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private func scale(image ciImage: CIImage?, for scale: CGFloat) -> UIImage {
    guard let ciImage = ciImage else {
        return UIImage()
    }

    let image = UIImage(ciImage: ciImage)
    let size = CGSize(width: image.size.width * scale, height: image.size.height * scale)

    let renderer = UIGraphicsImageRenderer(size: size)

    return renderer.image(actions: { (context) in
        image.draw(in: CGRect(origin: .zero, size: size))
    })
}

I am using this method to scale (and generate before that) images. This is done in background thread and the result is then dispatched back to main thread. However, on image.draw - sometimes 1 out of 10 times, the app crashes with EXC_BAD_ACCESS.

What am I doing wrong? Can I do that in background?

THANKS

rmaddy
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virusss8
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    You shouldn't do UI work in background thread, it should always be done inside the `.main` thread. – Kamran Jun 18 '19 at 12:39

1 Answers1

1

Don't do any UI actions in a background thread. All UI changes must be done in the main thread

Use a dispatch Queue to work in main thread.Try it like this

DispatchQueue.main.async { 
   image.draw(in: CGRect(origin: .zero, size: size))
}

Check this answer to know why we use main thread to perform UI actions

Amal T S
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    If the `draw` method is for `UIImage`, that's not a view method and should work off the main thread, right? See https://stackoverflow.com/questions/10645307/thread-safety-of-uiimage https://developer.apple.com/forums/thread/29031 https://ahmedk92.github.io/2019/03/23/Rendering-off-main-thread-in-iOS.html – Chris Prince Jan 10 '21 at 20:40