Accessing Bounds on Multiple UIAlertViews: Solutions and Considerations

Understanding UIAlertViews and Their Bounds

When it comes to displaying multiple UIAlertViews in an iOS app, one common issue developers face is accessing the bounds of these alerts. In this article, we’ll delve into the world of UIKit and explore why the bounds of UIAlertViews are not always what they seem.

What Are UIAlertViews?

UIAlertViews are a part of the UIKit framework in iOS and provide a way to display alert messages to the user. They can be customized with titles, messages, buttons, and even images. These alerts can be used for various purposes, such as displaying errors, asking for user input, or providing information.

Understanding Bounds

In the context of UIAlertViews, bounds refer to the rectangular area where the alert will be displayed on the screen. The bounds contain four values: x-coordinate, y-coordinate, width, and height. These values represent the position and size of the alert box.

Problem Accessing Bounds on Multiple UIAlertViews

The provided code snippet illustrates a common issue developers encounter when trying to access the bounds of multiple UIAlertViews. In this example, two alerts are created, one after another, but only the first alert displays its correct bounds. The subsequent alerts display an origin of 0,0 and incorrect width and height values.

- (void)viewDidLoad {
    [super viewDidLoad];

    [self makeAlert:@"Zero alert" withMessage:@"This is the zero alert"];

    UIAlertView *firstAlert = [[UIAlertView alloc] initWithTitle:@"First Alert" message:@"Here is the first alert" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [firstAlert show];
    NSLog(@"first alert bounds, origin: %f, %f  size: %f, %f",firstAlert.bounds.origin.x,firstAlert.bounds.origin.y,firstAlert.bounds.size.width,firstAlert.bounds.size.height);
    [firstAlert release];

    UIAlertView *secondAlert = [[UIAlertView alloc] initWithTitle:@"Second Alert" message:@"Here is the second alert" delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [secondAlert show];
    NSLog(@"second alert bounds, origin: %f, %f  size: %f, %f",firstAlert.bounds.origin.x,firstAlert.bounds.origin.y,firstAlert.bounds.size.width,firstAlert.bounds.size.height);
    [secondAlert release];

    [self makeAlert:@"Third Alert" withMessage:@"Here is the third alert."];
    [self makeAlert:@"Fourth Alert" withMessage:@"Here is the fourth alert."];
}

- (void)makeAlert:(NSString *)makeTitle withMessage:(NSString *)makeMessage {
    UIAlertView *newAlert = [[UIAlertView alloc] initWithTitle:makeTitle message:makeMessage delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [newAlert show];
    NSLog(@"%@ alert bounds, origin: %f, %f  size: %f, %f",makeTitle,newAlert.bounds.origin.x,newAlert.bounds.origin.y,newAlert.bounds.size.width,newAlert.bounds.size.height);
    [newAlert release];
}

Why Are Bounds Incorrect?

The answer lies in how UIAlertViews are displayed on the screen. According to the official documentation, the frames of UIAlertViews are computed just before showing. This means that the bounds of an alert can change dynamically based on various factors such as the size of the screen, the size of the alert itself, and even the position of other views on the screen.

Solution: Using a UIAlertViewDelegate

One way to get accurate bounds information for UIAlertViews is by implementing a UIAlertViewDelegate. This delegate provides methods that can be used to monitor the state of an alert as it’s being displayed. One such method is - (void)willPresentAlertView:(UIAlertView *)alertView.

- (void)alertViewControllerWillPresentView:(UIAlertView *)alertView {
    NSLog(@"Alert view will present view, bounds: %f, %f  size: %f, %f", alertView.bounds.origin.x, alertView.bounds.origin.y, alertView.bounds.size.width, alertView.bounds.size.height);
}

By implementing this delegate and logging the bounds information in the alertViewControllerWillPresentView method, we can see that the bounds are computed just before presenting the view.

- (void)viewDidLoad {
    [super viewDidLoad];

    [self makeAlert:@"Zero alert" withMessage:@"This is the zero alert"];

    UIAlertView *firstAlert = [[UIAlertView alloc] initWithTitle:@"First Alert" message:@"Here is the first alert" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [firstAlert show];

    NSLog(@"Alert view will present view, bounds: %f, %f  size: %f, %f", firstAlert.bounds.origin.x, firstAlert.bounds.origin.y, firstAlert.bounds.size.width, firstAlert.bounds.size.height);
}

- (void)alertViewControllerWillPresentView:(UIAlertView *)alertView {
    NSLog(@"Alert view will present view, bounds: %f, %f  size: %f, %f", alertView.bounds.origin.x, alertView.bounds.origin.y, alertView.bounds.size.width, alertView.bounds.size.height);
}

Alternative Solution: Rolling Your Own UIAlertView Class

If refactoring your code to work with a UIAlertViewDelegate is not feasible, another option is to roll your own UIAlertView class. There are several open-source implementations available on GitHub, such as the TSAlertView.

By using an existing implementation or creating your own, you can avoid the complexities of working with native UIAlertViews and ensure that your alerts display correctly.

Conclusion

In conclusion, accessing the bounds of multiple UIAlertViews in iOS can be challenging due to the dynamic nature of their display. By implementing a UIAlertViewDelegate, logging the bounds information just before presenting the view, or rolling your own UIAlertView class, you can overcome this issue and ensure that your alerts display correctly on the screen.

Additional Considerations

When working with UIAlertViews, keep in mind that their frames are computed just before showing. This means that the bounds of an alert can change dynamically based on various factors such as the size of the screen, the size of the alert itself, and even the position of other views on the screen.

Additionally, if you’re using a custom implementation of UIAlertView, make sure to consider the implications of overriding its behavior. By default, UIAlertViews provide a way to display alerts with titles, messages, buttons, and images. However, when creating your own implementation, you’ll need to decide how to handle these features and ensure that they display correctly.

By understanding the intricacies of UIAlertViews and their bounds, you can create more robust and user-friendly interfaces in your iOS apps.

Last modified on 2023-12-02