Listener class

A widget that calls callbacks in response to common pointer events.

It listens to events that can construct gestures, such as when the pointer is pressed, moved, then released or canceled.

It does not listen to events that are exclusive to mouse, such as when the mouse enters, exits or hovers a region without pressing any buttons. For these events, use MouseRegion.

Rather than listening for raw pointer events, consider listening for higher-level gestures using GestureDetector.

Layout behavior

See BoxConstraints for an introduction to box layout models.

If it has a child, this widget defers to the child for sizing behavior. If it does not have a child, it grows to fit the parent instead.

This example makes a Container react to being touched, showing a count of the number of pointer downs and ups.

import 'package:flutter/widgets.dart';

// ...

int _downCounter = 0;
int _upCounter = 0;
double x = 0.0;
double y = 0.0;

void _incrementDown(PointerEvent details) {
  _updateLocation(details);
  setState(() {
    _downCounter++;
  });
}
void _incrementUp(PointerEvent details) {
  _updateLocation(details);
  setState(() {
    _upCounter++;
  });
}
void _updateLocation(PointerEvent details) {
  setState(() {
    x = details.position.dx;
    y = details.position.dy;
  });
}

@override
Widget build(BuildContext context) {
  return ConstrainedBox(
    constraints: new BoxConstraints.tight(Size(300.0, 200.0)),
    child: Listener(
      onPointerDown: _incrementDown,
      onPointerMove: _updateLocation,
      onPointerUp: _incrementUp,
      child: Container(
        color: Colors.lightBlueAccent,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text('You have pressed or released in this area this many times:'),
            Text(
              '$_downCounter presses\n$_upCounter releases',
              style: Theme.of(context).textTheme.display1,
            ),
            Text(
              'The cursor is here: (${x.toStringAsFixed(2)}, ${y.toStringAsFixed(2)})',
            ),
          ],
        ),
      ),
    ),
  );
}

To create a sample project with this code snippet, run:
flutter create --sample=widgets.Listener.1 mysample

// Flutter code sample for Listener

// This example makes a [Container] react to being touched, showing a count of
// the number of pointer downs and ups.

import 'package:flutter/material.dart';

import 'package:flutter/widgets.dart';

void main() => runApp(MyApp());

/// This Widget is the main application widget.
class MyApp extends StatelessWidget {
  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: Center(
          child: MyStatefulWidget(),
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  MyStatefulWidget({Key key}) : super(key: key);

  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  int _downCounter = 0;
  int _upCounter = 0;
  double x = 0.0;
  double y = 0.0;

  void _incrementDown(PointerEvent details) {
    _updateLocation(details);
    setState(() {
      _downCounter++;
    });
  }

  void _incrementUp(PointerEvent details) {
    _updateLocation(details);
    setState(() {
      _upCounter++;
    });
  }

  void _updateLocation(PointerEvent details) {
    setState(() {
      x = details.position.dx;
      y = details.position.dy;
    });
  }

  @override
  Widget build(BuildContext context) {
    return ConstrainedBox(
      constraints: BoxConstraints.tight(Size(300.0, 200.0)),
      child: Listener(
        onPointerDown: _incrementDown,
        onPointerMove: _updateLocation,
        onPointerUp: _incrementUp,
        child: Container(
          color: Colors.lightBlueAccent,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                  'You have pressed or released in this area this many times:'),
              Text(
                '$_downCounter presses\n$_upCounter releases',
                style: Theme.of(context).textTheme.display1,
              ),
              Text(
                'The cursor is here: (${x.toStringAsFixed(2)}, ${y.toStringAsFixed(2)})',
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Inheritance

Constructors

Listener({Key key, PointerDownEventListener onPointerDown, PointerMoveEventListener onPointerMove, @Deprecated('Use MouseRegion.onEnter instead. See MouseRegion.opaque for behavioral difference. ' 'This feature was deprecated after v1.10.14.') PointerEnterEventListener onPointerEnter, @Deprecated('Use MouseRegion.onExit instead. See MouseRegion.opaque for behavioral difference. ' 'This feature was deprecated after v1.10.14.') PointerExitEventListener onPointerExit, @Deprecated('Use MouseRegion.onHover instead. See MouseRegion.opaque for behavioral difference. ' 'This feature was deprecated after v1.10.14.') PointerHoverEventListener onPointerHover, PointerUpEventListener onPointerUp, PointerCancelEventListener onPointerCancel, PointerSignalEventListener onPointerSignal, HitTestBehavior behavior: HitTestBehavior.deferToChild, Widget child }): Creates a widget that forwards point events to callbacks. [...]
const

Properties

behavior → HitTestBehavior: How to behave during hit testing.
final
onPointerCancel → PointerCancelEventListener: Called when the input from a pointer that triggered an onPointerDown is no longer directed towards this receiver.
final
onPointerDown → PointerDownEventListener: Called when a pointer comes into contact with the screen (for touch pointers), or has its button pressed (for mouse pointers) at this widget's location.
final
onPointerEnter → PointerEnterEventListener: Called when a pointer enters the region for this widget. [...]
final
onPointerExit → PointerExitEventListener: Called when a pointer leaves the region for this widget. [...]
final
onPointerHover → PointerHoverEventListener: Called when a pointer that has not triggered an onPointerDown changes position. [...]
final
onPointerMove → PointerMoveEventListener: Called when a pointer that triggered an onPointerDown changes position.
final
onPointerSignal → PointerSignalEventListener: Called when a pointer signal occurs over this object.
final
onPointerUp → PointerUpEventListener: Called when a pointer that triggered an onPointerDown is no longer in contact with the screen.
final
hashCode → int: The hash code for this object. [...]
read-only, inherited
key → Key: Controls how one widget replaces another widget in the tree. [...]
final, inherited
runtimeType → Type: A representation of the runtime type of the object.
read-only, inherited

Methods

build(BuildContext context) → Widget: Describes the part of the user interface represented by this widget. [...]
override
createElement() → StatelessElement: 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. [...]
@protected, inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void: Add additional properties associated with the node. [...]
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a non-existent method or property is accessed. [...]
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.debug }) → String: Returns 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 ==(dynamic other) → bool: The equality operator. [...]
inherited