dart:async

Zone class

A zone represents an environment that remains stable across asynchronous calls.

Code is always executed in the context of a zone, available as Zone.current. The initial main function runs in the context of the default zone (Zone.root). Code can be run in a different zone using either runZoned, to create a new zone, or Zone.run to run code in the context of an existing zone which was created earlier using Zone.fork.

Developers can create a new zone that overrides some of the functionality of an existing zone. For example, custom zones can replace of modify the behavior of print, timers, microtasks or how uncaught errors are handled.

The Zone class is not subclassable, but users can provide custom zones by forking an existing zone (usually Zone.current) with a ZoneSpecification. This is similar to creating a new class that extends the base Zone class and that overrides some methods, except without actually creating a new class. Instead the overriding methods are provided as functions that explicitly take the equivalent of their own class, the "super" class and the this object as parameters.

Asynchronous callbacks always run in the context of the zone where they were scheduled. This is implemented using two steps:

1. the callback is first registered using one of registerCallback, registerUnaryCallback, or registerBinaryCallback. This allows the zone to record that a callback exists and potentially modify it (by returning a different callback). The code doing the registration (e.g., Future.then) also remembers the current zone so that it can later run the callback in that zone.
2. At a later point the registered callback is run in the remembered zone, using one of run, runUnary or runBinary.

This is all handled internally by the platform code and most users don't need to worry about it. However, developers of new asynchronous operations, provided by the underlying system or through native extensions, must follow the protocol to be zone compatible.

For convenience, zones provide bindCallback (and the corresponding bindUnaryCallback and bindBinaryCallback) to make it easier to respect the zone contract: these functions first invoke the corresponding register functions and then wrap the returned function so that it runs in the current zone when it is later asynchronously invoked.

Similarly, zones provide bindCallbackGuarded (and the corresponding bindUnaryCallbackGuarded and bindBinaryCallbackGuarded), when the callback should be invoked through Zone.runGuarded.

Properties

errorZone → Zone

read-only

The error zone is responsible for dealing with uncaught errors. [...]

hashCode → int

read-only, inherited

The hash code for this object. [...]

parent → Zone?

read-only

The parent zone of the this zone. [...]

runtimeType → Type

read-only, inherited

A representation of the runtime type of the object.

Methods

bindBinaryCallback<R, T1, T2>(R callback(T1 argument1, T2 argument2)) → ZoneBinaryCallback<R, T1, T2>

Registers the provided callback and returns a function that will execute in this zone. [...]

bindBinaryCallbackGuarded<T1, T2>(void callback(T1 argument1, T2 argument2)) → void Function(T1, T2)

Registers the provided callback and returns a function that will execute in this zone. [...]

bindCallback<R>(R callback()) → ZoneCallback<R>

Registers the provided callback and returns a function that will execute in this zone. [...]

bindCallbackGuarded(void callback()) → void Function()

Registers the provided callback and returns a function that will execute in this zone. [...]

bindUnaryCallback<R, T>(R callback(T argument)) → ZoneUnaryCallback<R, T>

Registers the provided callback and returns a function that will execute in this zone. [...]

bindUnaryCallbackGuarded<T>(void callback(T argument)) → void Function(T)

Registers the provided callback and returns a function that will execute in this zone. [...]

createPeriodicTimer(Duration period, void callback(Timer timer)) → Timer

Creates a periodic Timer where the callback is executed in this zone.

createTimer(Duration duration, void callback()) → Timer

Creates a Timer where the callback is executed in this zone.

errorCallback(Object error, StackTrace? stackTrace) → AsyncError?

Intercepts errors when added programmatically to a Future or Stream. [...]

fork({ZoneSpecification? specification, Map<Object?, Object?>? zoneValues}) → Zone

Creates a new zone as a child zone of this zone. [...]

handleUncaughtError(Object error, StackTrace stackTrace) → void

Handles uncaught asynchronous errors. [...]

inSameErrorZone(Zone otherZone) → bool

Whether this zone and otherZone are in the same error zone. [...]

noSuchMethod(Invocation invocation) → dynamic

inherited

Invoked when a non-existent method or property is accessed. [...]

print(String line) → void

Prints the given line. [...]

registerBinaryCallback<R, T1, T2>(R callback(T1 arg1, T2 arg2)) → ZoneBinaryCallback<R, T1, T2>

Registers the given callback in this zone. [...]

registerCallback<R>(R callback()) → ZoneCallback<R>

Registers the given callback in this zone. [...]

registerUnaryCallback<R, T>(R callback(T arg)) → ZoneUnaryCallback<R, T>

Registers the given callback in this zone. [...]

run<R>(R action()) → R

Executes action in this zone. [...]

runBinary<R, T1, T2>(R action(T1 argument1, T2 argument2), T1 argument1, T2 argument2) → R

Executes the given action with argument1 and argument2 in this zone. [...]

runBinaryGuarded<T1, T2>(void action(T1 argument1, T2 argument2), T1 argument1, T2 argument2) → void

Executes the given action with argument1 and argument2 in this zone and catches synchronous errors. [...]

runGuarded(void action()) → void

Executes the given action in this zone and catches synchronous errors. [...]

runUnary<R, T>(R action(T argument), T argument) → R

Executes the given action with argument in this zone. [...]

runUnaryGuarded<T>(void action(T argument), T argument) → void

Executes the given action with argument in this zone and catches synchronous errors. [...]

scheduleMicrotask(void callback()) → void

Runs callback asynchronously in this zone. [...]

toString() → String

inherited

A string representation of this object. [...]

Operators

operator ==(Object other) → bool

inherited

The equality operator. [...]

operator [](Object? key) → dynamic

Retrieves the zone-value associated with key. [...]

Static Properties

current → Zone

read-only

The zone that is currently active.

Constants

root → const Zone

The root zone. [...]

_rootZone