Kingfisher/Sources/Documentation.docc/CommonTasks/CommonTasks_Serializer.md

Common Tasks - Serializer

CacheSerializer is utilized to convert data into an image object for retrieval from disk cache, and conversely, for storing images to the disk cache.

Use the default serializer

// Just without anything
imageView.kf.setImage(with: url)
// It equals to
imageView.kf.setImage(with: url, options: [.cacheSerializer(DefaultCacheSerializer.default)])

DefaultCacheSerializer is responsible for converting cached data into a corresponding image object and vice versa. It supports PNG, JPEG, and GIF formats by default.

Enforce a format

To enforce a specific image format, use FormatIndicatedCacheSerializer, which offers serializers for all supported formats: FormatIndicatedCacheSerializer/png, FormatIndicatedCacheSerializer/jpeg, and FormatIndicatedCacheSerializer/gif.

Use PNG serializer when rounding image corner

While DefaultCacheSerializer aims to preserve the original format of input image data, there are scenarios where this behavior might not meet your needs. For example, when using a RoundCornerImageProcessor, it's often desirable to maintain an alpha channel for transparency around the corners. JPEG images, lacking an alpha channel, would not support this transparency when saved. To ensure the presence of an alpha channel by converting images to PNG, you can set the PNG serializer explicitly:

let roundCorner = RoundCornerImageProcessor(cornerRadius: 20)
imageView.kf.setImage(with: url, 
    options: [.processor(roundCorner), 
              .cacheSerializer(FormatIndicatedCacheSerializer.png)]
)

Creating customized serializer

Make a type conforming to CacheSerializer by implementing data(with:original:) and image(with:options:): To create a type that conforms to CacheSerializer, implement the CacheSerializer/data(with:original:) and CacheSerializer/image(with:options:):

struct MyCacheSerializer: CacheSerializer {
    func data(with image: Image, original: Data?) -> Data? {
        return MyFramework.data(of: image)
    }
    
    func image(with data: Data, options: KingfisherParsedOptionsInfo?) -> Image? {
        return MyFramework.createImage(from: data)
    }
}

Then pass it to the KingfisherWrapper/setImage(with:placeholder:options:completionHandler:)-9h820 methods:

let serializer = MyCacheSerializer()
let url = URL(string: "https://yourdomain.com/example.png")
imageView.kf.setImage(with: url, options: [.cacheSerializer(serializer)])