引用以下两篇文章，已经很详细说明路由原理了
https://juejin.im/post/5c8db8e8f265da2d864b889f
https://juejin.im/post/5c8db8fff265da2de52dd80f
opaque和maintainState
- opaque：是否是全屏不透明的，当一个组件opaque=true时，那么可以认为它之下的组件都不需要再绘制了。一般情况下，一个 Page 的opaque=true， 不是全屏的 PopupWindow opaque=false。
- maintainState：一个已经不可见(被上面的盖住完全看不到啦~)的组件，是否还需要保存状态。当maintainState=true时，会让这个组件继续活着，但不会再进行绘制操作了。如果maintainState=false，则不会继续维持这个 Widget 的生存状态了。
# class OverlayState
@override
Widget build(BuildContext context) {
// This list is filled backwards and then reversed below before
// it is added to the tree.
final List<Widget> children = <Widget>[];
bool onstage = true;
int onstageCount = 0;
for (int i = _entries.length - 1; i >= 0; i -= 1) {
final OverlayEntry entry = _entries[i];
if (onstage) {
onstageCount += 1;
children.add(_OverlayEntryWidget(
key: entry._key,
entry: entry,
));
if (entry.opaque)
onstage = false;
} else if (entry.maintainState) {
children.add(_OverlayEntryWidget(
key: entry._key,
entry: entry,
tickerEnabled: false,
));
}
}
///_Theatre父类是MultiChildRenderObjectWidget
return _Theatre(
skipCount: children.length - onstageCount,
children: children.reversed.toList(growable: false),
);
}
Overlay rebuild的时候是会调用
List<OverlayEntry> _entries内OverlayEntry的builder方法rebuild child widget的
OverlayState
- OverlayState中页面存储在_entries中
final List<OverlayEntry> _entries = <OverlayEntry>[]; - 通过insert和_remove方法可以增删OverlayEntry
void insert(OverlayEntry entry, { OverlayEntry below, OverlayEntry above }) {
...
///OverlayEntry持有OverlayState
entry._overlay = this;
...
}
void _remove(OverlayEntry entry)
- OverlayEntry可以自己将自身从OverlayState中删除
void remove() {
...
overlay._remove(this);
...
}
NavigatorState
- NavigatorState使用了Overlay管理页面
- 传递给Overlay的OverlayEntry由各Route自己管理
///NavigatorState class
Iterable<OverlayEntry> get _allRouteOverlayEntries sync* {
for (final _RouteEntry entry in _history)
yield* entry.route.overlayEntries;
}
@override
Widget build(BuildContext context) {
...
Overlay(
key: _overlayKey,
initialEntries: overlay == null ? _allRouteOverlayEntries.toList(growable: false) : const <OverlayEntry>[],
),
...
}
- NavigatorState中存的是_RouteEntry
List<_RouteEntry> _history = <_RouteEntry>[];
_RouteEntry(
///Route
this.route, {
@required _RouteLifecycle initialState,
})
- _RouteEntry有个currentState值标识_RouteEntry当前状态，当为add和push状态时，调用entry的方法最终会调用Route的install方法，从而创建Route的OverlayEntry
void _flushHistoryUpdates({bool rearrangeOverlay = true}) {
...
int index = _history.length - 1;
...
final List<_RouteEntry> toBeDisposed = <_RouteEntry>[];
while (index >= 0) {
switch (entry.currentState) {
case _RouteLifecycle.add:
assert(rearrangeOverlay);
entry.handleAdd(
navigator: this,
previousPresent: _getRouteBefore(index - 1, _RouteEntry.isPresentPredicate)?.route,
);
assert(entry.currentState == _RouteLifecycle.adding);
continue;
case _RouteLifecycle.adding:
if (canRemoveOrAdd || next == null) {
entry.didAdd(
navigator: this,
isNewFirst: next == null
);
assert(entry.currentState == _RouteLifecycle.idle);
continue;
}
break;
case _RouteLifecycle.push:
case _RouteLifecycle.pushReplace:
case _RouteLifecycle.replace:
assert(rearrangeOverlay);
entry.handlePush(
navigator: this,
previous: previous?.route,
previousPresent: _getRouteBefore(index - 1, _RouteEntry.isPresentPredicate)?.route,
isNewFirst: next == null,
);
...
break;
...
}
}
/// A route that displays widgets in the [Navigator]'s [Overlay].
abstract class OverlayRoute<T> extends Route<T> {
/// Creates a route that knows how to interact with an [Overlay].
OverlayRoute({
RouteSettings settings,
}) : super(settings: settings);
/// Subclasses should override this getter to return the builders for the overlay.
@factory
Iterable<OverlayEntry> createOverlayEntries();
@override
List<OverlayEntry> get overlayEntries => _overlayEntries;
final List<OverlayEntry> _overlayEntries = <OverlayEntry>[];
@override
void install() {
assert(_overlayEntries.isEmpty);
_overlayEntries.addAll(createOverlayEntries());
super.install();
}
- ModalRoute会创建两个OverlayEntry，_modalBarrier为遮罩，_modalScope为page本身
abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T> {
...
@override
Iterable<OverlayEntry> createOverlayEntries() sync* {
yield _modalBarrier = OverlayEntry(builder: _buildModalBarrier);
yield _modalScope = OverlayEntry(builder: _buildModalScope, maintainState: maintainState);
}
...
}
Route有一个_popCompleter属性
final Completer<T> _popCompleter = Completer<T>();
当NavigatorState push一个Route的时候返回的就是_popCompleter.future,当pop的时候也是通过_popCompleter.complete(result ?? currentResult);传递返回值
MaterialApp
MaterialApp(
routes: {'main': (context) => Counter()},
onGenerateRoute: (setting) {
// setting.name
return MaterialPageRoute(builder: (_) => Counter());
},
),
_MaterialAppState内使用了WidgetsApp，pushName的时候先判断routes是否有，routes没有再返回widget.onGenerateRoute(settings)
WidgetsApp(
routes: widget.routes,
onGenerateRoute: widget.onGenerateRoute,
)
Route<dynamic> _onGenerateRoute(RouteSettings settings) {
final String name = settings.name;
final WidgetBuilder pageContentBuilder = name == Navigator.defaultRouteName && widget.home != null
? (BuildContext context) => widget.home
: widget.routes[name];
if (pageContentBuilder != null) {
final Route<dynamic> route = widget.pageRouteBuilder<dynamic>(
settings,
pageContentBuilder,
);
return route;
}
if (widget.onGenerateRoute != null)
return widget.onGenerateRoute(settings);
return null;
}
Widget build(BuildContext context) {
Widget navigator;
if (_navigator != null) {
navigator = Navigator(
...
onGenerateRoute: _onGenerateRoute,
...
);
}
}
路由管理封装
https://github.com/LBXjixiangniao/flutter_summary/blob/master/lib/router/router.dart
