Multi-window (9.1): windows, resolvers, and the launch-event migration

Core 9.1 models every UI surface as a NativeWindow with a role ('application' | 'embedded' | 'carplay' | 'externalDisplay') and state ('attached' | 'detached' | 'closed'). Even a single-window app runs through this model.

Reaching windows

import { Application } from '@nativescript/core';

Application.primaryWindow;          // the main app window
Application.activeWindow;           // the one currently focused (differs on iPad side-by-side)
Application.getWindows('all');      // every live window, filterable by role
Application.getWindowById(id);

Per-window environment replaces the deprecated app-level getters: Application.orientation(), Application.systemAppearance() and Application.layoutDirection() are deprecated in favor of Application.primaryWindow?.orientation() etc. — on multi-window iPad the window's values are the truthful ones (a side-by-side window can be compact while the device is landscape).

Providing content: setWindowContentResolver