)
        self.player = AVPlayer(playerItem: playerItem)
    }

    func toggle() {
        if (isPlaying) {
            player.pause()
            self.isPlaying = false
        } else {
            player.play()
            self.isPlaying = true
        }
    }
}

URLSession: probably use a default session and not a shared session

From the Foundation / URLSession / shared documentation:

SwiftData

https://developer.apple.com/documentation/swiftdata

SwiftData and the Preview macro

This is a subtle thing that can cause a lot of frustration. A lot of work is done on your behalf, and if you get that automagic instantiations out of order, things don't render in preview. This article on How to use SwiftData in SwiftUI Previews helped me better understand what I was doing wrong.

Many-to-many relationship are a fickle beast as well. Easy to get this stuff wrong and stare at full on system crashes for hours. For many-to-many relationship you cannot forget to insert via container.mainContext.insert or else the associations won't persist, and reading 'through' the associations won't work in the test setup. See this article on How to create many-to-many reationships, also by Hacking with Swift, which is quick becoming a favored resource of mine.

SwiftData seems designed for interacting with internet databases?

https://developer.apple.com/documentation/SwiftData

The sample code from Maintaining a local copy of server data is the best holistic example of how to leverage SwiftData as a cache of remote data.

SwiftData .modelContainer

You only need one .modelContainer for an entire view hierarchy. If you add more later down in the view hierarchy, that will be a different container. Views attached to the original .modelContainer will not see the other container's data.