app lifecycle mixin

app_lifecycle_mixin.dart

// Copyright 2025 Fredrick Allan Grott. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

import 'package:flutter/material.dart';
import 'package:lifecycle/lifecycle.dart';
import 'package:userinterface/core/lifecycle/app_lifecycle_globals.dart';

/// Subscribes lifecycle events for normal widgets.
/// This is used to wrap the scaffold of the app so that
/// we have non-null appView and appDisplay globals.
/// 
/// One still puts the defaultLifecycleObserver from the 
/// Lifecycle package in the navigationObservers slot
/// of the MaterialApp.route constructor.
mixin AppLifecycleMixin<T extends StatefulWidget> on State<T>, LifecycleAware {
  LifecycleObserver? _lifecycleObserver;
  WidgetDispatchLifecycleMixin? _widgetDispatchLifecycleMixin;

  @override
  void initState() {
    super.initState();
    // Dispatches [LifecycleEvent.push] event.
    handleLifecycleEvents([LifecycleEvent.push]);
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    final ModalRoute? route = ModalRoute.of(context);
    // Avoids re-subscribe when a route is popping.
    // When called Navigator#pop(), the [_RouteLifecycle] will change to [popping],
    // then notify the [NavigatorObserver].
    //
    // 如果当前route正在popping，避免重复订阅。
    if (route == null || !route.isActive) return;

    // grab appView
    appView = View.maybeOf(context);

    // 重新查找 [WidgetDispatchLifecycleMixin]。
    _widgetDispatchLifecycleMixin = null;
    context.visitAncestorElements((element) {
      if (element is StatefulElement && element.state is WidgetDispatchLifecycleMixin) {
        _widgetDispatchLifecycleMixin = element.state as WidgetDispatchLifecycleMixin;
        return false;
      }
      return true;
    });
    // 优先从 [WidgetDispatchLifecycleMixin] 中订阅。
    if (_widgetDispatchLifecycleMixin != null) {
      _widgetDispatchLifecycleMixin!.subscribe(this);
    } else {
      _lifecycleObserver = LifecycleObserver.internalGet(context);
      _lifecycleObserver!.subscribe(this, route);
    }
  }

  // To prevent letter-boxing on fodlables, see
  // https://docs.flutter.dev/ui/adaptive-responsive/large-screens
  void didChangeMetrics() {
    // so now we can use appDisplay to get devicePixelRatio and size
    // without using MediaQueryData.fromView( FlutterView view)
    // This will prevent letter-boxing with foldables.
    appDisplay =  appView?.display;
  }

  @override
  void dispose() {
    // Dispatches [LifecycleEvent.pop].
    handleLifecycleEvents([LifecycleEvent.pop]);
    _lifecycleObserver?.unsubscribe(this);
    _widgetDispatchLifecycleMixin?.unsubscribe(this);
    super.dispose();
  }
}