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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'dart:async';
import 'dart:developer' as developer;
import 'dart:ui' show AppLifecycleState, Locale, AccessibilityFeatures;
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter/services.dart';
import 'app.dart';
import 'debug.dart';
import 'focus_manager.dart';
import 'framework.dart';
import 'widget_inspector.dart';
export 'dart:ui' show AppLifecycleState, Locale;
/// Interface for classes that register with the Widgets layer binding.
///
/// When used as a mixin, provides no-op method implementations.
///
/// See [WidgetsBinding.addObserver] and [WidgetsBinding.removeObserver].
///
/// This class can be extended directly, to get default behaviors for all of the
/// handlers, or can used with the `implements` keyword, in which case all the
/// handlers must be implemented (and the analyzer will list those that have
/// been omitted).
///
/// {@tool sample}
///
/// This [StatefulWidget] implements the parts of the [State] and
/// [WidgetsBindingObserver] protocols necessary to react to application
/// lifecycle messages. See [didChangeAppLifecycleState].
///
/// ```dart
/// class AppLifecycleReactor extends StatefulWidget {
/// const AppLifecycleReactor({ Key key }) : super(key: key);
///
/// @override
/// _AppLifecycleReactorState createState() => _AppLifecycleReactorState();
/// }
///
/// class _AppLifecycleReactorState extends State<AppLifecycleReactor> with WidgetsBindingObserver {
/// @override
/// void initState() {
/// super.initState();
/// WidgetsBinding.instance.addObserver(this);
/// }
///
/// @override
/// void dispose() {
/// WidgetsBinding.instance.removeObserver(this);
/// super.dispose();
/// }
///
/// AppLifecycleState _notification;
///
/// @override
/// void didChangeAppLifecycleState(AppLifecycleState state) {
/// setState(() { _notification = state; });
/// }
///
/// @override
/// Widget build(BuildContext context) {
/// return Text('Last notification: $_notification');
/// }
/// }
/// ```
/// {@end-tool}
///
/// To respond to other notifications, replace the [didChangeAppLifecycleState]
/// method above with other methods from this class.
abstract class WidgetsBindingObserver {
/// Called when the system tells the app to pop the current route.
/// For example, on Android, this is called when the user presses
/// the back button.
///
/// Observers are notified in registration order until one returns
/// true. If none return true, the application quits.
///
/// Observers are expected to return true if they were able to
/// handle the notification, for example by closing an active dialog
/// box, and false otherwise. The [WidgetsApp] widget uses this
/// mechanism to notify the [Navigator] widget that it should pop
/// its current route if possible.
///
/// This method exposes the `popRoute` notification from
/// [SystemChannels.navigation].
Future<bool> didPopRoute() => Future<bool>.value(false);
/// Called when the host tells the app to push a new route onto the
/// navigator.
///
/// Observers are expected to return true if they were able to
/// handle the notification. Observers are notified in registration
/// order until one returns true.
///
/// This method exposes the `pushRoute` notification from
/// [SystemChannels.navigation].
Future<bool> didPushRoute(String route) => Future<bool>.value(false);
/// Called when the application's dimensions change. For example,
/// when a phone is rotated.
///
/// This method exposes notifications from [Window.onMetricsChanged].
///
/// {@tool sample}
///
/// This [StatefulWidget] implements the parts of the [State] and
/// [WidgetsBindingObserver] protocols necessary to react when the device is
/// rotated (or otherwise changes dimensions).
///
/// ```dart
/// class MetricsReactor extends StatefulWidget {
/// const MetricsReactor({ Key key }) : super(key: key);
///
/// @override
/// _MetricsReactorState createState() => _MetricsReactorState();
/// }
///
/// class _MetricsReactorState extends State<MetricsReactor> with WidgetsBindingObserver {
/// @override
/// void initState() {
/// super.initState();
/// WidgetsBinding.instance.addObserver(this);
/// }
///
/// @override
/// void dispose() {
/// WidgetsBinding.instance.removeObserver(this);
/// super.dispose();
/// }
///
/// Size _lastSize;
///
/// @override
/// void didChangeMetrics() {
/// setState(() { _lastSize = WidgetsBinding.instance.window.physicalSize; });
/// }
///
/// @override
/// Widget build(BuildContext context) {
/// return Text('Current size: $_lastSize');
/// }
/// }
/// ```
/// {@end-tool}
///
/// In general, this is unnecessary as the layout system takes care of
/// automatically recomputing the application geometry when the application
/// size changes.
///
/// See also:
///
/// * [MediaQuery.of], which provides a similar service with less
/// boilerplate.
void didChangeMetrics() { }
/// Called when the platform's text scale factor changes.
///
/// This typically happens as the result of the user changing system
/// preferences, and it should affect all of the text sizes in the
/// application.
///
/// This method exposes notifications from [Window.onTextScaleFactorChanged].
///
/// {@tool sample}
///
/// ```dart
/// class TextScaleFactorReactor extends StatefulWidget {
/// const TextScaleFactorReactor({ Key key }) : super(key: key);
///
/// @override
/// _TextScaleFactorReactorState createState() => _TextScaleFactorReactorState();
/// }
///
/// class _TextScaleFactorReactorState extends State<TextScaleFactorReactor> with WidgetsBindingObserver {
/// @override
/// void initState() {
/// super.initState();
/// WidgetsBinding.instance.addObserver(this);
/// }
///
/// @override
/// void dispose() {
/// WidgetsBinding.instance.removeObserver(this);
/// super.dispose();
/// }
///
/// double _lastTextScaleFactor;
///
/// @override
/// void didChangeTextScaleFactor() {
/// setState(() { _lastTextScaleFactor = WidgetsBinding.instance.window.textScaleFactor; });
/// }
///
/// @override
/// Widget build(BuildContext context) {
/// return Text('Current scale factor: $_lastTextScaleFactor');
/// }
/// }
/// ```
/// {@end-tool}
///
/// See also:
///
/// * [MediaQuery.of], which provides a similar service with less
/// boilerplate.
void didChangeTextScaleFactor() { }
/// {@macro on_platform_brightness_change}
void didChangePlatformBrightness() { }
/// Called when the system tells the app that the user's locale has
/// changed. For example, if the user changes the system language
/// settings.
///
/// This method exposes notifications from [Window.onLocaleChanged].
void didChangeLocales(List<Locale> locale) { }
/// Called when the system puts the app in the background or returns
/// the app to the foreground.
///
/// An example of implementing this method is provided in the class-level
/// documentation for the [WidgetsBindingObserver] class.
///
/// This method exposes notifications from [SystemChannels.lifecycle].
void didChangeAppLifecycleState(AppLifecycleState state) { }
/// Called when the system is running low on memory.
///
/// This method exposes the `memoryPressure` notification from
/// [SystemChannels.system].
void didHaveMemoryPressure() { }
/// Called when the system changes the set of currently active accessibility
/// features.
///
/// This method exposes notifications from [Window.onAccessibilityFeaturesChanged].
void didChangeAccessibilityFeatures() { }
}
/// The glue between the widgets layer and the Flutter engine.
mixin WidgetsBinding on BindingBase, SchedulerBinding, GestureBinding, RendererBinding, SemanticsBinding {
@override
void initInstances() {
super.initInstances();
_instance = this;
buildOwner.onBuildScheduled = _handleBuildScheduled;
window.onLocaleChanged = handleLocaleChanged;
window.onAccessibilityFeaturesChanged = handleAccessibilityFeaturesChanged;
SystemChannels.navigation.setMethodCallHandler(_handleNavigationInvocation);
SystemChannels.system.setMessageHandler(_handleSystemMessage);
}
/// The current [WidgetsBinding], if one has been created.
///
/// If you need the binding to be constructed before calling [runApp],
/// you can ensure a Widget binding has been constructed by calling the
/// `WidgetsFlutterBinding.ensureInitialized()` function.
static WidgetsBinding get instance => _instance;
static WidgetsBinding _instance;
@override
void initServiceExtensions() {
super.initServiceExtensions();
if (!kReleaseMode) {
registerSignalServiceExtension(
name: 'debugDumpApp',
callback: () {
debugDumpApp();
return debugPrintDone;
},
);
registerBoolServiceExtension(
name: 'showPerformanceOverlay',
getter: () =>
Future<bool>.value(WidgetsApp.showPerformanceOverlayOverride),
setter: (bool value) {
if (WidgetsApp.showPerformanceOverlayOverride == value)
return Future<void>.value();
WidgetsApp.showPerformanceOverlayOverride = value;
return _forceRebuild();
},
);
registerServiceExtension(
name: 'didSendFirstFrameEvent',
callback: (_) async {
return <String, dynamic>{
// This is defined to return a STRING, not a boolean.
// Devtools, the Intellij plugin, and the flutter tool all depend
// on it returning a string and not a boolean.
'enabled': _needToReportFirstFrame ? 'false' : 'true',
};
},
);
// Expose the ability to send Widget rebuilds as [Timeline] events.
registerBoolServiceExtension(
name: 'profileWidgetBuilds',
getter: () async => debugProfileBuildsEnabled,
setter: (bool value) async {
if (debugProfileBuildsEnabled != value)
debugProfileBuildsEnabled = value;
},
);
}
assert(() {
registerBoolServiceExtension(
name: 'debugAllowBanner',
getter: () => Future<bool>.value(WidgetsApp.debugAllowBannerOverride),
setter: (bool value) {
if (WidgetsApp.debugAllowBannerOverride == value)
return Future<void>.value();
WidgetsApp.debugAllowBannerOverride = value;
return _forceRebuild();
},
);
// This service extension is deprecated and will be removed by 12/1/2018.
// Use ext.flutter.inspector.show instead.
registerBoolServiceExtension(
name: 'debugWidgetInspector',
getter: () async => WidgetsApp.debugShowWidgetInspectorOverride,
setter: (bool value) {
if (WidgetsApp.debugShowWidgetInspectorOverride == value)
return Future<void>.value();
WidgetsApp.debugShowWidgetInspectorOverride = value;
return _forceRebuild();
},
);
WidgetInspectorService.instance.initServiceExtensions(registerServiceExtension);
return true;
}());
}
Future<void> _forceRebuild() {
if (renderViewElement != null) {
buildOwner.reassemble(renderViewElement);
return endOfFrame;
}
return Future<void>.value();
}
/// The [BuildOwner] in charge of executing the build pipeline for the
/// widget tree rooted at this binding.
BuildOwner get buildOwner => _buildOwner;
final BuildOwner _buildOwner = BuildOwner();
/// The object in charge of the focus tree.
///
/// Rarely used directly. Instead, consider using [FocusScope.of] to obtain
/// the [FocusScopeNode] for a given [BuildContext].
///
/// See [FocusManager] for more details.
FocusManager get focusManager => _buildOwner.focusManager;
final List<WidgetsBindingObserver> _observers = <WidgetsBindingObserver>[];
/// Registers the given object as a binding observer. Binding
/// observers are notified when various application events occur,
/// for example when the system locale changes. Generally, one
/// widget in the widget tree registers itself as a binding
/// observer, and converts the system state into inherited widgets.
///
/// For example, the [WidgetsApp] widget registers as a binding
/// observer and passes the screen size to a [MediaQuery] widget
/// each time it is built, which enables other widgets to use the
/// [MediaQuery.of] static method and (implicitly) the
/// [InheritedWidget] mechanism to be notified whenever the screen
/// size changes (e.g. whenever the screen rotates).
///
/// See also:
///
/// * [removeObserver], to release the resources reserved by this method.
/// * [WidgetsBindingObserver], which has an example of using this method.
void addObserver(WidgetsBindingObserver observer) => _observers.add(observer);
/// Unregisters the given observer. This should be used sparingly as
/// it is relatively expensive (O(N) in the number of registered
/// observers).
///
/// See also:
///
/// * [addObserver], for the method that adds observers in the first place.
/// * [WidgetsBindingObserver], which has an example of using this method.
bool removeObserver(WidgetsBindingObserver observer) => _observers.remove(observer);
@override
void handleMetricsChanged() {
super.handleMetricsChanged();
for (WidgetsBindingObserver observer in _observers)
observer.didChangeMetrics();
}
@override
void handleTextScaleFactorChanged() {
super.handleTextScaleFactorChanged();
for (WidgetsBindingObserver observer in _observers)
observer.didChangeTextScaleFactor();
}
@override
void handlePlatformBrightnessChanged() {
super.handlePlatformBrightnessChanged();
for (WidgetsBindingObserver observer in _observers)
observer.didChangePlatformBrightness();
}
@override
void handleAccessibilityFeaturesChanged() {
super.handleAccessibilityFeaturesChanged();
for (WidgetsBindingObserver observer in _observers)
observer.didChangeAccessibilityFeatures();
}
/// Called when the system locale changes.
///
/// Calls [dispatchLocaleChanged] to notify the binding observers.
///
/// See [Window.onLocaleChanged].
@protected
@mustCallSuper
void handleLocaleChanged() {
dispatchLocalesChanged(window.locales);
}
/// Notify all the observers that the locale has changed (using
/// [WidgetsBindingObserver.didChangeLocales]), giving them the
/// `locales` argument.
///
/// This is called by [handleLocaleChanged] when the [Window.onLocaleChanged]
/// notification is received.
@protected
@mustCallSuper
void dispatchLocalesChanged(List<Locale> locales) {
for (WidgetsBindingObserver observer in _observers)
observer.didChangeLocales(locales);
}
/// Notify all the observers that the active set of [AccessibilityFeatures]
/// has changed (using [WidgetsBindingObserver.didChangeAccessibilityFeatures]),
/// giving them the `features` argument.
///
/// This is called by [handleAccessibilityFeaturesChanged] when the
/// [Window.onAccessibilityFeaturesChanged] notification is received.
@protected
@mustCallSuper
void dispatchAccessibilityFeaturesChanged() {
for (WidgetsBindingObserver observer in _observers)
observer.didChangeAccessibilityFeatures();
}
/// Called when the system pops the current route.
///
/// This first notifies the binding observers (using
/// [WidgetsBindingObserver.didPopRoute]), in registration order, until one
/// returns true, meaning that it was able to handle the request (e.g. by
/// closing a dialog box). If none return true, then the application is shut
/// down by calling [SystemNavigator.pop].
///
/// [WidgetsApp] uses this in conjunction with a [Navigator] to
/// cause the back button to close dialog boxes, return from modal
/// pages, and so forth.
///
/// This method exposes the `popRoute` notification from
/// [SystemChannels.navigation].
@protected
Future<void> handlePopRoute() async {
for (WidgetsBindingObserver observer in List<WidgetsBindingObserver>.from(_observers)) {
if (await observer.didPopRoute())
return;
}
SystemNavigator.pop();
}
/// Called when the host tells the app to push a new route onto the
/// navigator.
///
/// This notifies the binding observers (using
/// [WidgetsBindingObserver.didPushRoute]), in registration order, until one
/// returns true, meaning that it was able to handle the request (e.g. by
/// opening a dialog box). If none return true, then nothing happens.
///
/// This method exposes the `pushRoute` notification from
/// [SystemChannels.navigation].
@protected
@mustCallSuper
Future<void> handlePushRoute(String route) async {
for (WidgetsBindingObserver observer in List<WidgetsBindingObserver>.from(_observers)) {
if (await observer.didPushRoute(route))
return;
}
}
Future<dynamic> _handleNavigationInvocation(MethodCall methodCall) {
switch (methodCall.method) {
case 'popRoute':
return handlePopRoute();
case 'pushRoute':
return handlePushRoute(methodCall.arguments);
}
return Future<dynamic>.value();
}
@override
void handleAppLifecycleStateChanged(AppLifecycleState state) {
super.handleAppLifecycleStateChanged(state);
for (WidgetsBindingObserver observer in _observers)
observer.didChangeAppLifecycleState(state);
}
/// Called when the operating system notifies the application of a memory
/// pressure situation.
///
/// Notifies all the observers using
/// [WidgetsBindingObserver.didHaveMemoryPressure].
///
/// This method exposes the `memoryPressure` notification from
/// [SystemChannels.system].
void handleMemoryPressure() {
for (WidgetsBindingObserver observer in _observers)
observer.didHaveMemoryPressure();
}
Future<void> _handleSystemMessage(Object systemMessage) async {
final Map<String, dynamic> message = systemMessage;
final String type = message['type'];
switch (type) {
case 'memoryPressure':
handleMemoryPressure();
break;
}
return;
}
bool _needToReportFirstFrame = true;
int _deferFirstFrameReportCount = 0;
bool get _reportFirstFrame => _deferFirstFrameReportCount == 0;
/// Whether the first frame has finished rendering.
///
/// Only useful in profile and debug builds; in release builds, this always
/// return false. This can be deferred using [deferFirstFrameReport] and
/// [allowFirstFrameReport]. The value is set at the end of the call to
/// [drawFrame].
///
/// This value can also be obtained over the VM service protocol as
/// `ext.flutter.didSendFirstFrameEvent`.
bool get debugDidSendFirstFrameEvent => !_needToReportFirstFrame;
/// Tell the framework not to report the frame it is building as a "useful"
/// first frame until there is a corresponding call to [allowFirstFrameReport].
///
/// This is used by [WidgetsApp] to avoid reporting frames that aren't useful
/// during startup as the "first frame".
void deferFirstFrameReport() {
if (!kReleaseMode) {
assert(_deferFirstFrameReportCount >= 0);
_deferFirstFrameReportCount += 1;
}
}
/// When called after [deferFirstFrameReport]: tell the framework to report
/// the frame it is building as a "useful" first frame.
///
/// This method may only be called once for each corresponding call
/// to [deferFirstFrameReport].
///
/// This is used by [WidgetsApp] to report when the first useful frame is
/// painted.
void allowFirstFrameReport() {
if (!kReleaseMode) {
assert(_deferFirstFrameReportCount >= 1);
_deferFirstFrameReportCount -= 1;
}
}
void _handleBuildScheduled() {
// If we're in the process of building dirty elements, then changes
// should not trigger a new frame.
assert(() {
if (debugBuildingDirtyElements) {
throw FlutterError(
'Build scheduled during frame.\n'
'While the widget tree was being built, laid out, and painted, '
'a new frame was scheduled to rebuild the widget tree. '
'This might be because setState() was called from a layout or '
'paint callback. '
'If a change is needed to the widget tree, it should be applied '
'as the tree is being built. Scheduling a change for the subsequent '
'frame instead results in an interface that lags behind by one frame. '
'If this was done to make your build dependent on a size measured at '
'layout time, consider using a LayoutBuilder, CustomSingleChildLayout, '
'or CustomMultiChildLayout. If, on the other hand, the one frame delay '
'is the desired effect, for example because this is an '
'animation, consider scheduling the frame in a post-frame callback '
'using SchedulerBinding.addPostFrameCallback or '
'using an AnimationController to trigger the animation.'
);
}
return true;
}());
ensureVisualUpdate();
}
/// Whether we are currently in a frame. This is used to verify
/// that frames are not scheduled redundantly.
///
/// This is public so that test frameworks can change it.
///
/// This flag is not used in release builds.
@protected
bool debugBuildingDirtyElements = false;
/// Pump the build and rendering pipeline to generate a frame.
///
/// This method is called by [handleDrawFrame], which itself is called
/// automatically by the engine when when it is time to lay out and paint a
/// frame.
///
/// Each frame consists of the following phases:
///
/// 1. The animation phase: The [handleBeginFrame] method, which is registered
/// with [Window.onBeginFrame], invokes all the transient frame callbacks
/// registered with [scheduleFrameCallback], in
/// registration order. This includes all the [Ticker] instances that are
/// driving [AnimationController] objects, which means all of the active
/// [Animation] objects tick at this point.
///
/// 2. Microtasks: After [handleBeginFrame] returns, any microtasks that got
/// scheduled by transient frame callbacks get to run. This typically includes
/// callbacks for futures from [Ticker]s and [AnimationController]s that
/// completed this frame.
///
/// After [handleBeginFrame], [handleDrawFrame], which is registered with
/// [Window.onDrawFrame], is called, which invokes all the persistent frame
/// callbacks, of which the most notable is this method, [drawFrame], which
/// proceeds as follows:
///
/// 3. The build phase: All the dirty [Element]s in the widget tree are
/// rebuilt (see [State.build]). See [State.setState] for further details on
/// marking a widget dirty for building. See [BuildOwner] for more information
/// on this step.
///
/// 4. The layout phase: All the dirty [RenderObject]s in the system are laid
/// out (see [RenderObject.performLayout]). See [RenderObject.markNeedsLayout]
/// for further details on marking an object dirty for layout.
///
/// 5. The compositing bits phase: The compositing bits on any dirty
/// [RenderObject] objects are updated. See
/// [RenderObject.markNeedsCompositingBitsUpdate].
///
/// 6. The paint phase: All the dirty [RenderObject]s in the system are
/// repainted (see [RenderObject.paint]). This generates the [Layer] tree. See
/// [RenderObject.markNeedsPaint] for further details on marking an object
/// dirty for paint.
///
/// 7. The compositing phase: The layer tree is turned into a [Scene] and
/// sent to the GPU.
///
/// 8. The semantics phase: All the dirty [RenderObject]s in the system have
/// their semantics updated (see [RenderObject.semanticsAnnotator]). This
/// generates the [SemanticsNode] tree. See
/// [RenderObject.markNeedsSemanticsUpdate] for further details on marking an
/// object dirty for semantics.
///
/// For more details on steps 4-8, see [PipelineOwner].
///
/// 9. The finalization phase in the widgets layer: The widgets tree is
/// finalized. This causes [State.dispose] to be invoked on any objects that
/// were removed from the widgets tree this frame. See
/// [BuildOwner.finalizeTree] for more details.
///
/// 10. The finalization phase in the scheduler layer: After [drawFrame]
/// returns, [handleDrawFrame] then invokes post-frame callbacks (registered
/// with [addPostFrameCallback]).
//
// When editing the above, also update rendering/binding.dart's copy.
@override
void drawFrame() {
assert(!debugBuildingDirtyElements);
assert(() {
debugBuildingDirtyElements = true;
return true;
}());
try {
if (renderViewElement != null)
buildOwner.buildScope(renderViewElement);
super.drawFrame();
buildOwner.finalizeTree();
} finally {
assert(() {
debugBuildingDirtyElements = false;
return true;
}());
}
if (!kReleaseMode) {
if (_needToReportFirstFrame && _reportFirstFrame) {
developer.Timeline.instantSync('Widgets completed first useful frame');
developer.postEvent('Flutter.FirstFrame', <String, dynamic>{});
_needToReportFirstFrame = false;
}
}
}
/// The [Element] that is at the root of the hierarchy (and which wraps the
/// [RenderView] object at the root of the rendering hierarchy).
///
/// This is initialized the first time [runApp] is called.
Element get renderViewElement => _renderViewElement;
Element _renderViewElement;
/// Takes a widget and attaches it to the [renderViewElement], creating it if
/// necessary.
///
/// This is called by [runApp] to configure the widget tree.
///
/// See also [RenderObjectToWidgetAdapter.attachToRenderTree].
void attachRootWidget(Widget rootWidget) {
_renderViewElement = RenderObjectToWidgetAdapter<RenderBox>(
container: renderView,
debugShortDescription: '[root]',
child: rootWidget,
).attachToRenderTree(buildOwner, renderViewElement);
}
/// Whether the [renderViewElement] has been initialized.
///
/// This will be false until [runApp] is called (or [WidgetTester.pumpWidget]
/// is called in the context of a [TestWidgetsFlutterBinding]).
bool get isRootWidgetAttached => _renderViewElement != null;
@override
Future<void> performReassemble() {
assert(() {
WidgetInspectorService.instance.performReassemble();
return true;
}());
deferFirstFrameReport();
if (renderViewElement != null)
buildOwner.reassemble(renderViewElement);
return super.performReassemble().then((void value) {
allowFirstFrameReport();
});
}
}
/// Inflate the given widget and attach it to the screen.
///
/// The widget is given constraints during layout that force it to fill the
/// entire screen. If you wish to align your widget to one side of the screen
/// (e.g., the top), consider using the [Align] widget. If you wish to center
/// your widget, you can also use the [Center] widget
///
/// Calling [runApp] again will detach the previous root widget from the screen
/// and attach the given widget in its place. The new widget tree is compared
/// against the previous widget tree and any differences are applied to the
/// underlying render tree, similar to what happens when a [StatefulWidget]
/// rebuilds after calling [State.setState].
///
/// Initializes the binding using [WidgetsFlutterBinding] if necessary.
///
/// See also:
///
/// * [WidgetsBinding.attachRootWidget], which creates the root widget for the
/// widget hierarchy.
/// * [RenderObjectToWidgetAdapter.attachToRenderTree], which creates the root
/// element for the element hierarchy.
/// * [WidgetsBinding.handleBeginFrame], which pumps the widget pipeline to
/// ensure the widget, element, and render trees are all built.
void runApp(Widget app) {
WidgetsFlutterBinding.ensureInitialized()
..attachRootWidget(app)
..scheduleWarmUpFrame();
}
/// Print a string representation of the currently running app.
void debugDumpApp() {
assert(WidgetsBinding.instance != null);
String mode = 'RELEASE MODE';
assert(() { mode = 'CHECKED MODE'; return true; }());
debugPrint('${WidgetsBinding.instance.runtimeType} - $mode');
if (WidgetsBinding.instance.renderViewElement != null) {
debugPrint(WidgetsBinding.instance.renderViewElement.toStringDeep());
} else {
debugPrint('<no tree currently mounted>');
}
}
/// A bridge from a [RenderObject] to an [Element] tree.
///
/// The given container is the [RenderObject] that the [Element] tree should be
/// inserted into. It must be a [RenderObject] that implements the
/// [RenderObjectWithChildMixin] protocol. The type argument `T` is the kind of
/// [RenderObject] that the container expects as its child.
///
/// Used by [runApp] to bootstrap applications.
class RenderObjectToWidgetAdapter<T extends RenderObject> extends RenderObjectWidget {
/// Creates a bridge from a [RenderObject] to an [Element] tree.
///
/// Used by [WidgetsBinding] to attach the root widget to the [RenderView].
RenderObjectToWidgetAdapter({
this.child,
this.container,
this.debugShortDescription,
}) : super(key: GlobalObjectKey(container));
/// The widget below this widget in the tree.
///
/// {@macro flutter.widgets.child}
final Widget child;
/// The [RenderObject] that is the parent of the [Element] created by this widget.
final RenderObjectWithChildMixin<T> container;
/// A short description of this widget used by debugging aids.
final String debugShortDescription;
@override
RenderObjectToWidgetElement<T> createElement() => RenderObjectToWidgetElement<T>(this);
@override
RenderObjectWithChildMixin<T> createRenderObject(BuildContext context) => container;
@override
void updateRenderObject(BuildContext context, RenderObject renderObject) { }
/// Inflate this widget and actually set the resulting [RenderObject] as the
/// child of [container].
///
/// If `element` is null, this function will create a new element. Otherwise,
/// the given element will have an update scheduled to switch to this widget.
///
/// Used by [runApp] to bootstrap applications.
RenderObjectToWidgetElement<T> attachToRenderTree(BuildOwner owner, [ RenderObjectToWidgetElement<T> element ]) {
if (element == null) {
owner.lockState(() {
element = createElement();
assert(element != null);
element.assignOwner(owner);
});
owner.buildScope(element, () {
element.mount(null, null);
});
} else {
element._newWidget = this;
element.markNeedsBuild();
}
return element;
}
@override
String toStringShort() => debugShortDescription ?? super.toStringShort();
}
/// A [RootRenderObjectElement] that is hosted by a [RenderObject].
///
/// This element class is the instantiation of a [RenderObjectToWidgetAdapter]
/// widget. It can be used only as the root of an [Element] tree (it cannot be
/// mounted into another [Element]; it's parent must be null).
///
/// In typical usage, it will be instantiated for a [RenderObjectToWidgetAdapter]
/// whose container is the [RenderView] that connects to the Flutter engine. In
/// this usage, it is normally instantiated by the bootstrapping logic in the
/// [WidgetsFlutterBinding] singleton created by [runApp].
class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObjectElement {
/// Creates an element that is hosted by a [RenderObject].
///
/// The [RenderObject] created by this element is not automatically set as a
/// child of the hosting [RenderObject]. To actually attach this element to
/// the render tree, call [RenderObjectToWidgetAdapter.attachToRenderTree].
RenderObjectToWidgetElement(RenderObjectToWidgetAdapter<T> widget) : super(widget);
@override
RenderObjectToWidgetAdapter<T> get widget => super.widget;
Element _child;
static const Object _rootChildSlot = Object();
@override
void visitChildren(ElementVisitor visitor) {
if (_child != null)
visitor(_child);
}
@override
void forgetChild(Element child) {
assert(child == _child);
_child = null;
}
@override
void mount(Element parent, dynamic newSlot) {
assert(parent == null);
super.mount(parent, newSlot);
_rebuild();
}
@override
void update(RenderObjectToWidgetAdapter<T> newWidget) {
super.update(newWidget);
assert(widget == newWidget);
_rebuild();
}
// When we are assigned a new widget, we store it here
// until we are ready to update to it.
Widget _newWidget;
@override
void performRebuild() {
if (_newWidget != null) {
// _newWidget can be null if, for instance, we were rebuilt
// due to a reassemble.
final Widget newWidget = _newWidget;
_newWidget = null;
update(newWidget);
}
super.performRebuild();
assert(_newWidget == null);
}
void _rebuild() {
try {
_child = updateChild(_child, widget.child, _rootChildSlot);
assert(_child != null);
} catch (exception, stack) {
final FlutterErrorDetails details = FlutterErrorDetails(
exception: exception,
stack: stack,
library: 'widgets library',
context: ErrorDescription('attaching to the render tree'),
);
FlutterError.reportError(details);
final Widget error = ErrorWidget.builder(details);
_child = updateChild(null, error, _rootChildSlot);
}
}
@override
RenderObjectWithChildMixin<T> get renderObject => super.renderObject;
@override
void insertChildRenderObject(RenderObject child, dynamic slot) {
assert(slot == _rootChildSlot);
assert(renderObject.debugValidateChild(child));
renderObject.child = child;
}
@override
void moveChildRenderObject(RenderObject child, dynamic slot) {
assert(false);
}
@override
void removeChildRenderObject(RenderObject child) {
assert(renderObject.child == child);
renderObject.child = null;
}
}
/// A concrete binding for applications based on the Widgets framework.
///
/// This is the glue that binds the framework to the Flutter engine.
class WidgetsFlutterBinding extends BindingBase with GestureBinding, ServicesBinding, SchedulerBinding, PaintingBinding, SemanticsBinding, RendererBinding, WidgetsBinding {
/// Returns an instance of the [WidgetsBinding], creating and
/// initializing it if necessary. If one is created, it will be a
/// [WidgetsFlutterBinding]. If one was previously initialized, then
/// it will at least implement [WidgetsBinding].
///
/// You only need to call this method if you need the binding to be
/// initialized before calling [runApp].
///
/// In the `flutter_test` framework, [testWidgets] initializes the
/// binding instance to a [TestWidgetsFlutterBinding], not a
/// [WidgetsFlutterBinding].
static WidgetsBinding ensureInitialized() {
if (WidgetsBinding.instance == null)
WidgetsFlutterBinding();
return WidgetsBinding.instance;
}
}