fix lifecycle in nested page view.

Author: chenenyu

lib/src/dispatch_lifecycle_to_parent_page_mixin.dart renamed to lib/src/child_page_dispatch_lifecycle_mixin.dart

@@ -4,7 +4,7 @@ import 'child_page_lifecycle_wrapper.dart';
 import 'lifecycle_aware.dart';
 
 /// Lifecycle dispatcher for child page.
-mixin DispatchLifecycleToParentPageMixin
+mixin ChildPageDispatchLifecycleMixin
     on State<ChildPageLifecycleWrapper>, LifecycleAware {
   Set<LifecycleAware> _subscribers = <LifecycleAware>{};
 

lib/src/child_page_lifecycle_wrapper.dart

@@ -1,9 +1,9 @@
 import 'package:flutter/material.dart';
 
-import 'dispatch_lifecycle_to_parent_page_mixin.dart';
+import 'child_page_dispatch_lifecycle_mixin.dart';
+import 'child_page_subscribe_lifecycle_mixin.dart';
 import 'lifecycle_aware.dart';
 import 'parent_page_lifecycle_wrapper.dart';
-import 'subscribe_lifecycle_from_parent_page_mixin.dart';
 
 /// Lifecycle wrapper for children of [PageView] and [TabBarView].
 /// See [ParentPageLifecycleWrapper].
@@ -37,8 +37,8 @@ class ChildPageLifecycleWrapper extends StatefulWidget {
 class ChildPageLifecycleWrapperState extends State<ChildPageLifecycleWrapper>
     with
         LifecycleAware,
-        DispatchLifecycleToParentPageMixin,
-        SubscribeLifecycleFromParentPageMixin,
+        ChildPageDispatchLifecycleMixin,
+        ChildPageSubscribeLifecycleMixin,
         AutomaticKeepAliveClientMixin {
   @override
   bool get wantKeepAlive => widget.wantKeepAlive ?? false;

lib/src/subscribe_lifecycle_from_parent_page_mixin.dart renamed to lib/src/child_page_subscribe_lifecycle_mixin.dart

@@ -6,7 +6,7 @@ import 'parent_page_lifecycle_wrapper.dart';
 
 /// Subscribe lifecycle event from [ParentPageLifecycleWrapper].
 /// This is used in child page of PageView.
-mixin SubscribeLifecycleFromParentPageMixin
+mixin ChildPageSubscribeLifecycleMixin
     on State<ChildPageLifecycleWrapper>, LifecycleAware {
   ParentPageLifecycleWrapperState _basePageViewLifecycleWrapperState;
 

lib/src/dispatch_lifecycle_to_child_page_mixin.dart renamed to lib/src/parent_page_dispatch_lifecycle_mixin.dart

@@ -4,7 +4,7 @@ import 'lifecycle_aware.dart';
 import 'parent_page_lifecycle_wrapper.dart';
 
 /// Dispatch lifecycle event to child page.
-mixin DispatchLifecycleToChildPageMixin
+mixin ParentPageDispatchLifecycleMixin
     on State<ParentPageLifecycleWrapper>, LifecycleAware {
   /// Current page.
   int curPage;
@@ -24,6 +24,8 @@ mixin DispatchLifecycleToChildPageMixin
 
   /// Dispatch event to stream subscription
   void dispatchEvent(LifecycleEvent event) {
-    _subscribers[curPage].onLifecycleEvent(event);
+    if (_subscribers[curPage] != null) {
+      _subscribers[curPage].onLifecycleEvent(event);
+    }
   }
 }

lib/src/parent_page_lifecycle_wrapper.dart

@@ -2,10 +2,9 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 
-import 'dispatch_lifecycle_to_child_page_mixin.dart';
 import 'lifecycle_aware.dart';
-import 'lifecycle_mixin.dart';
-import 'subscribe_lifecycle_from_child_page_mixin.dart';
+import 'parent_page_dispatch_lifecycle_mixin.dart';
+import 'parent_page_subscribe_lifecycle_mixin.dart';
 
 /// Lifecycle wrapper for [PageView]/[TabBarView].
 class ParentPageLifecycleWrapper extends StatefulWidget {
@@ -44,9 +43,8 @@ abstract class ParentPageLifecycleWrapperState
     extends State<ParentPageLifecycleWrapper>
     with
         LifecycleAware,
-        LifecycleMixin,
-        DispatchLifecycleToChildPageMixin,
-        SubscribeLifecycleFromChildPageMixin {
+        ParentPageDispatchLifecycleMixin,
+        ParentPageSubscribeLifecycleMixin {
   void onPageChanged();
 
   @override
@@ -95,8 +93,12 @@ class _PageViewLifecycleWrapperState extends ParentPageLifecycleWrapperState {
     // print('_PageViewLifecycleWrapperState#initState');
     _pageController = widget.controller;
     curPage = _pageController.initialPage;
-    // 补发第一个page的 active 事件
-    Future.microtask(() => dispatchEvent(LifecycleEvent.active));
+    // 补发第一个page的 active 事件, 异步是让 active 事件在 push 事件之后
+    Future.microtask(() {
+      if (widget.onLifecycleEvent != null) {
+        widget.onLifecycleEvent(LifecycleEvent.active);
+      }
+    });
   }
 
   /// 页面切换监听
@@ -119,8 +121,12 @@ class _TabBarViewLifecycleWrapperState extends ParentPageLifecycleWrapperState {
     // print('_TabBarViewLifecycleWrapperState#initState');
     _tabController = widget.controller;
     curPage = _tabController.index;
-    // 补发第一个page的 active 事件
-    Future.microtask(() => dispatchEvent(LifecycleEvent.active));
+    // 补发第一个page的 active 事件, 异步是让 active 事件在 push 事件之后
+    Future.microtask(() {
+      if (widget.onLifecycleEvent != null) {
+        widget.onLifecycleEvent(LifecycleEvent.active);
+      }
+    });
   }
 
   @override

lib/src/parent_page_subscribe_lifecycle_mixin.dart

@@ -0,0 +1,35 @@
+import 'package:flutter/widgets.dart';
+
+import 'child_page_lifecycle_wrapper.dart';
+import 'lifecycle_aware.dart';
+import 'lifecycle_observer.dart';
+import 'lifecycle_observer_provider.dart';
+import 'parent_page_lifecycle_wrapper.dart';
+
+/// Subscribe lifecycle event from [ChildPageLifecycleWrapper] or [LifecycleObserver].
+mixin ParentPageSubscribeLifecycleMixin
+    on State<ParentPageLifecycleWrapper>, LifecycleAware {
+  ChildPageLifecycleWrapperState _pageLifecycleWrapperState;
+  LifecycleObserver _lifecycleObserver;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    _pageLifecycleWrapperState = ChildPageLifecycleWrapper.of(context);
+    if (_pageLifecycleWrapperState != null) {
+      // 如果是嵌套的PageView，则从上层Page订阅event
+      _pageLifecycleWrapperState.subscribe(this);
+    } else {
+      // 如果不是嵌套的PageView，则从LifecycleObserver订阅event
+      _lifecycleObserver = LifecycleObserverProvider.of(context);
+      _lifecycleObserver.subscribe(this, ModalRoute.of(context));
+    }
+  }
+
+  @override
+  void dispose() {
+    _pageLifecycleWrapperState?.unsubscribe(this);
+    _lifecycleObserver?.unsubscribe(this);
+    super.dispose();
+  }
+}