Listener class Null safety

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.

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

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.headline4,
            ),
            Text(
              'The cursor is here: (${x.toStringAsFixed(2)}, ${y.toStringAsFixed(2)})',
            ),
          ],
        ),
      ),
    ),
  );
}

Inheritance

Constructors

Listener({Key? key, PointerDownEventListener? onPointerDown, PointerMoveEventListener? onPointerMove, PointerUpEventListener? onPointerUp, PointerHoverEventListener? onPointerHover, 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
child → Widget?: The widget below this widget in the tree. [...]
final, inherited
hashCode → int: The hash code for this object. [...]
@nonVirtual, read-only, inherited
key → Key?: Controls how one widget replaces another widget in the tree. [...]
final, inherited
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
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
runtimeType → Type: A representation of the runtime type of the object.
read-only, inherited

Methods

createElement() → SingleChildRenderObjectElement: RenderObjectWidgets always inflate to a RenderObjectElement subclass.
inherited
createRenderObject(BuildContext context) → RenderPointerListener: Creates an instance of the RenderObject class that this RenderObjectWidget represents, using the configuration described by this RenderObjectWidget. [...]
override
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. [...]
override
didUnmountRenderObject(covariant RenderObject renderObject) → void: A render object previously associated with this widget has been removed from the tree. The given RenderObject will be of the same type as returned by this object's createRenderObject.
@protected, 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.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
updateRenderObject(BuildContext context, covariant RenderPointerListener renderObject) → void: Copies the configuration described by this RenderObjectWidget to the given RenderObject, which will be of the same type as returned by this object's createRenderObject. [...]
override

Operators

operator ==(Object other) → bool: The equality operator. [...]
@nonVirtual, inherited