100 Days of Swift

3. For a tougher challenge, take the image generation code out of cellForRowAt: generate all images when the app first launches, and use those smaller versions instead. For bonus points, combine the getDocumentsDirectory() method I introduced in project 10 so that you save the resulting cache to make sure it never happens again.

As a reminder, here’s the code for getDocumentsDirectory():

func getDocumentsDirectory() -> URL {

    let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)

    return paths[0]
}

The above is from Day 98 of Paul Hudson's excellent course: 100 Days of Swift. It is Challenge #3 and there is even a "bonus" challenge inside the challenge! In approaching the solution--before coding--I wrote down my thoughts and then gathered snippets of code that I thought would help. My notes are below. I thought it might be helpful for others to share them without giving away the solution.

First, I jotted down the four main things I was concerned with:

1. Read big images from bundle, see project 1.
2. Render a image into a rect using CoreGraphics like in project 30. 
3. Read the thumbnails in like project 10. 
4. If a thumbnail does not exist then create it. Also like in project 10.

Next, I gathered the corresponding snippets of the code:

From project 1:

DispatchQueue.global(qos: .userInitiated).async { [weak self] in

    let fm = FileManager.default

    let path = Bundle.main.resourcePath!

    let items = try! fm.contentsOfDirectory(atPath: path)

    

    let pictureNames = items

        .filter { $0.hasPrefix("nssl") }

        .sorted { $0 < $1 }

    

    self?.storms = pictureNames.map {

        Storm(name: $0, imageName: $0) }

    

    DispatchQueue.main.async { [weak self] in

        self?.collectionView.reloadData()

    }

}

From project 30:

        let path = Bundle.main.path(forResource: imageRootName, ofType: nil)!

        let original = UIImage(contentsOfFile: path)!

        let renderRect = CGRect(origin: .zero, size: CGSize(width: 90, height: 90))

        let renderer = UIGraphicsImageRenderer(size: renderRect.size)

        

        let rounded = renderer.image { ctx in

            ctx.cgContext.addEllipse(in: renderRect)

            ctx.cgContext.clip()

            

            original.draw(in: renderRect)

        }

From project 10:

Write:

        let imageName = UUID().uuidString

        let imagePath = getDocumentsDirectory().appendingPathComponent(imageName)

        if let jpegData = image.jpegData(compressionQuality: 0.8) {

            try? jpegData.write(to: imagePath)

        }

Read:

        let path = getDocumentsDirectory().appendingPathComponent(person.imageName)

        cell.imageView.image = UIImage(contentsOfFile: path.path)