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}
}
<code_end>
<topic_end>
<topic_start>
prepare for animations
control of the animation timing requires an
AnimationController.
add the SingleTickerProviderStateMixin
to the MenuState class. then, declare and
instantiate an AnimationController.
<code_start>
class _MenuState extends State<Menu> with SingleTickerProviderStateMixin {
late AnimationController _staggeredController;
@override
void initState() {
super.initState();
_staggeredController = AnimationController(
vsync: this,
);
}
}
@override
void dispose() {
_staggeredController.dispose();
super.dispose();
}
}
<code_end>
the length of the delay before every animation is
up to you. define the animation delays,
individual animation durations, and the total
animation duration.
<code_start>
class _MenuState extends State<Menu> with SingleTickerProviderStateMixin {
static const _initialDelayTime = duration(milliseconds: 50);
static const _itemSlideTime = duration(milliseconds: 250);
static const _staggerTime = duration(milliseconds: 50);
static const _buttonDelayTime = duration(milliseconds: 150);
static const _buttonTime = duration(milliseconds: 500);
final _animationDuration = _initialDelayTime +
(_staggertime * _menuTitles.length) +
_buttonDelayTime +
_buttonTime;
}
<code_end>
in this case, all the animations are delayed by 50 ms.
after that, list items begin to appear.
each list item’s appearance is delayed by 50 ms after the
previous list item begins to slide in.
each list item takes 250 ms to slide from right to left.
after the last list item begins to slide in,
the button at the bottom waits another 150 ms to pop in.
the button animation takes 500 ms.
with each delay and animation duration defined,
the total duration is calculated so that it can be
used to calculate the individual animation times.
the desired animation times are shown in the following diagram:
to animate a value during a subsection of a larger animation,
flutter provides the interval class.
an interval takes a start time percentage and an end
time percentage. that interval can then be used to
animate a value between those start and end times,
instead of using the entire animation’s start and
end times. for example, given an animation that takes 1 second,
an interval from 0.2 to 0.5 would start at 200 ms
(20%) and end at 500 ms (50%).
declare and calculate each list item’s interval and the
bottom button interval.
<code_start>
class _MenuState extends State<Menu> with SingleTickerProviderStateMixin {
final List<Interval> _itemSlideIntervals = [];
late interval _buttonInterval;
@override
void initState() {
super.initState();
_createAnimationIntervals();
_staggeredController = AnimationController(
vsync: this,
duration: _animationDuration,
);
}
void _createAnimationIntervals() {
for (var i = 0; i < _menuTitles.length; ++i) {
final startTime = _initialDelayTime + (_staggertime * i);
final endTime = startTime + _itemSlideTime;
_itemSlideIntervals.add(
interval(
startTime.inMilliseconds / _animationDuration.inMilliseconds,
endTime.inMilliseconds / _animationDuration.inMilliseconds,
),
);
}
final buttonStartTime =
duration(milliseconds: (_menutitles.length * 50)) + _buttonDelayTime;
final buttonEndTime = buttonStartTime + _buttonTime;
_buttonInterval = interval(
buttonStartTime.inMilliseconds / _animationDuration.inMilliseconds,
buttonEndTime.inMilliseconds / _animationDuration.inMilliseconds,