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Programmatically create iOS 13 dynamic images
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- (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; | |
} |
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The reason has been identified:
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 usingpo [[UIImage new] valueForKeyPath:@"imageAsset._unsafe_mutableCatalog._themeStore._maxNameIdentifier"]
in the debugger.identifier = {original identifier} & 0xffff
. So, the identifier65536
becomes1
, which causes the unexpected result.