// 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' as ui show window; import 'dart:ui' show AppLifecycleState, Locale; 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 'framework.dart'; export 'dart:ui' show AppLifecycleState, Locale; /// Interface for classes that register with the Widgets layer binding. /// /// See [WidgetsBinding.addObserver] and [WidgetsBinding.removeObserver]. 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. bool didPopRoute() => false; /// Called when the application's dimensions change. For example, /// when a phone is rotated. void didChangeMetrics() { } /// Called when the system tells the app that the user's locale has /// changed. For example, if the user changes the system language /// settings. void didChangeLocale(Locale locale) { } /// Called when the system puts the app in the background or returns /// the app to the foreground. void didChangeAppLifecycleState(AppLifecycleState state) { } } /// The glue between the widgets layer and the Flutter engine. abstract class WidgetsBinding extends BindingBase implements GestureBinding, RendererBinding { @override void initInstances() { super.initInstances(); _instance = this; buildOwner.onBuildScheduled = _handleBuildScheduled; ui.window.onLocaleChanged = handleLocaleChanged; PlatformMessages.setJSONMessageHandler('flutter/navigation', _handleNavigationMessage); PlatformMessages.setStringMessageHandler('flutter/lifecycle', _handleLifecycleMessage); } /// 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(); registerSignalServiceExtension( name: 'debugDumpApp', callback: debugDumpApp ); registerBoolServiceExtension( name: 'showPerformanceOverlay', getter: () => WidgetsApp.showPerformanceOverlayOverride, setter: (bool value) { if (WidgetsApp.showPerformanceOverlayOverride == value) return; WidgetsApp.showPerformanceOverlayOverride = value; buildOwner.reassemble(renderViewElement); } ); } /// The [BuildOwner] in charge of executing the build pipeline for the /// widget tree rooted at this binding. BuildOwner get buildOwner => _buildOwner; final BuildOwner _buildOwner = new BuildOwner(); 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). 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). bool removeObserver(WidgetsBindingObserver observer) => _observers.remove(observer); /// Called when the system metrics change. /// /// Notifies all the observers using /// [WidgetsBindingObserver.didChangeMetrics]. /// /// See [ui.window.onMetricsChanged]. @override void handleMetricsChanged() { super.handleMetricsChanged(); for (WidgetsBindingObserver observer in _observers) observer.didChangeMetrics(); } /// Called when the system locale changes. /// /// Calls [dispatchLocaleChanged] to notify the binding observers. /// /// See [ui.window.onLocaleChanged]. void handleLocaleChanged() { dispatchLocaleChanged(ui.window.locale); } /// Notify all the observers that the locale has changed (using /// [WidgetsBindingObserver.didChangeLocale]), giving them the /// `locale` argument. void dispatchLocaleChanged(Locale locale) { for (WidgetsBindingObserver observer in _observers) observer.didChangeLocale(locale); } /// 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. /// /// [WidgetsApp] uses this in conjunction with a [Navigator] to /// cause the back button to close dialog boxes, return from modal /// pages, and so forth. void handlePopRoute() { for (WidgetsBindingObserver observer in _observers) { if (observer.didPopRoute()) return; } SystemNavigator.pop(); } Future<dynamic> _handleNavigationMessage(Map<String, dynamic> message) async { final String method = message['method']; if (method == 'popRoute') handlePopRoute(); // TODO(abarth): Handle 'pushRoute'. } /// Called when the application lifecycle state changes. /// /// Notifies all the observers using /// [WidgetsBindingObserver.didChangeAppLifecycleState]. void handleAppLifecycleStateChanged(AppLifecycleState state) { for (WidgetsBindingObserver observer in _observers) observer.didChangeAppLifecycleState(state); } Future<String> _handleLifecycleMessage(String message) async { switch (message) { case 'AppLifecycleState.paused': handleAppLifecycleStateChanged(AppLifecycleState.paused); break; case 'AppLifecycleState.resumed': handleAppLifecycleStateChanged(AppLifecycleState.resumed); break; } return null; } bool _needToReportFirstFrame = true; bool _thisFrameWasUseful = true; /// Tell the framework that the frame we are currently building /// should not be considered to be a useful first frame. /// /// This is used by [WidgetsApp] to report the first frame. // // TODO(ianh): This method should only be available in debug and profile modes. void preventThisFrameFromBeingReportedAsFirstFrame() { _thisFrameWasUseful = false; } void _handleBuildScheduled() { // If we're in the process of building dirty elements, then changes // should not trigger a new frame. assert(() { if (debugBuildingDirtyElements) { throw new 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; }); scheduleFrame(); } /// 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 [handleBeginFrame], 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 [ui.window.onBeginFrame], invokes all the transient frame callbacks /// registered with [scheduleFrameCallback] and [addFrameCallback], 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. /// /// [handleBeginFrame] then invokes all the persistent frame callbacks, of which /// the most notable is this method, [beginFrame], which proceeds as follows: /// /// 2. 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. /// /// 3. 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. /// /// 4. The compositing bits phase: The compositing bits on any dirty /// [RenderObject] objects are updated. See /// [RenderObject.markNeedsCompositingBitsUpdate]. /// /// 5. 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. /// /// 6. The compositing phase: The layer tree is turned into a [ui.Scene] and /// sent to the GPU. /// /// 7. 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 3-7, see [PipelineOwner]. /// /// 8. 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. /// /// 9. The finalization phase in the scheduler layer: After [beginFrame] /// returns, [handleBeginFrame] then invokes post-frame callbacks (registered /// with [addPostFrameCallback]. // // When editing the above, also update rendering/binding.dart's copy. @override void beginFrame() { assert(!debugBuildingDirtyElements); assert(() { debugBuildingDirtyElements = true; return true; }); try { if (renderViewElement != null) buildOwner.buildScope(renderViewElement); super.beginFrame(); buildOwner.finalizeTree(); } finally { assert(() { debugBuildingDirtyElements = false; return true; }); } // TODO(ianh): Following code should not be included in release mode, only profile and debug modes. // See https://github.com/dart-lang/sdk/issues/27192 if (_needToReportFirstFrame) { if (_thisFrameWasUseful) { developer.Timeline.instantSync('Widgets completed first useful frame'); developer.postEvent('Flutter.FirstFrame', <String, dynamic>{}); _needToReportFirstFrame = false; } else { _thisFrameWasUseful = true; } } } /// 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 = new RenderObjectToWidgetAdapter<RenderBox>( container: renderView, debugShortDescription: '[root]', child: rootWidget ).attachToRenderTree(buildOwner, renderViewElement); } @override void reassembleApplication() { _needToReportFirstFrame = true; preventThisFrameFromBeingReportedAsFirstFrame(); if (renderViewElement != null) buildOwner.reassemble(renderViewElement); super.reassembleApplication(); } } /// 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 /// /// 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) ..handleBeginFrame(null); } /// 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, RenderObjectWithChildMixin<T> container, this.debugShortDescription }) : container = container, super(key: new GlobalObjectKey(container)); /// The widget below this widget in the tree. 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() => new 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 = const 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) { FlutterError.reportError(new FlutterErrorDetails( exception: exception, stack: stack, library: 'widgets library', context: 'attaching to the render tree' )); Widget error = new ErrorWidget(exception); _child = updateChild(null, error, _rootChildSlot); } } @override RenderObjectWithChildMixin<T> get renderObject => super.renderObject; @override void insertChildRenderObject(RenderObject child, dynamic slot) { assert(slot == _rootChildSlot); 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 SchedulerBinding, GestureBinding, ServicesBinding, 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) new WidgetsFlutterBinding(); return WidgetsBinding.instance; } }