feat(core): first class a11y support (#8909)

packages/core/accessibility/accessibility-common.ts

@@ -0,0 +1,73 @@
+import type { View } from '../ui/core/view';
+import type { Page } from '../ui/page';
+import type { AccessibilityBlurEventData, AccessibilityFocusChangedEventData, AccessibilityFocusEventData } from './accessibility-types';
+
+const lastFocusedViewOnPageKeyName = '__lastFocusedViewOnPage';
+
+export const accessibilityBlurEvent = 'accessibilityBlur';
+export const accessibilityFocusEvent = 'accessibilityFocus';
+export const accessibilityFocusChangedEvent = 'accessibilityFocusChanged';
+
+/**
+ * Send notification when accessibility focus state changes.
+ * If either receivedFocus or lostFocus is true, 'accessibilityFocusChanged' is send with value true if element received focus
+ * If receivedFocus, 'accessibilityFocus' is send
+ * if lostFocus, 'accessibilityBlur' is send
+ *
+ * @param {View} view
+ * @param {boolean} receivedFocus
+ * @param {boolean} lostFocus
+ */
+export function notifyAccessibilityFocusState(view: View, receivedFocus: boolean, lostFocus: boolean): void {
+	if (!receivedFocus && !lostFocus) {
+		return;
+	}
+
+	view.notify({
+		eventName: accessibilityFocusChangedEvent,
+		object: view,
+		value: !!receivedFocus,
+	} as AccessibilityFocusChangedEventData);
+
+	if (receivedFocus) {
+		if (view.page) {
+			view.page[lastFocusedViewOnPageKeyName] = new WeakRef(view);
+		}
+
+		view.notify({
+			eventName: accessibilityFocusEvent,
+			object: view,
+		} as AccessibilityFocusEventData);
+	} else if (lostFocus) {
+		view.notify({
+			eventName: accessibilityBlurEvent,
+			object: view,
+		} as AccessibilityBlurEventData);
+	}
+}
+
+export function getLastFocusedViewOnPage(page: Page): View | null {
+	try {
+		const lastFocusedViewRef = page[lastFocusedViewOnPageKeyName] as WeakRef<View>;
+		if (!lastFocusedViewRef) {
+			return null;
+		}
+
+		const lastFocusedView = lastFocusedViewRef.get();
+		if (!lastFocusedView) {
+			return null;
+		}
+
+		if (!lastFocusedView.parent || lastFocusedView.page !== page) {
+			return null;
+		}
+
+		return lastFocusedView;
+	} catch {
+		// ignore
+	} finally {
+		delete page[lastFocusedViewOnPageKeyName];
+	}
+
+	return null;
+}