iOS 13+ allows users to dismiss FormSheet modals via swipe gesture. When developers prevent dismissal (e.g., for form validation), iOS calls presentationControllerDidAttemptToDismiss but this wasn't exposed in MAUI. Developers had no way to respond when users attempt to dismiss a prevented modal.

Changes

Event Infrastructure

• Added ModalDismissAttemptedEventArgs following existing modal event patterns
• Exposed ModalDismissAttempted event on both Window and Application
• Wired event propagation through NotifyOfWindowModalEvent

iOS Platform

• Implemented DidAttemptToDismiss delegate method in ControlsModalWrapper
• Properly exported and preserved for iOS runtime

Public API

• Updated PublicAPI.Unshipped.txt for all platforms

Usage

// At Window or Application level
Window.ModalDismissAttempted += (s, e) => 
{
    DisplayAlert("Warning", "Save changes before closing", "OK");
};

// Present modal with dismissal prevention
modalPage.On<iOS>().SetModalPresentationStyle(UIModalPresentationStyle.FormSheet);
await Navigation.PushModalAsync(modalPage);

#if IOS
// Prevent interactive dismissal to trigger the event
var presented = handler.PlatformView.PresentingViewController?.PresentedViewController;
if (presented != null)
    presented.ModalInPresentation = true;
#endif

Event fires when user attempts to dismiss a FormSheet modal that has isModalInPresentation = true set on the native view controller.

Custom agent used: uitest-coding-agent
Specialized agent for writing new UI tests for .NET MAUI with proper syntax, style, and conventions

• Fixes [iOS] Modal Formsheet on iOS is currently not cancellable on Shell #6995

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