Trackpad gestures can trigger GestureRecognizer
Summary
#Trackpad gestures on most platforms now send PointerPanZoom
sequences and
can trigger pan, drag, and scale GestureRecognizer
callbacks.
Context
#Scrolling on Flutter Desktop prior to version 3.3.0 used PointerScrollEvent
messages to represent discrete scroll deltas. This system worked well for mouse
scroll wheels, but wasn't a good fit for trackpad scrolling. Trackpad scrolling
is expected to cause momentum, which depends not only on the scroll deltas, but
also the timing of when fingers are released from the trackpad.
In addition, trackpad pinching-to-zoom could not be represented.
Three new PointerEvent
s have been introduced: PointerPanZoomStartEvent
,
PointerPanZoomUpdateEvent
, and PointerPanZoomEndEvent
.
Relevant GestureRecognizer
s have been updated to register interest in
trackpad gesture sequences, and will emit onDrag
, onPan
, and/or
onScale
callbacks in response to movements
of two or more fingers on the trackpad.
This means both that code designed only for touch interactions might trigger upon trackpad interaction, and that code designed to handle all desktop scrolling might now only trigger upon mouse scrolling, and not trackpad scrolling.
Description of change
#The Flutter engine has been updated on all possible platforms to recognize
trackpad gestures and send them to the framework as PointerPanZoom
events
instead of as PointerScrollSignal
events. PointerScrollSignal
events will
still be used to represent scrolling on a mouse wheel.
Depending on the platform and specific trackpad model, the new system might not
be used, if not enough data is provided to the Flutter engine by platform APIs.
This includes on Windows, where trackpad gesture support is dependent on the
trackpad's driver, and the Web platform, where not enough data is provided by
browser APIs, and trackpad scrolling must still
use the old PointerScrollSignal
system.
Developers should be prepared to receive both types of events and ensure their apps or packages handle them in the appropriate manner.
Listener
now has three new callbacks: onPointerPanZoomStart
,
onPointerPanZoomUpdate
, and onPointerPanZoomEnd
which can
be used to observe trackpad scrolling and zooming events.
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Listener(
onPointerSignal: (PointerSignalEvent event) {
if (event is PointerScrollEvent) {
debugPrint('mouse scrolled ${event.scrollDelta}');
}
},
onPointerPanZoomStart: (PointerPanZoomStartEvent event) {
debugPrint('trackpad scroll started');
},
onPointerPanZoomUpdate: (PointerPanZoomUpdateEvent event) {
debugPrint('trackpad scrolled ${event.panDelta}');
},
onPointerPanZoomEnd: (PointerPanZoomEndEvent event) {
debugPrint('trackpad scroll ended');
},
child: Container()
);
}
}
PointerPanZoomUpdateEvent
contains a pan
field to represent the cumulative
pan of the current gesture, a panDelta
field to represent the difference in
pan since the last event, a scale
event to represent the cumulative zoom
of the current gesture, and a rotation
event to
represent the cumulative rotation (in radians) of the current gesture.
GestureRecognizer
s now have methods to all the trackpad events from one
continuous trackpad gesture. Calling the addPointerPanZoom
method on a
GestureRecognizer
with a PointerPanZoomStartEvent
will cause the recognizer
to register its interest in that trackpad interaction, and resolve conflicts
between multiple GestureRecognizer
s that could potentially respond to the
gesture.
The following example shows the proper use of Listener
and GestureRecognizer
to respond to trackpad interactions.
void main() => runApp(Foo());
class Foo extends StatefulWidget {
late final PanGestureRecognizer recognizer;
@override
void initState() {
super.initState();
recognizer = PanGestureRecognizer()
..onStart = _onPanStart
..onUpdate = _onPanUpdate
..onEnd = _onPanEnd;
}
void _onPanStart(DragStartDetails details) {
debugPrint('onStart');
}
void _onPanUpdate(DragUpdateDetails details) {
debugPrint('onUpdate');
}
void _onPanEnd(DragEndDetails details) {
debugPrint('onEnd');
}
@override
Widget build(BuildContext context) {
return Listener(
onPointerDown: recognizer.addPointer,
onPointerPanZoomStart: recognizer.addPointerPanZoom,
child: Container()
);
}
}
When using GestureDetector
, this is done automatically, so code such as the
following example will issue its gesture update callbacks in response to both
touch and trackpad panning.
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return GestureDetector(
onPanStart: (details) {
debugPrint('onStart');
},
onPanUpdate: (details) {
debugPrint('onUpdate');
},
onPanEnd: (details) {
debugPrint('onEnd');
}
child: Container()
);
}
}
Migration guide
#Migration steps depend on whether you want each gesture interaction in your app to be usable via a trackpad, or whether it should be restricted to only touch and mouse usage.
For gesture interactions suitable for trackpad usage
#Using GestureDetector
#No change is needed, GestureDetector
automatically processes trackpad
gesture events and triggers callbacks if recognized.
Using GestureRecognizer
and Listener
#Ensure that onPointerPanZoomStart
is passed through to
each recognizer from the Listener
.
The addPointerPanZoom
method of `GestureRecognizer must be called
for it to show interest and start tracking each trackpad gesture.
Code before migration:
void main() => runApp(Foo());
class Foo extends StatefulWidget {
late final PanGestureRecognizer recognizer;
@override
void initState() {
super.initState();
recognizer = PanGestureRecognizer()
..onStart = _onPanStart
..onUpdate = _onPanUpdate
..onEnd = _onPanEnd;
}
void _onPanStart(DragStartDetails details) {
debugPrint('onStart');
}
void _onPanUpdate(DragUpdateDetails details) {
debugPrint('onUpdate');
}
void _onPanEnd(DragEndDetails details) {
debugPrint('onEnd');
}
@override
Widget build(BuildContext context) {
return Listener(
onPointerDown: recognizer.addPointer,
child: Container()
);
}
}
Code after migration:
void main() => runApp(Foo());
class Foo extends StatefulWidget {
late final PanGestureRecognizer recognizer;
@override
void initState() {
super.initState();
recognizer = PanGestureRecognizer()
..onStart = _onPanStart
..onUpdate = _onPanUpdate
..onEnd = _onPanEnd;
}
void _onPanStart(DragStartDetails details) {
debugPrint('onStart');
}
void _onPanUpdate(DragUpdateDetails details) {
debugPrint('onUpdate');
}
void _onPanEnd(DragEndDetails details) {
debugPrint('onEnd');
}
@override
Widget build(BuildContext context) {
return Listener(
onPointerDown: recognizer.addPointer,
onPointerPanZoomStart: recognizer.addPointerPanZoom,
child: Container()
);
}
}
Using raw Listener
#The following code using PointerScrollSignal will no longer be called upon all
desktop scrolling. PointerPanZoomUpdate
events should be captured to receive
trackpad gesture data.
Code before migration:
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Listener(
onPointerSignal: (PointerSignalEvent event) {
if (event is PointerScrollEvent) {
debugPrint('scroll wheel event');
}
}
child: Container()
);
}
}
Code after migration:
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Listener(
onPointerSignal: (PointerSignalEvent event) {
if (event is PointerScrollEvent) {
debugPrint('scroll wheel event');
}
},
onPointerPanZoomUpdate: (PointerPanZoomUpdateEvent event) {
debugPrint('trackpad scroll event');
}
child: Container()
);
}
}
Please note: Use of raw Listener
in this way could
cause conflicts with other gesture interactions as it
doesn't participate in the gesture disambiguation arena.
For gesture interactions not suitable for trackpad usage
#Using GestureDetector
#If using Flutter 3.3.0, RawGestureDetector
could be used
instead of GestureDetector
to ensure each GestureRecognizer
created
by the GestureDetector
has supportedDevices
set to
exclude PointerDeviceKind.trackpad
.
Starting in version 3.4.0, there is a supportedDevices
parameter
directly on GestureDetector
.
Code before migration:
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return GestureDetector(
onPanStart: (details) {
debugPrint('onStart');
},
onPanUpdate: (details) {
debugPrint('onUpdate');
},
onPanEnd: (details) {
debugPrint('onEnd');
}
child: Container()
);
}
}
Code after migration (Flutter 3.3.0):
// Example of code after the change.
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return RawGestureDetector(
gestures: {
PanGestureRecognizer:
GestureRecognizerFactoryWithHandlers<PanGestureRecognizer>(
() => PanGestureRecognizer(
supportedDevices: {
PointerDeviceKind.touch,
PointerDeviceKind.mouse,
PointerDeviceKind.stylus,
PointerDeviceKind.invertedStylus,
// Do not include PointerDeviceKind.trackpad
}
),
(recognizer) {
recognizer
..onStart = (details) {
debugPrint('onStart');
}
..onUpdate = (details) {
debugPrint('onUpdate');
}
..onEnd = (details) {
debugPrint('onEnd');
};
},
),
},
child: Container()
);
}
}
Code after migration: (Flutter 3.4.0):
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return GestureDetector(
supportedDevices: {
PointerDeviceKind.touch,
PointerDeviceKind.mouse,
PointerDeviceKind.stylus,
PointerDeviceKind.invertedStylus,
// Do not include PointerDeviceKind.trackpad
},
onPanStart: (details) {
debugPrint('onStart');
},
onPanUpdate: (details) {
debugPrint('onUpdate');
},
onPanEnd: (details) {
debugPrint('onEnd');
}
child: Container()
);
}
}
Using RawGestureRecognizer
#Explicitly ensure that supportedDevices
doesn't include PointerDeviceKind.trackpad
.
Code before migration:
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return RawGestureDetector(
gestures: {
PanGestureRecognizer:
GestureRecognizerFactoryWithHandlers<PanGestureRecognizer>(
() => PanGestureRecognizer(),
(recognizer) {
recognizer
..onStart = (details) {
debugPrint('onStart');
}
..onUpdate = (details) {
debugPrint('onUpdate');
}
..onEnd = (details) {
debugPrint('onEnd');
};
},
),
},
child: Container()
);
}
}
Code after migration:
// Example of code after the change.
void main() => runApp(Foo());
class Foo extends StatelessWidget {
@override
Widget build(BuildContext context) {
return RawGestureDetector(
gestures: {
PanGestureRecognizer:
GestureRecognizerFactoryWithHandlers<PanGestureRecognizer>(
() => PanGestureRecognizer(
supportedDevices: {
PointerDeviceKind.touch,
PointerDeviceKind.mouse,
PointerDeviceKind.stylus,
PointerDeviceKind.invertedStylus,
// Do not include PointerDeviceKind.trackpad
}
),
(recognizer) {
recognizer
..onStart = (details) {
debugPrint('onStart');
}
..onUpdate = (details) {
debugPrint('onUpdate');
}
..onEnd = (details) {
debugPrint('onEnd');
};
},
),
},
child: Container()
);
}
}
Using GestureRecognizer
and Listener
#After upgrading to Flutter 3.3.0, there won't be a change in behavior, as
addPointerPanZoom
must be called on each GestureRecognizer
to allow
it to track gestures. The following code won't receive pan gesture callbacks
when the trackpad is scrolled:
void main() => runApp(Foo());
class Foo extends StatefulWidget {
late final PanGestureRecognizer recognizer;
@override
void initState() {
super.initState();
recognizer = PanGestureRecognizer()
..onStart = _onPanStart
..onUpdate = _onPanUpdate
..onEnd = _onPanEnd;
}
void _onPanStart(DragStartDetails details) {
debugPrint('onStart');
}
void _onPanUpdate(DragUpdateDetails details) {
debugPrint('onUpdate');
}
void _onPanEnd(DragEndDetails details) {
debugPrint('onEnd');
}
@override
Widget build(BuildContext context) {
return Listener(
onPointerDown: recognizer.addPointer,
// recognizer.addPointerPanZoom is not called
child: Container()
);
}
}
Timeline
#Landed in version: 3.3.0-0.0.pre
In stable release: 3.3.0
References
#API documentation:
Design document:
Relevant issues:
Relevant PRs:
- Support trackpad gestures in framework
- iPad trackpad gestures
- Linux trackpad gestures
- Mac trackpad gestures
- Win32 trackpad gestures
- ChromeOS/Android trackpad gestures
除非另有说明,本文档之所提及适用于 Flutter 的最新稳定版本,本页面最后更新时间: 2024-10-09。 查看文档源码 或者 为本页面内容提出建议。