iOS/Objective-C: Call AlertViewController from sharedInstance - ios

Question

I am updating some UIAlertViews, deprecated since iOS 9.0 to UIAlertViewControllers.
With UIAlertView, it was possible to just throw an alert from any code being executed--even in a utility class or shared instance--with the simple line:
[alertView show];
So if I call a shared instance such as
- (void)didTapDeleteButton:(id)sender {
NSArray *itemsToDelete = [self.selectedIndexPathToContact allValues];
[[IDModel sharedInstance] deleteItems:itemsToDelete];
//which contains the code:
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Keep Archive Copy?"
message:nil
delegate:self
cancelButtonTitle:#"No"
otherButtonTitles:#"OK",nil];
alertInvite.alertViewStyle = UIAlertViewStyleDefault;
alertInvite.tag=100;
[alertView show];
everything worked fine.
However, with the UIAlertController, this is not allowed. If you put the following code in the method of a class accessible via shared instance, when you get to presentViewController, it throws an error:
UIAlertController *alertView = [UIAlertController alertControllerWithTitle:#"Delete Item?" message:nil preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction* yesButton = [UIAlertAction actionWithTitle:#"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {
[alertView dismissViewControllerAnimated:YES completion:nil];
}];
UIAlertAction* noButton = [UIAlertAction actionWithTitle:#"Not Now" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {
[alertView dismissViewControllerAnimated:YES completion:nil];
}];
[alertView addAction:noButton];
[alertView addAction:yesButton];
if ([alertView respondsToSelector:#selector(setPreferredAction:)]) {
[alertView setPreferredAction:yesButton];
}
//FOLLOWING THROWS ERROR
[self presentViewController:alertView animated:YES completion:nil];
on the last line, that the class (reached via a shared instance) does not have this method. It seems you must use a more complicated way to throw alert. I've seen some somwehat convoluted approaches such as the following:
id rootViewController = [UIApplication sharedApplication].delegate.window.rootViewController;
if([rootViewController isKindOfClass:[UINavigationController class]])
{
rootViewController = ((UINavigationController *)rootViewController).viewControllers.firstObject;
}
if([rootViewController isKindOfClass:[UITabBarController class]])
{
rootViewController = ((UITabBarController *)rootViewController).selectedViewController;
}
[rootViewController presentViewController:alertInvite animated:YES completion:nil];
However, this does not work for me as I don't think my shared instance has a rootviewcontroller. Can anyone suggest a simple, straightforward way to do this?

Answer 1

I created an extension on UIViewController that allows me to create a new window and present a view controller from there. This allows me to present from any class, not just a view controller. Also, it prevents issues where you try to display an alert view from a view controller that is already presenting a view controller.
extension UIViewController {
func presentFromNewWindow(animated: Bool = true, completion: (() -> Void)? = nil) {
let window = newWindow()
if let rootViewController = window.rootViewController {
window.makeKeyAndVisible()
rootViewController.present(self, animated: animated, completion: completion)
}
}
private func newWindow() -> UIWindow {
let window = UIWindow(frame: UIScreen.main.bounds)
let rootViewController = UIViewController()
rootViewController.view.backgroundColor = .clear
window.backgroundColor = .clear
window.rootViewController = rootViewController
window.windowLevel = UIWindowLevelAlert
return window
}
}
You can then use this method to present your Alert Controller (or any UIViewController):
alertViewController.presentFromNewWindow()
When you dismiss the alert view controller, it is removed from the view controller and the window is removed from the hierarchy.

Answer 2

to show an alert from any code I could think of doing:
UIAlertController *alert = [UIAlertController alertControllerWithTitle:#"Alert" message:#"message" preferredStyle:UIAlertControllerStyleAlert];
[alert addAction: [UIAlertAction actionWithTitle:#"Yes" style:UIAlertActionStyleDefault handler:nil]];
alert.TitleColor = [UIColor whiteColor];
id<UIApplicationDelegate> delegate = [UIApplication sharedApplication].delegate;
UIViewController *vc = delegate.window.rootViewController;
[vc presentViewController:alert animated:YES completion:nil];
Note:
Note that in most cases I would NOT do this.
Non ui code shouldn't do ui! Which is likely also part of the reason why apple made the change: It encourages a proper model||view separation

Answer 3

Your question is quite vague, I believe. But I think what you've been looking for is an example of presenting a UIAlertController. Is that correct? If so, continue reading...
Example:
UIAlertController *alert = [UIAlertController alertControllerWithTitle:#"Alert" message:#"message" preferredStyle:UIAlertControllerStyleAlert];
[alert addAction: [UIAlertAction actionWithTitle:#"Yes" style:UIAlertActionStyleDefault handler:nil]];
alert.TitleColor = [UIColor whiteColor];
[self presentViewController:alert animated:YES completion:nil];
doc: https://developer.apple.com/documentation/uikit/uialertcontroller