Swift - best way to show alert with loading indicator right away after button is clicked?

Question

I tried using the main thread to show but it didn't work, any thought why the alert doesn't show up right away?

@IBAction func updateData(_ sender: Any) {
    let alert = UIAlertController(title: "Updating data", message: "Please wait...", preferredStyle: .alert)
    alert.view.tintColor = UIColor.black
    let loadingIndicator: UIActivityIndicatorView = UIActivityIndicatorView(frame: CGRect(x: 10,y: 5,width: 50, height: 50)) as UIActivityIndicatorView
    loadingIndicator.hidesWhenStopped = true
    loadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.gray
    loadingIndicator.startAnimating();

    alert.view.addSubview(loadingIndicator)
    DispatchQueue.main.async {
        self.present(alert, animated: true)

    }

Answer 1

UIAlertController can not be customized, so for me the best solution was to create a custom UIView XIB and then instatiate it on the ViewController I need.

The XIB View could be like this:

then you create a CustomAlertLoadingView.swift file which subclass UIView, associate it to the XIB and create the IBOutlets.

To show it in any ViewController just create this extension

extension UIViewController {
     func presentAlert(title: String) {
        let nib = UINib(nibName: "CustomAlertLoadingView", bundle: nil)
        let customAlert = nib.instantiate(withOwner: self, options: nil).first as! CustomAlertLoadingView

        customAlert.tag = 12345
        customAlert.titleAlertLabel.text = title
        customAlert.indicator.startAnimating()


        let screen = UIScreen.main.bounds
        customAlert.center = CGPoint(x: screen.midX, y: screen.midY)

        self.view.addSubview(customAlert)
    }
}

use self.yourViewController.presentAlert(title:"yourTitle")

To dismiss the alert, create this function inside the UIVIewController extension

func dismissCustomAlert() {
        if let view = self.view.viewWithTag(12345) {
            view.removeFromSuperview()
        }
}

then call self.yourViewController.dismissCustomAlert

Answer 2

I ran this through Xcode without any delay:

@IBAction func updateData(_ sender: UIButton) {
    print("button fire")
    let alert = UIAlertController(title: "Updating data", message: "Please wait...", preferredStyle: .alert)
    alert.view.tintColor = UIColor.black
    let loadingIndicator: UIActivityIndicatorView = UIActivityIndicatorView(frame: CGRect(x: 10,y: 5,width: 50, height: 50)) as UIActivityIndicatorView
    loadingIndicator.hidesWhenStopped = true
    loadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.gray
    loadingIndicator.startAnimating();

    alert.view.addSubview(loadingIndicator)
    self.present(alert, animated: true)

}

I replaced the sender parameter of your function with a UIButton and took out the Dispatch call to the main queue since it's unnecessary. No delays at all!

When you say that there is a delay do you mean only when you step trough the code? Because yes if you're stepping through it, the alert view won't be displayed right after self.present(alert, animated: true). You'll have to wait until the function completes execution. But that "delay" isn't visible to the human eye. Did you trying running the above code without stepping through it?