Drawing cache

gistfile1.swift

private let drawingCache = NSCache()

public extension UIImage {
    public class func imageForSize(size: CGSize, opaque: Bool = false, drawingBlock: () -> Void) -> UIImage {
        assert(size != CGSize.zeroSize)
        
        UIGraphicsBeginImageContextWithOptions(size, opaque, 0.0)
        drawingBlock()
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext();
        
        return image
    }
    
    public class func imageForIdentifier(identifier: String, opaque: Bool = false, size: CGSize, drawingBlock: () -> Void) -> UIImage {
        if let image = drawingCache.objectForKey(identifier) as? UIImage {
            assert(image.size == size, "Cached image size doesn't match the requested image size")
            return image
        }
        
        let image = self.imageForSize(size, opaque: opaque, drawingBlock: drawingBlock)
        drawingCache.setObject(image, forKey: identifier)
        return image
    }
    
    public class func imageForIdentifier(identifier: String) -> UIImage? {
        return drawingCache.objectForKey(identifier) as? UIImage
    }
    
    public class func removeImageForIdentifier(identifier: String) {
        drawingCache.removeObjectForKey(identifier)
    }
    
    public class func removeAllCachedImages() {
        drawingCache.removeAllObjects()
    }
}