Question

我是Xcode和Swift的新手。我目前正在玩Apple的Start Developing iOS Apps (Swift)教程。

到目前为止一切正常，除了一件事。本教程处理主ViewController类中的Image Picker委托，使其符合UIImagePickerControllerDelegate和UINavigationControllerDelegate协议。我想尝试别的东西并将委托移到单独的类。这就是我的所作所为：

import UIKit
import Foundation

class MealPhotoDelegate: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    var placeholder: UIImageView?

    func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
        dismiss(animated: true, completion: nil)
    }

    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
        guard let selectedImage = info[UIImagePickerControllerOriginalImage] as? UIImage else {
            fatalError("Expected a dictionary containing an image, but was provided the following: \(info)")
        }

        placeholder!.image = selectedImage

        dismiss(animated: true, completion: nil)
    }
}

在ViewController：

@IBAction func selectImageFromPhotoLibrary(_ sender: UITapGestureRecognizer) {
    nameTextField.resignFirstResponder()

    let imagePickerController = UIImagePickerController()
    imagePickerController.sourceType = .photoLibrary

    let imagePickerDelegate = MealPhotoDelegate()
    imagePickerDelegate.placeholder = photoImageView

    imagePickerController.delegate = imagePickerDelegate

    present(imagePickerController, animated: true, completion: nil)
}

每次出现图像选择器时以及浏览照片时，都会生成错误：

2017-07-20 01:49：00.937470 + 0200 FoodTracker [41600：4236501] API错误：（null）返回0宽度，假设UIViewNoIntrinsicMetric

我做错了什么？ UIViewController是否可以选择代表的超类？我觉得可能不是。

Answer 1

您的问题是内存管理问题。在selectImageFromPhotoLibrary内，您可以创建MealPhotoDelegate的本地实例。在方法结束时，此实例超出范围并被取消分配，因为没有强引用。因此，图片选择器的代理人变为nil，但它无法正常工作。

解决方案是强烈引用MealPhotoDelegate的实例。使用视图控制器类中的属性可以轻松完成此操作。

将以下属性添加到视图控制器类：

var imagePickerDelegate: MealPhotoDelegate?

然后更新一行：

let imagePickerDelegate = MealPhotoDelegate()

使用：

imagePickerDelegate = MealPhotoDelegate()

那就是它。它现在可以工作了。

作为旁注，您MealPhotoDelegate没有理由延长UIViewController。改为扩展NSObject。而且您可以使用正确的代码修复新问题。

这是怎么回事：

class MealPhotoDelegate: NSObject, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    var placeholder: UIImageView?

    func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
        picker.dismiss(animated: true, completion: nil)
    }

    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
        guard let selectedImage = info[UIImagePickerControllerOriginalImage] as? UIImage else {
            fatalError("Expected a dictionary containing an image, but was provided the following: \(info)")
        }

        if let placeholder = placeholder {
            placeholder.image = selectedImage
        }

        picker.dismiss(animated: true, completion: nil)
    }
}

图像选择器控制器代表在单独的类中不起作用

1 个答案: