Programmatically create iOS 13 dynamic images

programmatic-dynamic-images.m

- (UIImage *)dynamicImage
{
    UITraitCollection *const baseTraitCollection = /* an existing trait collection */;
    UITraitCollection *const lightTraitCollection = [UITraitCollection traitCollectionWithTraitsFromCollections:@[baseTraitCollection, [UITraitCollection traitCollectionWithUserInterfaceStyle:UIUserInterfaceStyleLight]]];
    UITraitCollection *const purelyDarkTraitCollection = [UITraitCollection traitCollectionWithUserInterfaceStyle:UIUserInterfaceStyleDark];
    UITraitCollection *const darkTraitCollection = [UITraitCollection traitCollectionWithTraitsFromCollections:@[baseTraitCollection, purelyDarkTraitCollection]];
    
    __block UIImage *lightImage;
    [lightTraitCollection performAsCurrentTraitCollection:^{
        lightImage = /* draw image */;
    }];
    __block UIImage *darkImage;
    [darkTraitCollection performAsCurrentTraitCollection:^{
        darkImage = /* draw image */;
    }];
    [lightImage.imageAsset registerImage:darkImage withTraitCollection:purelyDarkTraitCollection];
    
    return lightImage;
}

This is what worked for me on XCode 13.2 / iOS 15 📦

    static func dynamicImage(light: @autoclosure () -> UIImage, dark: @autoclosure () -> UIImage) -> UIImage {

        let imageAsset = UIImageAsset()
        let lightTraitCollection = UITraitCollection(traitsFrom: [.init(userInterfaceStyle: .light)])
        let darkTraitCollection = UITraitCollection(traitsFrom: [.init(userInterfaceStyle: .dark)])
        imageAsset.register(dark(), with: darkTraitCollection)
        imageAsset.register(light(), with: lightTraitCollection)
        return imageAsset.image(with: .current)
    }

After creating an imageAsset and registering the image with traitCollection more than 65535 times, the image taken by imageAsset.image(with:) will always be wrong.
P.S. Tried all of the above solutions.

After creating an imageAsset and registering the image with traitCollection more than 65535 times, the image taken by imageAsset.image(with:) will always be wrong. P.S. Tried all of the above solutions.

@cragod did you find any solution?

After creating an imageAsset and registering the image with traitCollection more than 65535 times, the image taken by imageAsset.image(with:) will always be wrong. P.S. Tried all of the above solutions.

@cragod did you find any solution?

not yet, just use the cache to delay its occurrence.

After creating an imageAsset and registering the image with traitCollection more than 65535 times, the image taken by imageAsset.image(with:) will always be wrong. P.S. Tried all of the above solutions.

@cragod did you find any solution?

not yet, just use the cache to delay its occurrence.

The reason has been identified:

1. When creating UIImageAsset and registering images, Apple will use an auto-increment as the identifier for the image asset and cache it in a global container. And it will also bind the identifier to the imageAsset object. You can inspect the auto-increment identifier using po [[UIImage new] valueForKeyPath:@"imageAsset._unsafe_mutableCatalog._themeStore._maxNameIdentifier"] in the debugger.
2. However, when retrieving from the cache, Apple will the identifier = {original identifier} & 0xffff. So, the identifier 65536 becomes 1, which causes the unexpected result.