Weblog entries 2022

2022-12-12 When to use StateObject wrappedValue initializer

UPDATE 2023-04-28: Apple updated its documentation: https://developer.apple.com/documentation/swiftui/stateobject#Initialize-state-objects-using-external-data

On our team, we recently discussed the use of StateObject in SwiftUI. It's very useful for ViewModels. However you often want to initialize such a ViewModel with one or more parameters and you bump into the following bit of documentation:

"You don't call this initializer directly. Instead, declare a property with the @StateObject attribute in a View, App, or Scene, and provide an initial value"

Source: developer.apple.com

We were not the only ones struggling with this; see also this blog post by Sarun W, where they share a Slack screenshot quoting an Apple engineer saying that this initializer is supported.

Still, using that initializer means that if your view gets recreated, you lose all state since the ViewModel is destroyed and created as well. This is especially harrowing when you do network actions within the ViewModel.

Our conclusion is that StateObject(wrappedValue:) can be used at points in your app where you start a completely new flow. For instance in a popup where you create a screen with a NavigationView or NavigationStack. Otherwise, initialize elsewhere and use @EnvironmentObject.

2022-11-18 Example of hierarchical list

I actually didn't know that the SwiftUI List element natively supports hierarchical lists, until someone on Reddit asked for an example. Here's mine:

    struct Park: Identifiable {
        let id = UUID()
        let name: String
        let children: [Park]?
    struct ContentView: View {
        private let parks = [
            Park(name: "Sierra Nevada", children: [
                Park(name: "Yosemite", children: [
                    Park(name: "Mount Dana", children: nil),
                    Park(name: "Mount Lyell", children: nil),
                Park(name: "Stanislaus National Forest", children: [
                    Park(name: "Emigrant Wilderniss", children: nil),
                    Park(name: "Carson-Iceberg Wilderniss", children: nil),
        var body: some View {
            List(parks, children: \.children, rowContent: { Text($0.name) })

2022-09-15 Xcode linker error ld framework not found

Today I got the following error when trying to build my unittest for my Swift package:

  ld: framework not found CoreAPIKit

Note that the name of that particular framework (CoreAPIKit) doesn't matter; it's a framework that's only used internally at my client. Now on to the solution... In Xcode, we selected the project, and selected the unittest target, then selected the Build Phases tab. In that tab, there's the Link Binary With Libraries setting.

That setting listed "CoreAPIKit.framework"! So, why does this go wrong?

We removed that framework, then added it again. This time, it was saying "CoreAPIKit" (i.e. without the extension). Now, the unittest target correctly linked.

2022-09-14 Getting an unescaped JSON string from Xcode console

If you're debugging an app, you may want to copy raw JSON in Xcode, then paste it into a specialized app. The problem is, Xcode doesn't make it obvious how to actually do this.

In my first attempt, I set a breakpoint at the appropriate line of code, and Xcode listed the variables in the Variables View. In my case, that variable was called "response" of type "optional Data". So I first tried typing the following at the debugger prompt:

  ldb> po String(decoding: response.data ?? Data(), as: UTF8.self)

This however will print the string but it will escape all quotes with a backslash. To be able to select and copy unescaped JSON from the console, type the following:

  ldb> e print(String(decoding: response.data ?? Data(), as: UTF8.self))

2022-05-23 Xcode Package.resolved file is corrupted or malformed

Today Xcode gave me the error "Package.resolved file is corrupted or malformed; fix or delete the file to continue: malformed" when opening and running an xcworkspace with a Swift package and a sample app.

That is exactly after a successful pull request, so the project has built successfully before. The problem was fixed by manually removing the file, doing a "clean build folder", then quit Xcode and the simulator. Then started Xcode again and opened the workspace: it built. Just a tip for when you encounter this behavior.

In our case, Xcode actually downgraded some dependant package in (minor) version. So this may not actually be the final solution for you.

Note that this is NOT the same as the error that Xcode 13.2.1 or lower shows when someone else opened it with 13.3 or higher. From that 13.3 version and upwards, Xcode will upgrade the Package.resolved file to a new v2 format. But we never opened the project in any Xcode version higher than 13.2.1. That error reads: "Package.resolved file is corrupted or malformed; fix or delete the file to continue: unsupported schema version 2".

I'm not yet happy with the way Xcode handles Swift Packages, it feels unreliable in the current version. But it'll probably improve in the coming versions.

2022-03-03 Xcode Dependencies could not be resolved

Today, Xcode gave me the following error:

    Dependencies could not be resolved because root depends on 'customerkit' 13.0.0..<14.0.0 and root depends on 'customerkit' 11.0.0..<12.0.0.

The project had built correctly, then I wanted to edit code in a package so I added it as a local package.

The error was confusing to me, because it specifies that root (which means the current project, I assume) depends on both version 11.x and 13.x which is obviously not the case. So what this error message actually means, is: you added a local package, and both the main project and your local package rely on the same package (customerkit in this case), but they require different versions.

The fact that the error twice mentions "root depends on xxx", is thus wrong. If you get it, select your project in the left navigation, select the project again in the middle pane, select the Package Dependencies and look up the version of the dependency. In my case, that was CustomerKit, version "11.0.1 - Next Major". Now for the other packages, check their own dependencies and make sure these are equal.