ios - imageview 未相应更新

Question

我想用从照片库中选择的照片创建一个 ImageView ，并通过按下按钮显示在 ScrollView 中。但是选择后图像不会显示，只有当我再次按下按钮时才会显示。有人可以帮我解决这个问题吗？

@IBAction func imageBtnPressed(_ sender: Any) {

    imagePicker()

    let imageView = UIImageView(frame: CGRect(x: (scrollView.bounds.size.width-200)/2, y:(scrollView.bounds.size.height-100)/2, width: 200, height: 100))
    imageView.image = imageOnCanvas
    imageView.contentMode = .scaleAspectFill
    imageView.clipsToBounds = true
    scrollView.addSubview(imageView)

}


func imagePicker(){
    let imagePicker = UIImagePickerController()
    imagePicker.delegate = self
    imagePicker.sourceType = .photoLibrary
    imagePicker.allowsEditing = false
    present(imagePicker, animated: true, completion: nil)
}


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


func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {

    let selectedImage = info[.originalImage] as? UIImage
    imageOnCanvas = selectedImage
    dismiss(animated: true, completion: nil)
}

Answer 1

您的代码不会因为 UIImagePickerController 出现而暂停。那么，让我们看看您的代码:

@IBAction func imageBtnPressed(_ sender: Any) {
    imagePicker()
    let imageView = UIImageView(frame: CGRect(x: (scrollView.bounds.size.width-200)/2, y:(scrollView.bounds.size.height-100)/2, width: 200, height: 100))
    imageView.image = imageOnCanvas
    imageView.contentMode = .scaleAspectFill
    imageView.clipsToBounds = true
    scrollView.addSubview(imageView)
}
func imagePicker(){
    let imagePicker = UIImagePickerController()
    imagePicker.delegate = self
    imagePicker.sourceType = .photoLibrary
    imagePicker.allowsEditing = false
    present(imagePicker, animated: true, completion: nil)
}

所以这完全就像在说(用 imagePicker 函数的内容代替函数调用):

@IBAction func imageBtnPressed(_ sender: Any) {
    let imagePicker = UIImagePickerController()
    imagePicker.delegate = self
    imagePicker.sourceType = .photoLibrary
    imagePicker.allowsEditing = false
    present(imagePicker, animated: true, completion: nil)
    let imageView = UIImageView(frame: CGRect(x: (scrollView.bounds.size.width-200)/2, y:(scrollView.bounds.size.height-100)/2, width: 200, height: 100))
    imageView.image = imageOnCanvas
    imageView.contentMode = .scaleAspectFill
    imageView.clipsToBounds = true
    scrollView.addSubview(imageView)
}

好吧，你可以清楚地看到，你指的是 imageOnCanvas 还没有被设置。 imagePicker 仍在显示；用户尚未选择照片。但是你的代码已经完全结束了。您继续添加了一个 subview ，该 subview 由 ImageView 组成，该 ImageView 包含 imageOnCanvas 在代码开始之前中的图像。