UIImage slow loading in a UIPageViewController - ios

Question

I have a UIPageViewController showing a UIViewController that contains a UIImageView.
The images displayed in the UIImageView originally come from the camera roll. I copy them in the application's folder. When I display the UIPageViewController, it loads the image for the current page and displays it:
if let image = UIImage(contentsOfFile: imagePath) {
imageView.image = image
}
The problem is that it's really slow. Loading the first image is slow and then swiping is very slow.
I am testing this on my iPhone 5. I installed the app through XCode. Is there a way to make it faster? Should I save a smaller version of the image when I save the images from the camera roll into my application's folder?

Answer 1

You could preload the images like Sergii suggested or load the images a background thread to avoid blocking the main thread.
NSOperationQueue().addOperationWithBlock {
if let image = UIImage(contentsOfFile: imagePath) {
NSOperationQueue.mainQueue().addOperationWithBlock {
self.imageView.image = image
}
}
}

Answer 2

You can load images you'll need before transitioning to UIPageViewController. Also, take a look at some projects for image caches
FastImageCache, SDWebImage, Haneke
Also, you can be interest in this article Avoiding Image Decompression Sickness

Answer 3

To increase the speed of swiping you'd need to move where you are assigning the image to the UIImageView from the main thread to a background thread.
There are a few ways to do this...
Using NSOperationQueue
NSOperationQueue().addOperationWithBlock {
if let image = UIImage(contentsOfFile: imagePath) {
NSOperationQueue.mainQueue().addOperationWithBlock {
self.imageView.image = image
}
}
}
Or you can use GCD and calling dispatch_async()
if let image = UIImage(contentsOfFile: imagePath) {
dispatch_async(dispatch_get_main_queue()) {
imageView.image = image
}
}
With regards to saving an image from the Camera Roll when/if you save it to your apps file system you could try using:
let qualityFloat = 1.0
let imageData = UIImageJPEGRepresentation(imageFromCameraRoll, qualityFloat)
Playing around with qualityFloat (between 0.0 - 1.0) will change the file size of the image which could help you with the loading times.