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abdullh.alsoleman
Front-End
Commits
8f0981c0
Unverified
Commit
8f0981c0
authored
Aug 09, 2022
by
Jonah Williams
Committed by
GitHub
Aug 09, 2022
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[framework] Animatable.fromCallback and code snippet (#108661)
parent
efbdb404
Changes
3
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3 changed files
with
78 additions
and
2 deletions
+78
-2
animation.dart
packages/flutter/lib/src/animation/animation.dart
+22
-2
tween.dart
packages/flutter/lib/src/animation/tween.dart
+24
-0
animation_from_listener_test.dart
.../flutter/test/animation/animation_from_listener_test.dart
+32
-0
No files found.
packages/flutter/lib/src/animation/animation.dart
View file @
8f0981c0
...
...
@@ -216,6 +216,23 @@ abstract class Animation<T> extends Listenable implements ValueListenable<T> {
/// ));
/// ```
/// {@end-tool}
/// {@tool snippet}
///
/// This method can be paired with an [Animatable] created via
/// [Animatable.fromCallback] in order to transform an animation with a
/// callback function. This can be useful for performing animations that
/// do not have well defined start or end points. This example transforms
/// the current scroll position into a color that cycles through values
/// of red.
///
/// ```dart
/// Animation<Color> _offset1 = Animation<double>.fromValueListenable(_scrollPosition)
/// .drive(Animatable<Color>.fromCallback((double value) {
/// return Color.fromRGBO(value.round() % 255, 0, 0, 1);
/// }));
/// ```
///
/// {@end-tool}
///
/// See also:
///
...
...
@@ -224,6 +241,8 @@ abstract class Animation<T> extends Listenable implements ValueListenable<T> {
/// * [CurvedAnimation], an alternative to [CurveTween] for applying easing
/// curves, which supports distinct curves in the forward direction and the
/// reverse direction.
/// * [Animatable.fromCallback], which allows creating an [Animatable] from an
/// arbitrary transformation.
@optionalTypeArgs
Animation
<
U
>
drive
<
U
>(
Animatable
<
U
>
child
)
{
assert
(
this
is
Animation
<
double
>);
...
...
@@ -266,8 +285,9 @@ abstract class Animation<T> extends Listenable implements ValueListenable<T> {
// An implementation of an animation that delegates to a value listenable with a fixed direction.
class
_ValueListenableDelegateAnimation
<
T
>
extends
Animation
<
T
>
{
_ValueListenableDelegateAnimation
(
this
.
_listenable
,
{
ValueListenableTransformer
<
T
>?
transformer
})
:
_transformer
=
transformer
;
_ValueListenableDelegateAnimation
(
this
.
_listenable
,
{
ValueListenableTransformer
<
T
>?
transformer
,
})
:
_transformer
=
transformer
;
final
ValueListenable
<
T
>
_listenable
;
final
ValueListenableTransformer
<
T
>?
_transformer
;
...
...
packages/flutter/lib/src/animation/tween.dart
View file @
8f0981c0
...
...
@@ -17,6 +17,10 @@ export 'curves.dart' show Curve;
// late Animation<Offset> _animation;
// late AnimationController _controller;
/// A typedef used by [Animatable.fromCallback] to create an [Animatable]
/// from a callback.
typedef
AnimatableCallback
<
T
>
=
T
Function
(
double
);
/// An object that can produce a value of type `T` given an [Animation<double>]
/// as input.
///
...
...
@@ -29,6 +33,14 @@ abstract class Animatable<T> {
/// const constructors so that they can be used in const expressions.
const
Animatable
();
/// Create a new [Animatable] from the provided [callback].
///
/// See also:
///
/// * [Animation.drive], which provides an example for how this can be
/// used.
const
factory
Animatable
.
fromCallback
(
AnimatableCallback
<
T
>
callback
)
=
_CallbackAnimatable
<
T
>;
/// Returns the value of the object at point `t`.
///
/// The value of `t` is nominally a fraction in the range 0.0 to 1.0, though
...
...
@@ -78,6 +90,18 @@ abstract class Animatable<T> {
}
}
// A concrete subclass of `Animatable` used by `Animatable.fromCallback`.
class
_CallbackAnimatable
<
T
>
extends
Animatable
<
T
>
{
const
_CallbackAnimatable
(
this
.
_callback
);
final
AnimatableCallback
<
T
>
_callback
;
@override
T
transform
(
double
t
)
{
return
_callback
(
t
);
}
}
class
_AnimatedEvaluation
<
T
>
extends
Animation
<
T
>
with
AnimationWithParentMixin
<
double
>
{
_AnimatedEvaluation
(
this
.
parent
,
this
.
_evaluatable
);
...
...
packages/flutter/test/animation/animation_from_listener_test.dart
View file @
8f0981c0
...
...
@@ -48,4 +48,36 @@ void main() {
expect
(
animation
.
value
,
1.0
);
});
test
(
'Animation created from ValueListenable can be transformed via drive'
,
()
{
final
ValueNotifier
<
double
>
listenable
=
ValueNotifier
<
double
>(
0.0
);
final
Animation
<
double
>
animation
=
Animation
<
double
>.
fromValueListenable
(
listenable
);
final
Animation
<
Offset
>
offset
=
animation
.
drive
(
Animatable
<
Offset
>.
fromCallback
((
double
value
)
{
return
Offset
(
0.0
,
value
);
}));
expect
(
offset
.
value
,
Offset
.
zero
);
expect
(
offset
.
status
,
AnimationStatus
.
forward
);
listenable
.
value
=
10
;
expect
(
offset
.
value
,
const
Offset
(
0.0
,
10.0
));
bool
listenerCalled
=
false
;
void
listener
()
{
listenerCalled
=
true
;
}
offset
.
addListener
(
listener
);
listenable
.
value
=
0.5
;
expect
(
listenerCalled
,
true
);
listenerCalled
=
false
;
offset
.
removeListener
(
listener
);
listenable
.
value
=
0.2
;
expect
(
listenerCalled
,
false
);
});
}
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