BlocListener<B extends BlocBase<S>, S extends Object> class

Takes a BlocWidgetListener and an optional bloc and invokes the listener in response to state changes in the bloc. It should be used for functionality that needs to occur only in response to a state change such as navigation, showing a SnackBar, showing a Dialog, etc... The listener is guaranteed to only be called once for each state change unlike the builder in BlocBuilder.

If the bloc parameter is omitted, BlocListener will automatically perform a lookup using BlocProvider and the current BuildContext.

BlocListener<BlocA, BlocAState>(
  listener: (context, state) {
    // do stuff here based on BlocA's state
  },
  child: Container(),
)

Only specify the bloc if you wish to provide a bloc that is otherwise not accessible via BlocProvider and the current BuildContext.

BlocListener<BlocA, BlocAState>(
  value: blocA,
  listener: (context, state) {
    // do stuff here based on BlocA's state
  },
  child: Container(),
)

An optional listenWhen can be implemented for more granular control over when listener is called. listenWhen will be invoked on each bloc state change. listenWhen takes the previous state and current state and must return a bool which determines whether or not the listener function will be invoked. The previous state will be initialized to the state of the bloc when the BlocListener is initialized. listenWhen is optional and if omitted, it will default to true.

BlocListener<BlocA, BlocAState>(
  listenWhen: (previous, current) {
    // return true/false to determine whether or not
    // to invoke listener with state
  },
  listener: (context, state) {
    // do stuff here based on BlocA's state
  },
  child: Container(),
)

Inheritance

• Object
• DiagnosticableTree
• Widget
• StatelessWidget
• BlocListener

Implemented types

• NestableBlocListener

Constructors

BlocListener({required BlocWidgetListener<S> listener, Key? key, B? bloc, BlocListenerCondition<S>? listenWhen, Widget? child})

Takes a BlocWidgetListener and an optional bloc and invokes the listener in response to state changes in the bloc. It should be used for functionality that needs to occur only in response to a state change such as navigation, showing a SnackBar, showing a Dialog, etc... The listener is guaranteed to only be called once for each state change unlike the builder in BlocBuilder.

const

Properties

bloc → B?

bloc that has the state. If it's null, it will be infered from BuildContext

final, inherited

child → Widget?

The widget which will be rendered as a descendant.

final, inherited

hashCode → int

The hash code for this object.

no setter, inherited

hasNoChild → bool

Given that the NestableBlocListener are used in a MultiBlocProvider The must not have a child each one. Then, the hasNoChild allows the MultiBlocProvider to check that they don't have them.

no setter, override

key → Key?

Controls how one widget replaces another widget in the tree.

final, inherited

listener → BlocWidgetListener<S>

Takes the BuildContext along with the bloc state and is responsible for executing in response to state changes.

final, inherited

listenWhen → BlocListenerCondition<S>?

Takes the previous state and the current state and is responsible for returning a bool which determines whether or not to call listener with the current state.

final, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

$use() → S

The $use method is a sugar syntax for the useBloc.

inherited

asDiagnosticsNode() → DiagnosticsNode

Generates a DiagnosticsNode for show the bloc states in the debugger.

override

build(BuildContext context) → Widget

Describes the part of the user interface represented by this widget.

inherited

createElement() → _StatelessHookElement

Creates a StatelessElement to manage this widget's location in the tree.

inherited

debugDescribeChildren() → List<DiagnosticsNode>

Returns a list of DiagnosticsNode objects describing this node's children.

inherited

debugFillProperties(DiagnosticPropertiesBuilder properties) → void

Add additional properties associated with the node.

inherited

listen() → void

Helps to subscribe to a bloc

override

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

onStateEmitted(BuildContext context, S previous, S state) → bool

The onStateEmitted method allows to customize the behavior of the implementation of the BlocWidget

inherited

toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode

Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.

inherited

toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) → String

A string representation of this object.

inherited

toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String

Returns a string representation of this node and its descendants.

inherited

toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String

Returns a one-line detailed description of the object.

inherited

toStringShort() → String

A short, textual description of this widget.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited