Kingfisher/Sources/Documentation.docc/Topics/Topic_ImageDataProvider.md

Loading a local image or loading from data

Overview

Kingfisher can set images from a local data source, enabling the processing and management of local image data using Kingfisher's features, without requiring network downloads.

Image from Local File

LocalFileImageDataProvider is a type conforming to ImageDataProvider. It is used to load an image from a local file URL:

let url = URL(fileURLWithPath: path)
let provider = LocalFileImageDataProvider(fileURL: url)
imageView.kf.setImage(with: provider)

You can also pass options to it:

let processor = RoundCornerImageProcessor(cornerRadius: 20)
imageView.kf.setImage(with: provider, options: [.processor(processor)])

Image from Base64 String

Use Base64ImageDataProvider to provide an image from base64 encoded data. All other features you expected, such as cache or image processors, should work as they are as when getting images from an URL.

let provider = Base64ImageDataProvider(base64String: "\/9j\/4AAQSkZJRgABAQA...", cacheKey: "some-cache-key")
imageView.kf.setImage(with: provider)

Generating Image from AVAsset

Use AVAssetImageDataProvider to generate an image from a video URL or AVAsset at a given time:

let provider = AVAssetImageDataProvider(
    assetURL: URL(string: "https://example.com/your_video.mp4")!,
    seconds: 15.0
)

Creating Your Own Image Data Provider

If you want to create your own image data provider type, conform to ImageDataProvider protocol by implementing a cacheKey and a data(handler:) method to provide image data:

struct UserNameLetterIconImageProvider: ImageDataProvider {
    var cacheKey: String { return letter }
    let letter: String
    
    init(userNameFirstLetter: String) {
        self.letter = userNameFirstLetter
    }
    
    func data(handler: @escaping (Result<Data, Error>) -> Void) {
        
        // You can ignore these detail below.
        // It generates some data for an image with `letter` being rendered in the center.

        let letter = self.letter as NSString
        let rect = CGRect(x: 0, y: 0, width: 250, height: 250)
        let renderer = UIGraphicsImageRenderer(size: rect.size)
        let data = renderer.pngData { context in
            UIColor.black.setFill()
            context.fill(rect)
            
            let attributes = [
                NSAttributedString.Key.foregroundColor: UIColor.white,
                                      .font: UIFont.systemFont(ofSize: 200)
            ]
            
            let textSize = letter.size(withAttributes: attributes)
            let textRect = CGRect(
                x: (rect.width - textSize.width) / 2,
                y: (rect.height - textSize.height) / 2,
                width: textSize.width,
                height: textSize.height)
            letter.draw(in: textRect, withAttributes: attributes)
        }

        // Provide the image data in `handler`.
        handler(.success(data))
    }
}

// Set image for user "John"
let provider = UserNameLetterIconImageProvider(userNameFirstLetter: "J")
imageView.kf.setImage(with: provider)

Maybe you have already noticed, the data(handler:) contains a callback to you. You can provide the image data in an asynchronous way from another thread if it is too heavy in the main thread.