Xcode13中SignUpViewController无法赋值给图片选择器代理的错误

问题核心原因 #

你的代码存在控制器类名不匹配的问题：

• presentPicker()方法属于SignUpViewController，但你给SignInViewController添加了UIImagePickerControllerDelegate和UINavigationControllerDelegate的协议扩展。
• 当前的self（SignUpViewController实例）并未遵守所需协议，因此无法赋值给picker.delegate。

修复步骤 #

将协议扩展的类名从SignInViewController改为SignUpViewController，确保协议实现与当前控制器对应：

@objc func presentPicker(){
    let picker = UIImagePickerController()
    picker.sourceType = .photoLibrary
    picker.allowsEditing = true
    picker.delegate = self // 错误将被修复
    self.present(picker, animated: true, completion: nil)
}


// 修改扩展的所属类为SignUpViewController
extension SignUpViewController: UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        if let imageSelected = info[UIImagePickerController.InfoKey.editedImage] as? UIImage {
            avatar.image = imageSelected
        }

        if let imageOriginal = info[UIImagePickerController.InfoKey.originalImage] as? UIImage {
            avatar.image = imageOriginal
        }
        
        picker.dismiss(animated: true, completion: nil)
    }
}

可选优化 #

你也可以在SignUpViewController的类定义中显式声明协议（Swift中扩展实现协议后类自动遵守，此步骤可选）：

class SignUpViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    // 类内容
}

内容的提问来源于stack exchange，提问作者Anna B.