WidgetsBinding mixin

The glue between the widgets layer and the Flutter engine.

The WidgetsBinding manages a single Element tree rooted at rootElement. Calling runApp (which indirectly calls attachRootWidget) bootstraps that element tree.

Relationship to render trees

Multiple render trees may be associated with the element tree. Those are managed by the underlying RendererBinding.

The element tree is segmented into two types of zones: rendering zones and non-rendering zones.

A rendering zone is a part of the element tree that is backed by a render tree and it describes the pixels that are drawn on screen. For elements in this zone, Element.renderObject never returns null because the elements are all associated with RenderObjects. Almost all widgets can be placed in a rendering zone; notable exceptions are the View widget, ViewCollection widget, and RootWidget.

A non-rendering zone is a part of the element tree that is not backed by a render tree. For elements in this zone, Element.renderObject returns null because the elements are not associated with any RenderObjects. Only widgets that do not produce a RenderObject can be used in this zone because there is no render tree to attach the render object to. In other words, RenderObjectWidgets cannot be used in this zone. Typically, one would find InheritedWidgets, Views, and ViewCollections in this zone to inject data across rendering zones into the tree and to organize the rendering zones (and by extension their associated render trees) into a unified element tree.

The root of the element tree at rootElement starts a non-rendering zone. Within a non-rendering zone, the View widget is used to start a rendering zone by bootstrapping a render tree. Within a rendering zone, the ViewAnchor can be used to start a new non-rendering zone.

To figure out if an element is in a rendering zone it may walk up the tree calling Element.debugExpectsRenderObjectForSlot on its ancestors. If it reaches an element that returns false, it is in a non-rendering zone. If it reaches a RenderObjectElement ancestor it is in a rendering zone.

Superclass constraints

Mixin applications

Properties

accessibilityFeatures → AccessibilityFeatures: The currently active set of ui.AccessibilityFeatures.
no setterinherited
accessibilityFocus → ValueNotifier<int?>: Listenable that notifies when the accessibility focus on the system have changed.
finalinherited
buildOwner → BuildOwner?: The BuildOwner in charge of executing the build pipeline for the widget tree rooted at this binding.
no setter
channelBuffers → ChannelBuffers: The low level buffering and dispatch mechanism for messages sent by plugins on the engine side to their corresponding plugin code on the framework side.
no setterinherited
currentFrameTimeStamp → Duration: The time stamp for the frame currently being processed.
no setterinherited
currentSystemFrameTimeStamp → Duration: The raw time stamp as provided by the engine to dart:ui.PlatformDispatcher.onBeginFrame for the frame currently being processed.
no setterinherited
debugBuildingDirtyElements ↔ bool: Whether we are currently in a frame. This is used to verify that frames are not scheduled redundantly.
getter/setter pair
debugDidSendFirstFrameEvent → bool: Whether the first frame has finished building.
no setter
debugOutstandingSemanticsHandles → int: The number of clients registered to listen for semantics.
no setterinherited
debugSamplingClock → SamplingClock?: Overrides the sampling clock for debugging and testing.
no setterinherited
debugShowWidgetInspectorOverride ↔ bool: If true, forces the widget inspector to be visible.
getter/setter pair
debugShowWidgetInspectorOverrideNotifier → ValueNotifier<bool>: Notifier for debugShowWidgetInspectorOverride.
no setter
defaultBinaryMessenger → BinaryMessenger: The default instance of BinaryMessenger.
no setterinherited
disableAnimations → bool: The platform is requesting that animations be disabled or simplified.
no setterinherited
endOfFrame → Future<void>: Returns a Future that completes after the frame completes.
no setterinherited
firstFrameRasterized → bool: Whether the Flutter engine has rasterized the first frame.
no setter
focusManager → FocusManager: The object in charge of the focus tree.
no setter
framesEnabled → bool: Whether frames are currently being scheduled when scheduleFrame is called.
no setteroverride
gestureArena → GestureArenaManager: The gesture arenas used for disambiguating the meaning of sequences of pointer events.
finalinherited
hashCode → int: The hash code for this object.
no setterinherited
hasScheduledFrame → bool: Whether this scheduler has requested that handleBeginFrame be called soon.
no setterinherited
isRootWidgetAttached → bool: Whether the rootElement has been initialized.
no setter
keyboard → HardwareKeyboard: The global singleton instance of HardwareKeyboard, which can be used to query keyboard states.
no setterinherited
keyEventManager → KeyEventManager: The global singleton instance of KeyEventManager, which is used internally to dispatch key messages.
no setterinherited
lifecycleState → AppLifecycleState?: Whether the application is visible, and if so, whether it is currently interactive.
no setterinherited
locked → bool: Whether lockEvents is currently locking events.
no setterinherited
mouseTracker → MouseTracker: The object that manages state about currently connected mice, for hover notification.
no setterinherited
pipelineOwner → PipelineOwner: Deprecated. Will be removed in a future version of Flutter.
latefinalinherited
platformDispatcher → PlatformDispatcher: The ui.PlatformDispatcher to which this binding is bound.
no setterinherited
platformMenuDelegate ↔ PlatformMenuDelegate: A delegate that communicates with a platform plugin for serializing and managing platform-rendered menu bars created by PlatformMenuBar.
getter/setter pair
pointerRouter → PointerRouter: A router that routes all pointer events received from the engine.
finalinherited
pointerSignalResolver → PointerSignalResolver: The resolver used for determining which widget handles a PointerSignalEvent.
finalinherited
renderView → RenderView: Deprecated. Will be removed in a future version of Flutter.
latefinalinherited
renderViewElement → Element?: Deprecated. Will be removed in a future version of Flutter.
no setter
renderViews → Iterable<RenderView>: The RenderViews managed by this binding.
no setterinherited
resamplingEnabled ↔ bool: Enable pointer event resampling for touch devices by setting this to true.
getter/setter pairinherited
restorationManager → RestorationManager: The RestorationManager synchronizes the restoration data between engine and framework.
no setterinherited
rootElement → Element?: The Element that is at the root of the element tree hierarchy.
no setter
rootPipelineOwner → PipelineOwner: The PipelineOwner that is the root of the PipelineOwner tree.
no setterinherited
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
samplingClock → SamplingClock: Provides access to the current DateTime and StopWatch objects for sampling.
no setterinherited
samplingOffset ↔ Duration: Offset relative to current frame time that should be used for resampling. The samplingOffset is expected to be negative. Non-negative samplingOffset is allowed but will effectively disable resampling.
getter/setter pairinherited
schedulerPhase → SchedulerPhase: The phase that the scheduler is currently operating under.
no setterinherited
schedulingStrategy ↔ SchedulingStrategy: The strategy to use when deciding whether to run a task or not.
getter/setter pairinherited
semanticsEnabled → bool: Whether semantics information must be collected.
no setterinherited
sendFramesToEngine → bool: Whether frames produced by drawFrame are sent to the engine.
no setterinherited
transientCallbackCount → int: The current number of transient frame callbacks scheduled.
no setterinherited
waitUntilFirstFrameRasterized → Future<void>: A future that completes when the Flutter engine has rasterized the first frame.
no setter
window → SingletonFlutterWindow: Deprecated. Will be removed in a future version of Flutter.
no setterinherited

Methods

addObserver(WidgetsBindingObserver observer) → void: 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.
addPersistentFrameCallback(FrameCallback callback) → void: Adds a persistent frame callback.
inherited
addPostFrameCallback(FrameCallback callback, {String debugLabel = 'callback'}) → void: Schedule a callback for the end of this frame.
inherited
addRenderView(RenderView view) → void: Adds a RenderView to this binding.
inherited
addSemanticsEnabledListener(VoidCallback listener) → void: Adds a listener to be called when semanticsEnabled changes.
inherited
addTimingsCallback(TimingsCallback callback) → void: Add a TimingsCallback that receives FrameTiming sent from the engine.
inherited
allowFirstFrame() → void: Called after deferFirstFrame to tell the framework that it is ok to send the first frame to the engine now.
inherited
attachRootWidget(Widget rootWidget) → void: Takes a widget and attaches it to the rootElement, creating it if necessary.
attachToBuildOwner(RootWidget widget) → void: Called by attachRootWidget to attach the provided RootWidget to the buildOwner.
cancelFrameCallbackWithId(int id) → void: Cancels the transient frame callback with the given id.
inherited
cancelPointer(int pointer) → void: Dispatch a PointerCancelEvent for the given pointer soon.
inherited
computePlatformResolvedLocale(List<Locale> supportedLocales) → Locale?: Computes the locale the current platform would resolve to.
createBinaryMessenger() → BinaryMessenger: Creates a default BinaryMessenger instance that can be used for sending platform messages.
inherited
createCanvas(PictureRecorder recorder) → Canvas: Create a Canvas from a PictureRecorder.
inherited
createPictureRecorder() → PictureRecorder: Create a PictureRecorder.
inherited
createRestorationManager() → RestorationManager: Creates the RestorationManager instance available via restorationManager.
inherited
createRootPipelineOwner() → PipelineOwner: Creates the PipelineOwner that serves as the root of the pipeline owner tree (rootPipelineOwner).
inherited
createSceneBuilder() → SceneBuilder: Create a SceneBuilder.
inherited
createSemanticsUpdateBuilder() → SemanticsUpdateBuilder: Creates an empty semantics update builder.
inherited
createViewConfigurationFor(RenderView renderView) → ViewConfiguration: Returns a ViewConfiguration configured for the provided RenderView based on the current environment.
inherited
debugAssertNoPendingPerformanceModeRequests(String reason) → bool: Asserts that there are no pending performance mode requests in debug mode.
inherited
debugAssertNoTimeDilation(String reason) → bool: Asserts that there is no artificial time dilation in debug mode.
inherited
debugAssertNoTransientCallbacks(String reason) → bool: Asserts that there are no registered transient callbacks; if there are, prints their locations and throws an exception.
inherited
debugCheckZone(String entryPoint) → bool: Checks that the current Zone is the same as that which was used to initialize the binding.
inherited
debugGetRequestedPerformanceMode() → DartPerformanceMode?: Returns the current DartPerformanceMode requested or null if no requests have been made.
inherited
deferFirstFrame() → void: Tell the framework to not send the first frames to the engine until there is a corresponding call to allowFirstFrame.
inherited
dispatchAccessibilityFeaturesChanged() → void: Notify all the observers that the active set of AccessibilityFeatures has changed (using WidgetsBindingObserver.didChangeAccessibilityFeatures), giving them the features argument.
dispatchEvent(PointerEvent event, HitTestResult? hitTestResult) → void: Dispatch an event to pointerRouter and the path of a hit test result.
inherited
dispatchLocalesChanged(List<Locale>? locales) → void: Notify all the observers that the locale has changed (using WidgetsBindingObserver.didChangeLocales), giving them the locales argument.
drawFrame() → void: Pump the build and rendering pipeline to generate a frame.
override
ensureFrameCallbacksRegistered() → void: Ensures callbacks for PlatformDispatcher.onBeginFrame and PlatformDispatcher.onDrawFrame are registered.
inherited
ensureSemantics() → SemanticsHandle: Creates a new SemanticsHandle and requests the collection of semantics information.
inherited
ensureVisualUpdate() → void: Schedules a new frame using scheduleFrame if this object is not currently producing a frame.
inherited
evict(String asset) → void: Called in response to the ext.flutter.evict service extension.
inherited
exitApplication(AppExitType exitType, [int exitCode = 0]) → Future<AppExitResponse>: Exits the application by calling the native application API method for exiting an application cleanly.
inherited
handleAccessibilityFeaturesChanged() → void: Called when the platform accessibility features change.
override
handleAppLifecycleStateChanged(AppLifecycleState state) → void: Called when the application lifecycle state changes.
override
handleBeginFrame(Duration? rawTimeStamp) → void: Called by the engine to prepare the framework to produce a new frame.
inherited
handleDrawFrame() → void: Called by the engine to produce a new frame.
inherited
handleEvent(PointerEvent event, HitTestEntry<HitTestTarget> entry) → void: Override this method to receive events.
inherited
handleEventLoopCallback() → bool: Execute the highest-priority task, if it is of a high enough priority.
inherited
handleLocaleChanged() → void: Called when the system locale changes.
handleMemoryPressure() → void: Called when the operating system notifies the application of a memory pressure situation.
override
handleMetricsChanged() → void: Called when the system metrics change.
override
handlePlatformBrightnessChanged() → void: Called when the platform brightness changes.
override
handlePointerEvent(PointerEvent event) → void: Dispatch an event to the targets found by a hit test on its position.
inherited
handlePopRoute() → Future<bool>: Called when the system pops the current route.
handlePushRoute(String route) → Future<bool>: Called when the host tells the app to push a new route onto the navigator.
handleRequestAppExit() → Future<AppExitResponse>: Handles any requests for application exit that may be received on the SystemChannels.platform method channel.
override
handleSystemMessage(Object systemMessage) → Future<void>: Handler called for messages received on the SystemChannels.system message channel.
inherited
handleTextScaleFactorChanged() → void: Called when the platform text scale factor changes.
override
handleViewFocusChanged(ViewFocusEvent event) → void: Called whenever the PlatformDispatcher receives a notification that the focus state on a view has changed.
override
hitTest(HitTestResult result, Offset position) → void: Deprecated. Use hitTestInView instead.
inherited
hitTestInView(HitTestResult result, Offset position, int viewId) → void: Determine which HitTestTarget objects are located at a given position in the specified view.
inherited
initializationComplete() → Future<void>: Alert the engine that the binding is registered. This instructs the engine to register its top level window handler on Windows. This signals that the app is able to process "System.requestAppExit" signals from the engine.
inherited
initInstances() → void: The initialization method. Subclasses override this method to hook into the platform and otherwise configure their services. Subclasses must call "super.initInstances()".
override
initLicenses() → void: Adds relevant licenses to the LicenseRegistry.
inherited
initMouseTracker([MouseTracker? tracker]) → void: Creates a MouseTracker which manages state about currently connected mice, for hover notification.
inherited
initServiceExtensions() → void: Called when the binding is initialized, to register service extensions.
override
lockEvents(Future<void> callback()) → Future<void>: Locks the dispatching of asynchronous events and callbacks until the callback's future completes.
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
performReassemble() → Future<void>: This method is called by reassembleApplication to actually cause the application to reassemble, e.g. after a hot reload.
override
performSemanticsAction(SemanticsActionEvent action) → void: Called whenever the platform requests an action to be performed on a SemanticsNode.
inherited
postEvent(String eventKind, Map<String, dynamic> eventData) → void: All events dispatched by a BindingBase use this method instead of calling developer.postEvent directly so that tests for BindingBase can track which events were dispatched by overriding this method.
inherited
readInitialLifecycleStateFromNativeWindow() → void: Initializes the lifecycleState with the dart:ui.PlatformDispatcher.initialLifecycleState.
inherited
reassembleApplication() → Future<void>: Cause the entire application to redraw, e.g. after a hot reload.
inherited
registerBoolServiceExtension({required String name, required AsyncValueGetter<bool> getter, required AsyncValueSetter<bool> setter}) → void: Registers a service extension method with the given name (full name "ext.flutter.name"), which takes a single argument "enabled" which can have the value "true" or the value "false" or can be omitted to read the current value. (Any value other than "true" is considered equivalent to "false". Other arguments are ignored.)
inherited
registerNumericServiceExtension({required String name, required AsyncValueGetter<double> getter, required AsyncValueSetter<double> setter}) → void: Registers a service extension method with the given name (full name "ext.flutter.name"), which takes a single argument with the same name as the method which, if present, must have a value that can be parsed by double.parse, and can be omitted to read the current value. (Other arguments are ignored.)
inherited
registerServiceExtension({required String name, required ServiceExtensionCallback callback}) → void: Registers a service extension method with the given name (full name "ext.flutter.name").
inherited
registerSignalServiceExtension({required String name, required AsyncCallback callback}) → void: Registers a service extension method with the given name (full name "ext.flutter.name"), which takes no arguments and returns no value.
inherited
registerStringServiceExtension({required String name, required AsyncValueGetter<String> getter, required AsyncValueSetter<String> setter}) → void: Registers a service extension method with the given name (full name "ext.flutter.name"), which optionally takes a single argument with the name "value". If the argument is omitted, the value is to be read, otherwise it is to be set. Returns the current value.
inherited
removeObserver(WidgetsBindingObserver observer) → bool: Unregisters the given observer. This should be used sparingly as it is relatively expensive (O(N) in the number of registered observers).
removeRenderView(RenderView view) → void: Removes a RenderView previously added with addRenderView from the binding.
inherited
removeSemanticsEnabledListener(VoidCallback listener) → void: Removes a listener added by addSemanticsEnabledListener.
inherited
removeTimingsCallback(TimingsCallback callback) → void: Removes a callback that was earlier added by addTimingsCallback.
inherited
requestPerformanceMode(DartPerformanceMode mode) → PerformanceModeRequestHandle?: Request a specific DartPerformanceMode.
inherited
resetEpoch() → void: Prepares the scheduler for a non-monotonic change to how time stamps are calculated.
inherited
resetFirstFrameSent() → void: Call this to pretend that no frames have been sent to the engine yet.
inherited
resetGestureBinding() → void: Reset states of GestureBinding.
inherited
resetInternalState() → void: Allows the test framework to reset the lifecycle state and framesEnabled back to their initial values.
override
scheduleAttachRootWidget(Widget rootWidget) → void: Schedules a Timer for attaching the root widget.
scheduleForcedFrame() → void: Schedules a new frame by calling dart:ui.PlatformDispatcher.scheduleFrame.
inherited
scheduleFrame() → void: If necessary, schedules a new frame by calling dart:ui.PlatformDispatcher.scheduleFrame.
inherited
scheduleFrameCallback(FrameCallback callback, {bool rescheduling = false}) → int: Schedules the given transient frame callback.
inherited
scheduleTask<T>(TaskCallback<T> task, Priority priority, {String? debugLabel, Flow? flow}) → Future<T>: Schedules the given task with the given priority.
inherited
scheduleWarmUpFrame() → void: Schedule a frame to run as soon as possible, rather than waiting for the engine to request a frame in response to a system "Vsync" signal.
inherited
setSystemUiChangeCallback(SystemUiChangeCallback? callback) → void: Sets the callback for the SystemChrome.systemUIChange method call received on the SystemChannels.platform channel.
inherited
toString() → String: A string representation of this object.
inherited
unlocked() → void: Called by lockEvents when events get unlocked.
inherited
wrapWithDefaultView(Widget rootWidget) → Widget: Used by runApp to wrap the provided rootWidget in the default View.

Operators

operator ==(Object other) → bool: The equality operator.
inherited

Static Properties

instance → WidgetsBinding: The current WidgetsBinding, if one has been created.
no setter