Swift 如何实现懒加载

通过懒加载来实现从相册或拍照添加图片
1、声明懒加载属性imagePickerController

lazy var imagePickerController: UIImagePickerController = {
    let vc = UIImagePickerController.init()
    vc.delegate = self
    vc.allowsEditing = true
    return vc
}()

2、显示相册和拍照选项的SheetView

func showSheetView() -> Void {
    let alertController = UIAlertController(title: nil, message: nil, preferredStyle: .actionSheet)
    // 拍照选项
    let takingPicturesAction = UIAlertAction(title:"拍照", style: .default)
    {
        action in
        if UIImagePickerController.isSourceTypeAvailable(.camera) {
            self.imagePickerController.sourceType = .camera;
            self.present(self.imagePickerController, animated: true, completion: nil)
        } else {
            print("当前设备不支持拍照")
        }
    }
    // 相册选项
    let photoLibraryAction = UIAlertAction(title:"相册", style: .default)
    {
        action in
        self.imagePickerController.sourceType = .photoLibrary;
        self.present(self.imagePickerController, animated: true, completion: nil)
    }
    // 取消选项
    let cancelAction = UIAlertAction(title:"取消", style: .cancel, handler: nil)
    alertController.addAction(takingPicturesAction)
    alertController.addAction(photoLibraryAction)
    alertController.addAction(cancelAction)
    self.present(alertController, animated:true, completion:nil)
}

3、获取imagePickerController返回的图片

// MARK: - UIImagePickerControllerDelegate, UINavigationControllerDelegate
extension AddProductController : UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        // 获取照片
        let image : UIImage = info[UIImagePickerController.InfoKey.editedImage] as! UIImage
        addPictureButton.setImage(image, for: .normal)
        addPictureButton.setTitle("", for: .normal)
        self.dismiss(animated: true, completion: nil)
    }
}