buildTransitions method
- BuildContext context,
- Animation<
double> animation, - Animation<
double> secondaryAnimation, - Widget child,
Override this method to wrap the child
with one or more transition
widgets that define how the route arrives on and leaves the screen.
By default, the child (which contains the widget returned by buildPage) is not wrapped in any transition widgets.
The buildTransitions method, in contrast to buildPage, is called each time the Route's state changes while it is visible (e.g. if the value of canPop changes on the active route).
The buildTransitions method is typically used to define transitions
that animate the new topmost route's comings and goings. When the
Navigator pushes a route on the top of its stack, the new route's
primary animation
runs from 0.0 to 1.0. When the Navigator pops the
topmost route, e.g. because the use pressed the back button, the
primary animation runs from 1.0 to 0.0.
We've used PageRouteBuilder to demonstrate the buildTransitions method here. The body of an override of the buildTransitions method would be defined in the same way.
PageRouteBuilder<void>(
pageBuilder: (BuildContext context,
Animation<double> animation,
Animation<double> secondaryAnimation,
) {
return Scaffold(
appBar: AppBar(title: const Text('Hello')),
body: const Center(
child: Text('Hello World'),
),
);
},
transitionsBuilder: (
BuildContext context,
Animation<double> animation,
Animation<double> secondaryAnimation,
Widget child,
) {
return SlideTransition(
position: Tween<Offset>(
begin: const Offset(0.0, 1.0),
end: Offset.zero,
).animate(animation),
child: child, // child is the value returned by pageBuilder
);
},
)
When the Navigator pushes a route on the top of its stack, the
secondaryAnimation
can be used to define how the route that was on
the top of the stack leaves the screen. Similarly when the topmost route
is popped, the secondaryAnimation can be used to define how the route
below it reappears on the screen. When the Navigator pushes a new route
on the top of its stack, the old topmost route's secondaryAnimation
runs from 0.0 to 1.0. When the Navigator pops the topmost route, the
secondaryAnimation for the route below it runs from 1.0 to 0.0.
secondaryAnimation
. When this route disappears because a new route has
been pushed on top of it, it translates in the opposite direction of
the new route. Likewise when the route is exposed because the topmost
route has been popped off.
PageRouteBuilder<void>(
pageBuilder: (BuildContext context,
Animation<double> animation,
Animation<double> secondaryAnimation,
) {
return Scaffold(
appBar: AppBar(title: const Text('Hello')),
body: const Center(
child: Text('Hello World'),
),
);
},
transitionsBuilder: (
BuildContext context,
Animation<double> animation,
Animation<double> secondaryAnimation,
Widget child,
) {
return SlideTransition(
position: Tween<Offset>(
begin: const Offset(0.0, 1.0),
end: Offset.zero,
).animate(animation),
child: SlideTransition(
position: Tween<Offset>(
begin: Offset.zero,
end: const Offset(0.0, 1.0),
).animate(secondaryAnimation),
child: child,
),
);
},
)
In practice the secondaryAnimation
is used pretty rarely.
The arguments to this method are as follows:
context
: The context in which the route is being built.animation
: When the Navigator pushes a route on the top of its stack, the new route's primaryanimation
runs from 0.0 to 1.0. When the Navigator pops the topmost route this animation runs from 1.0 to 0.0.secondaryAnimation
: When the Navigator pushes a new route on the top of its stack, the old topmost route'ssecondaryAnimation
runs from 0.0 to 1.0. When the Navigator pops the topmost route, thesecondaryAnimation
for the route below it runs from 1.0 to 0.0.child
, the page contents, as returned by buildPage.
See also:
- buildPage, which is used to describe the actual contents of the page,
and whose result is passed to the
child
argument of this method.
Implementation
@override
Widget buildTransitions(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation, Widget child) {
_setAnimation(animation);
return FadeTransition(
opacity: _curvedAnimation!,
child: super.buildTransitions(context, animation, secondaryAnimation, child),
);
}