Platform-Specific Resources in Catalyst Apps.

Jan 18, 2024

How do I specify platform-specific alternatives for my resources?

In an Asset Catalog, you can simply fiddle with the checkboxes in the Devices section of the Attributes Inspector.

But what about resources that cannot be in an Asset Catalog?

In a traditional multiplatform app, with a target for each supported platform, you can use the Target Membership section of the File Inspector to choose which resources are built into which target.

But what if I’m working on a single-target Catalyst app?

In your target’s setting, the Build Phases section will have a Copy Bundle Resources phase. Its table has a Filters column you can use to specify that a resource is to be copied only on a specific platform.

But what if the resource, for reasons outside of my control, needs to end up in the exact same place on both platforms?

My specific use case had to do with Web Extensions. They require a manifest.json file, which hardcodes paths for things like icons and content scripts, with no option to specify platform-specific alternatives.

Well I couldn’t figure it out, but DTS Engineer Ed Ford came up with a clever trick, and I felt like sharing.

The Trick

Let’s assume you want your target to contain a resource named exactly stuff.data in a directory named exactly resources, but you have two separate versions of this file – one for iOS and one for macOS Catalyst.

Before adding anything to your Xcode project, create this directory structure:

all_resources/
├─ iOS/
│  ├─ resources/
│      ├─ stuff.data <- iOS version
├─ macOS
   ├─ resources/
       ├─ stuff.data <- macOS version

Now in Xcode, using File, Add Files to "ProjectName", add each of the resources directories to your project. Make sure to uncheck all targets from the Add to targets: section. The directories will show up in the project tree as identically named siblings.

Next, in the target’s settings, navigate to Build Phases and look under Copy Bundle Resources. Using the + button, add both resources directories to the phase. It will not be possible to distinguish them before adding them, but don’t worry: you can’t add the same directory twice, and you will be able to tell them apart once added.

Finally, for each directory in this list, change the value in the Filters column using the little filter button. Leave only the appropriate platform checked.

The end result

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