视图控制器关闭后如何显示警报

Question

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”按钮时开始上传，这也会关闭视图控制器。我希望发生的是在下载完成时出现警报。我以为我只需将下面的代码添加到上传功能，但它不起作用。如何让提示框出现以确认上传成功？

@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：

在闭包中隐式使用“self”；使用“自我”。使捕获语义明确

Answer 1

在您的tapDone 方法中，您需要利用completion 解除您的控制器，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) 只会在您关闭控制器后执行。此外，错误

在闭包中隐式使用“self”；使用“自我”。捕捉 语义显式

仅表示您需要在闭包内使用self. 显式调用变量或方法。所以你的submit2Parse... 现在应该是这样的：

self.submit2Parse(image: image).

Answer 2

如果我正确理解了您的问题，您希望在用户点击 tapDone 按钮时关闭您的 SecondViewController。之后，一旦您的图片上传完成，您就会想要显示成功警报。

但是，如果您dismiss，一旦点击按钮，您将不会收到任何警报，因为您的 SecondViewController 不再在 window hierarchy 中，如果您尝试显示警报，您将在控制台中收到错误消息，例如：

尝试在 谁的观点不在 窗口层次结构！

要解决此问题，您需要在您的第一个视图控制器中显示一个警报，该警报将在您关闭第二个视图控制器后出现，您可以通过 delegate 实现它。

考虑下面的例子：

首先在你的FirstViewController之外声明一个protocol：

protocol UplaodSuccessDelegate:class {
    func uploadSuccess(message: String)
}

然后确认你的代表到同一个班级：

class ViewController: FirstViewController, UplaodSuccessDelegate {

那么你在提交SecondViewController时需要传递委托：

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个类：

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)
}

现在你需要在SecondViewController 中添加

weak var delegate: UplaodSuccessDelegate?

并在您的 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（上传完成后），例如：

self.delegate?.uploadSuccess(message: "your message")

这将从FirstViewController 调用您的委托方法。

Answer 3

当您将下面的函数放入在后台启动数据上传的 viewController 中，然后在提交完成时触发的闭包中调用此函数时，即使初始视图控制器是被解雇（如果上传时间很长，则被解雇）。

// 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)
    }