从UIImagePickerController选取的UIImage的cgImage始终为nil的问题求助

核心问题原因 #

从UIImagePickerController获取的图片如果是HEIC格式（iOS相册默认存储格式），UIImage内部实际存储的是CIImage而非CGImage，直接访问cgImage属性自然会返回nil。另外你的代码还有两个隐藏问题：

• 函数名拼写错误：makePuzze应该是makePuzzle，会导致分割逻辑无法被正确调用
• 裁剪坐标系不匹配：UIImage的size是考虑了图片方向的，而CGImage的坐标系以左下角为原点，直接用UIImage.size计算的矩形裁剪会出现位置偏移

修复方案 #

方案1：统一将UIImage转换为CGImage

不管图片是基于CIImage还是CGImage，先转成可用的CGImage实例再进行裁剪，同时修复坐标系和错误处理：

class ViewController: UIViewController, UINavigationControllerDelegate, UIImagePickerControllerDelegate {
    @IBOutlet weak var selectButton: UIButton!
    let picker = UIImagePickerController()

    var image: UIImage!
    var images: [UIImage]!

    override func viewDidLoad() {
        super.viewDidLoad()
        picker.delegate = self
        picker.sourceType = .photoLibrary
    }

    @objc func selectPressed(_ sender: UIButton) {
        present(picker, animated: true)
    }

    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        guard let image = info[.originalImage] as? UIImage else {
            picker.dismiss(animated: true)
            return
        }
        self.image = image
        // 延迟到弹窗消失后执行分割逻辑
        picker.dismiss(animated: true) { [weak self] in
            self?.makePuzzle()
        }
    }

    // 修正拼写错误
    func makePuzzle() {
        guard let splitImages = image.split(times: 5) else {
            print("图片分割失败")
            return
        }
        self.images = splitImages
        // 这里可以添加分割后图片的处理逻辑
    }
}

extension UIImage {
    func split(times: Int) -> [UIImage]? {
        // 优先取cgImage，取不到则将CIImage转成CGImage
        guard let targetCGImage = self.cgImage ?? self.convertToCGImage() else {
            return nil
        }
        
        // 使用CGImage的原始尺寸计算分割块大小（不受UIImage方向影响）
        let totalWidth = targetCGImage.width
        let totalHeight = targetCGImage.height
        let pieceWidth = totalWidth / times
        let pieceHeight = totalHeight / times
        
        var splitImages: [UIImage] = []
        
        // 按CGImage坐标系（左下角为原点）遍历分割
        for y in 0..<times {
            for x in 0..<times {
                let cropRect = CGRect(x: x * pieceWidth, 
                                      y: y * pieceHeight, 
                                      width: pieceWidth, 
                                      height: pieceHeight)
                guard let croppedCGImage = targetCGImage.cropping(to: cropRect) else {
                    continue
                }
                // 保留原图片的缩放比例和方向
                let croppedImage = UIImage(cgImage: croppedCGImage, scale: self.scale, orientation: self.imageOrientation)
                splitImages.append(croppedImage)
            }
        }
        return splitImages
    }
    
    // 辅助方法：将CIImage类型的UIImage转换为CGImage
    private func convertToCGImage() -> CGImage? {
        guard let ciImage = self.ciImage else {
            return nil
        }
        let context = CIContext(options: [.useSoftwareRenderer: false])
        return context.createCGImage(ciImage, from: ciImage.extent)
    }
}

方案2：直接使用CIImage裁剪（适合HEIC图片）

如果图片本身是CIImage类型，可以直接用Core Image API裁剪，避免格式转换的开销：

extension UIImage {
    func splitWithCIImage(times: Int) -> [UIImage]? {
        guard let targetCIImage = self.ciImage ?? CIImage(image: self) else {
            return nil
        }
        let imageExtent = targetCIImage.extent
        let pieceWidth = imageExtent.width / CGFloat(times)
        let pieceHeight = imageExtent.height / CGFloat(times)
        
        var splitImages: [UIImage] = []
        let context = CIContext(options: [.useSoftwareRenderer: false])
        
        for y in 0..<times {
            for x in 0..<times {
                let cropRect = CGRect(x: imageExtent.origin.x + CGFloat(x)*pieceWidth,
                                      y: imageExtent.origin.y + CGFloat(y)*pieceHeight,
                                      width: pieceWidth,
                                      height: pieceHeight)
                let croppedCIImage = targetCIImage.cropped(to: cropRect)
                guard let croppedCGImage = context.createCGImage(croppedCIImage, from: croppedCIImage.extent) else {
                    continue
                }
                let croppedImage = UIImage(cgImage: croppedCGImage, scale: self.scale, orientation: self.imageOrientation)
                splitImages.append(croppedImage)
            }
        }
        return splitImages
    }
}

关键修复点说明 #

1. 兼容CIImage转CGImage：新增convertToCGImage方法，确保所有格式的图片都能拿到可用的CGImage实例
2. 修正坐标系偏差：使用CGImage的原始尺寸计算裁剪区域，避免UIImage方向带来的位置偏移
3. 移除强制解包：用guard let替代!，避免因nil导致的崩溃，同时增加错误提示
4. 修正函数名拼写：将makePuzze改为makePuzzle，确保分割逻辑能被正确调用
5. 优化执行时机：在弹窗消失的回调里执行分割逻辑，避免界面卡顿

内容的提问来源于stack exchange，提问作者Neglected Sanity