Segue和使用instantiateViewController有什么区别？

Question

Segue和使用instantiateViewController有什么区别？

4

segue和instantiateViewController有什么区别?

我一直在尝试使用segue将图像从一个视图控制器发送到另一个视图控制器，两个答案(Passing Image to another View Controller (Swift) 和 How do I segue an image to another ViewController and display it within an ImageView?)都说要使用segue，但是当尝试使用segue时，我遇到了一些问题，比如照片库关闭后第二个视图控制器没有显示出来，或者图像没有显示出来。

Segue示例

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.destination is XferImageViewController {
        print("Test: ", pickedImage.image)
        let xferVC = segue.destination as? XferImageViewController
        xferVC?.storedImage = pickedImage.image
    }
    print("WHAT IS GOING ON")
//        if segue.destination is XferImageViewController {
//            let xferVC = segue.destination as? XferImageViewController
//            print(pickedImage.image)
//            //xferVC?.storedImage = pickedImage.image
//            xferVC?.storedImage = pickedImageVar
//        }

}

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    if let image = info[UIImagePickerControllerOriginalImage] as? UIImage {
        pickedImage.image = image
    } else {
        print("Something went wrong")
    }
    let image = info[UIImagePickerControllerOriginalImage] as? UIImage
    dismiss(animated:true, completion: nil)
    performSegue(withIdentifier: "xferImage", sender: self)
}

实例化视图控制器示例

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    if let image = info[UIImagePickerControllerOriginalImage] as? UIImage {
        pickedImage.image = image
    } else {
        print("Something went wrong")
    }
    let image = info[UIImagePickerControllerOriginalImage] as? UIImage
    dismiss(animated:true, completion: nil)
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let controller = storyboard.instantiateViewController(withIdentifier: "xferImage") as! XferImageViewController
    controller.storedImage = image
    present(controller, animated: true, completion: nil)
}

使用InstantiateViewController而不是segue后，我得到了想要的结果。两者之间有什么区别？（我确保了segue标识符、尝试了segue.destination和storyboard ID，但仍然无法得到我需要的结果）可能是因为我不知道如何在照片库dismiss调用后使用segue，但我仍然想知道它们的区别。

- LampPost

你在使用segue时有没有在控制台上收到任何消息？如果有，请将该消息添加到问题中。 - Fahri Azimov

2个回答

0

尝试使用以下函数

override func prepare(for segue: UIStoryboardSegue, sender: Any?)
{
    if segue.identifier == "segue"
    {
        if let xferVC = segue.destination as? XferImageViewController {
            xferVC.storedImage = pickedImage.image

                //Why Optional here ?
                //xferVC?.storedImage = pickedImage.image
            }
        }  
  }

- iOS Geek

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Rob · Accepted Answer

问题在于当您初始化segue时，segue对视图控制器层次结构的状态非常特别。您必须将performSegue(withIdentifier:sender:)推迟到dismiss完成后，即将其放入dismiss的完成处理程序中。

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    if let image = info[UIImagePickerControllerOriginalImage] as? UIImage {
        pickedImage.image = image
    } else {
        print("Something went wrong")
    }

    dismiss(animated: true) {
        self.performSegue(withIdentifier: "xferImage", sender: self)
    }
}

上述内容对我很有效。顺便说一句，您可以简化您的prepare(for:sender:)实现：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let xferVC = segue.destination as? XferImageViewController {
        xferVC.storedImage = pickedImage.image
    }
}

两个有些不相关的观察：

If pickedImage is an image view, I'd suggest renaming it (and updating the outlets in your storyboard) to pickedImageView. It's a good convention to avoid confusion between UIImage properties and UIImageView outlets.

This is an even more minor observation, but in Model-View-Controller design, you generally don't want to rely on UIKit objects, like UIImageView to hold model objects, namely the selected image. It suggests a conceptual confusion between "view" objects and "model" objects. Plus, what if the current view controller didn't have a UIImageView?

I'd personally suggest storing the selected image in a separate UIImage? property:

private var selectedImage: UIImage?

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
    if let image = info[UIImagePickerControllerOriginalImage] as? UIImage {
        selectedImage = image

        // if you also want to update a `UIImageView` in the current
        // view controller, fine, do that, but it shouldn't be confused
        // with the "model".
        //
        // pickedImageView.image = image
    } else {
        print("Something went wrong")
    }

    dismiss(animated: true) {
        self.performSegue(withIdentifier: "xferImage", sender: self)
    }
}

And:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let xferVC = segue.destination as? XferImageViewController {
        xferVC.storedImage = selectedImage
    }
}