cocoa - 如何在 Swift 4 中压缩 NSImage

Question

我正在为 Mac OS 开发应用程序，我无法找到任何压缩 NSImage 并将其转换为 Swift 4 的 base64 编码字符串的方法。

我几乎找不到Swift3代码

 func compressUnderMegaBytes(megabytes: CGFloat) -> NSImage? {
        var compressionRatio = 1.0
        var imageRep = NSBitmapImageRep(data: self.tiffRepresentation!)
        var options = NSDictionary(object: NSNumber(floatLiteral: compressionRatio), forKey: NSBitmapImageRep.PropertyKey.compressionFactor as NSCopying)
        var compressedData: Data? = imageRep?.representation(using: .jpeg, properties: options as! [NSBitmapImageRep.PropertyKey : Any])
        while compressedData?.length > (megabytes * 1024 * 1024) {
            compressionRatio = compressionRatio * 0.9
            options = NSDictionary(object: NSNumber(floatLiteral:compressionRatio), forKey: NSBitmapImageRep.PropertyKey.compressionFactor as NSCopying)
            compressedData = imageRep?.representation(using:.png, properties: options as! [NSBitmapImageRep.PropertyKey : Any])
            if compressionRatio <= 0.4 {
                break
            }
        }
        return NSImage(data: compressedData!)
    }

但转换为 Swift 4 后出现以下错误

Answer 1

翻译后的代码相当繁琐。 NSDictionary detour 在 Swift 4 中不是必需的。

length 已重命名为 count

extension NSImage {
    func compressUnderMegaBytes(megabytes: CGFloat) -> NSImage? {

        var compressionRatio = 1.0
        guard let tiff = self.tiffRepresentation, let imageRep = NSBitmapImageRep(data: tiff) else { return nil }
        var compressedData = imageRep.representation(using: .jpeg, properties: [.compressionFactor : compressionRatio])!
        while CGFloat(compressedData.count) > megabytes * 1024 * 1024 {
            compressionRatio = compressionRatio * 0.9
            compressedData = imageRep.representation(using: .png, properties:  [.compressionFactor : compressionRatio])!
            if compressionRatio <= 0.4 {
                break
            }
        }
        return NSImage(data: compressedData)
    }
}

或者没有不安全的未包装选项

extension NSImage {
    func compressUnderMegaBytes(megabytes: CGFloat) -> NSImage? {

        var compressionRatio = 1.0
        guard let tiff = self.tiffRepresentation, let imageRep = NSBitmapImageRep(data: tiff) else { return nil }
        var compressedData = imageRep.representation(using: .jpeg, properties: [.compressionFactor : compressionRatio])
        if compressedData == nil { return self }
        while CGFloat(compressedData!.count) > megabytes * 1024 * 1024 {
            compressionRatio = compressionRatio * 0.9
            let newCompressedData = imageRep.representation(using: .png, properties:  [.compressionFactor : compressionRatio])
            if compressionRatio <= 0.4 || newCompressedData == nil {
                break
            }
            compressedData = newCompressedData
        }
        return NSImage(data: compressedData!)
    }
}

注意:是否打算第一次压缩为jpg，然后压缩为png？