[英]How to present an alert after view controller has been dismissed
我有一个应用程序,用户在后台上传文件通常需要几秒钟。 当他们点击“完成”按钮时,上传开始,这也将关闭视图控制器。 我希望发生的是下载完成时出现警报。 我以为我只是将下面的代码添加到上载功能中,但它不起作用。 如何显示一个警报框,以确认上传成功?
@IBAction func tapDone(_ sender: Any) {
self.dismiss(animated: true, completion: nil)
if let image = newImage {
submit2Parse(image: image)
}
}
func submit2Parse (image: UIImage) {
if let pfImage = image2PFFile(image: image) {
// Insert PFFile into parse server
let submittedImage = PFObject(className: "Images")
submittedImage["imageFile"] = pfImage
submittedImage["type"] = "submittedFromUserHome"
submittedImage["bride"] = brideSwitch.isOn
submittedImage["groom"] = groomSwitch.isOn
submittedImage["user"] = userSwitch.isOn
submittedImage["picturePeriod"] = pickerSelected
submittedImage["uploadedByUserId"] = PFUser.current()?.objectId ?? "" submittedImage["uploadedByUserName"] = PFUser.current()?.username ?? ""
if !txtIsPlaceHolder { submittedImage["description"] = imageDescription.text }
submittedImage.saveInBackground { (success, error) in
if success {
let message = "Save in bg worked"
print(message)
let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "Ok", style: UIAlertAction.Style.default, handler: {
(action) in
self.dismiss(animated: true, completion: nil)
}))
self.present(alert,animated: true, completion: nil)
} else {
print(error?.localizedDescription ?? "")
}
}
}
}
代码给了我这个构建错误:
封闭中隐式使用“自我”; 使用“自我”。 使捕获语义明确
在tapDone
方法中,您需要利用控制器tapDone
的completion
,如下所示:
self.dismiss(animated: true) {
if let image = newImage {
self.submit2Parse(image: image)
}
}
这仅意味着self.submit2Parse(image: image)
仅在关闭控制器后执行。 此外,错误
封闭中隐式使用“自我”; 使用“自我”。 使捕获语义明确
仅表示您需要使用self.
在闭包内部时显式调用变量或方法。 因此,您的submit2Parse...
现在将如下所示:
self.submit2Parse(image: image)
。
如果我理解正确你的问题,你要解雇你SecondViewController
当用户水龙头tapDone
按钮。 之后,一旦您的图片上传完成,您就希望对成功进行提醒。
但是,如果您在单击按钮后将其dismiss
则您将不会收到任何警报,因为您的SecondViewController
不再处于window hierarchy
并且如果尝试显示警报,则会在Console中收到错误消息,例如:
尝试呈现不在窗口层次结构中的视图!
要解决此问题,您需要从您的第一个视图控制器发出警报,该警报将在您关闭第二个视图控制器后出现,并且可以使用delegate
实现它。
考虑以下示例:
首先在FirstViewController
外部声明一个protocol
:
protocol UplaodSuccessDelegate:class {
func uploadSuccess(message: String)
}
然后确认您的代表参加同一个班级:
class ViewController: FirstViewController, UplaodSuccessDelegate {
那么当您显示SecondViewController
时,您需要传递委托:
let vc = self.storyboard?.instantiateViewController(withIdentifier: "SecondViewController") as! SecondViewController
vc.delegate = self. //Pass delegate
self.present(vc, animated: true, completion: nil)
并将委托方法添加到同一类:
func uploadSuccess(message: String) {
let message = "Save in bg worked"
print(message)
let alert = UIAlertController(title: "title", message: message, preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "Ok", style: UIAlertAction.Style.default, handler: {
(action) in
}))
self.present(alert,animated: true, completion: nil)
}
现在在您的SecondViewController
您需要添加
weak var delegate: UplaodSuccessDelegate?
在您的tapDone
方法中,将代码替换为:
self.dismiss(animated: true) {
if let image = newImage {
submit2Parse(image: image)
}
}
上传完成后,您需要调用委托方法(一旦上传完成),如下所示:
self.delegate?.uploadSuccess(message: "your message")
这将从FirstViewController
调用您的委托方法。
当您将下面的函数放到viewController中以在后台启动数据上传,然后在提交完成时触发的闭包中调用此函数时,即使认为初始视图控制器已被关闭(或已取消,也可以成功创建警报)如果上传时间较长,则将其撤消)。
// This is the function that performs my background upload
func submit2Parse (image: UIImage) {
if let pfImage = image2PFFile(image: image) {
// Insert PFFile into parse server
let submittedImage = PFObject(className: "Images")
submittedImage["imageFile"] = pfImage
submittedImage["imageCreateDt"] = newImageCreateDate
submittedImage["type"] = "submittedFromUserHome"
submittedImage["bride"] = brideSwitch.isOn
submittedImage["groom"] = groomSwitch.isOn
submittedImage["user"] = userSwitch.isOn
submittedImage["picturePeriod"] = pickerSelected
submittedImage["uploadedByUserId"] = PFUser.current()?.objectId ?? ""
submittedImage["uploadedByUserName"] = PFUser.current()?.username ?? ""
if !txtIsPlaceHolder { submittedImage["description"] = imageDescription.text }
// Get the image timestamp, every photo has one
// How do you get the thumbnail image too?
submittedImage.saveInBackground { (success, error) in
if success {
let message = "Save in bg worked"
print(message)
self.showAlertFromAppDelegates()
} else {
print(error?.localizedDescription ?? "")
}
}
}
}
// This is the function that creates the alert
func showAlertFromAppDelegates(){
var topWindow: UIWindow? = UIWindow(frame: UIScreen.main.bounds)
topWindow?.rootViewController = UIViewController()
topWindow?.windowLevel = UIWindow.Level.alert + 1
let alert: UIAlertController = UIAlertController(title: "Upload Complete", message: "Your image was successfully submitted!", preferredStyle: .alert)
alert.addAction(UIAlertAction.init(title: "OK", style: .default, handler: { (alertAction) in
topWindow?.isHidden = true
topWindow = nil
}))
topWindow?.makeKeyAndVisible()
topWindow?.rootViewController?.present(alert, animated: true, completion:nil)
}
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