How to make hero widget fly below appBar and bottomBar widgets in route transition.
I had tried to warp other widgets with hero also but no luck.
During a transition, Flutter places the Hero's in the order they are found in the widget (element) tree; last one on top. So you might be able to organise your screen in such a way that, the app bar and bottom bar heros are found later in the tree than the body containing other heros. For example with a Stack:
Stack(
children: [
Body(),
Positioned(
top: 0,
left: 0,
right: 0,
child: AppBar(),
),
Positioned(
bottom: 0,
left: 0,
right: 0,
child: BottomBar(),
),
],
)
This relies on the implementation details of Flutter's heros, so it is rather hacky.
Another approach would be to copy Flutter's HeroController, Hero and related code and modify it to order the Hero OverlayEntries by a new "z-index" property of the Hero widget.
The Heros "fly" in the Navigator's Overlay. So yet another approach could be to place your app bar and bottom bar on top of the Navigator (for example with a Stack like above).
None of these are great of course.
Related
Description
How do you position a custom back button on the exact location where the back button usually would be in an app bar?
Is kToolbarHeight 4px off?
Goal
I fade in the original app bar as the bottom sheet is pushed to the top.
Currently I'm using a Stack widget that positions the back button with kToolbarHeight from the top, but apparently that doesn't really match (It's rather kToolbarHeight - 4px).
I use a custom implementation of a back button, but this problem persists with the original backButton widget too.
Stack(
children: [
Map(...),
const Positioned(
top: kToolbarHeight,
left: 4.0,
child: CustomBackButton(),
),
],
);
Groundwork
I've looked it up in the dev tools and the original source code but couldn't find a reliable constant nor anything helpful.
Try like this:
Give your CustomBackButton() widget the dimensions of a square of kToolbarHeight side.
Inside your Stack, add a SafeArea child, into which you position the CustomBackButton() in the top left corner. That should place it in the right position.
The UI I'm making usually starts with the bottom sliver scrolled all the way in, so that its top is at the top of the view. But also:
Needs an extra empty space at the top, in case the user wants to pull the content down so that they can reach it without moving their hand from the bottom of the phone (this is a really basic ergonomic feature and I think we should expect to see it become pretty common soon, first led by apps moving more of their key functionality to the bottom of the screen, EG, Firefox's url bar.) (Currently, I'm using the appBar sliver for this, but I can imagine a full solution not using that)
Might need extra empty space at the bottom, whenever the content in that bottom sliver wont be long enough to allow it to be scrolled in all the way. It will seem buggy and irregular otherwise. Ideally I'd impose a minHeight so that the bottom sliver will always at least as tall as the screen, but it's a sliver, so I'm pretty sure that's not possible/ugly-difficult.
The avenue I'm considering right now is, ScrollPhysics wrapper that modifies its ScrollMetrics so that maxExtent and minExtent are larger. As far as I can tell, this will allow the CustomScrollView (given this ScrollPhysics) to overscroll. It feels kinda messy though. It would be nice to know what determines maxExtent and minExtent in the first place and alter that.
Lacking better options, I went ahead with the plan, and made my own custom ScrollPhysics class that allows overscroll by the given amount, extra.
return CustomScrollView(
physics: _ExtraScrollPhysics(extra: 100 * MediaQuery.of(context).devicePixelRatio),
...
And _ExtraScrollPhysics is basically just an extended AlwaysScrollable with all of the methods that take ScrollMetrics overloaded to copy its contents into a ScrollMetric with a minScrollExtent that has been decreased by -extra, then passing it along to the superclass's version of the method. It turns out that adjusting the maxScrollExtent field wasn't necessary for the usecase I described!
This has one drawback, the overscroll glow indicator, on top, appears at the top of the content, rather than the top of the scroll view, which looks pretty bad. It looks like this might be fixable, but I'd far prefer a method where this wasn't an issue.
mako's solution is a good starting point but it does not work for mouse wheel scrolling, only includes overscroll at the top, and did not implement the solution to the glow indicator problem.
A more general solution
For web, use a Listener to detect PointerSignalEvents, and manually scroll the list with a ScrollController.
For mobile, listening for events is not needed.
Extend a ScrollPhysics class as mako suggested but use NeverScrollableScrollPhysics for web to prevent the physics from interfering with the manual scrolling. To fix the glow indicator problem for mobile, wrap your CustomScrollView in a ScrollConfiguration as provided by nioncode.
Add overscroll_physics.dart from the gist.
Add custom_glowing_overscroll_indicator.dart from the other gist.
GestureBinding.instance.pointerSignalResolver.register is used to prevent the scroll event from propogating up the widget tree.
Example
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:my_project/custom_glowing_overscroll_indicator.dart';
import 'package:my_project/overscroll_physics.dart';
class OverscrollList extends StatelessWidget {
final ScrollController _scrollCtrl = ScrollController();
final double _topOverscroll = 200;
final double _bottomOverscroll = 200;
void _scrollList(Offset offset) {
_scrollCtrl.jumpTo(
_scrollCtrl.offset + offset.dy,
);
}
#override
Widget build(BuildContext context) {
return Container(
height: 300,
decoration: BoxDecoration(border: Border.all(width: 1)),
child: Listener(
onPointerSignal: (PointerSignalEvent event) {
if (kIsWeb) {
GestureBinding.instance.pointerSignalResolver.register(event, (event) {
_scrollList((event as PointerScrollEvent).scrollDelta);
});
}
},
child: ScrollConfiguration(
behavior: OffsetOverscrollBehavior(
leadingPaintOffset: -_topOverscroll,
trailingPaintOffset: -_bottomOverscroll,
),
child: CustomScrollView(
controller: _scrollCtrl,
physics: kIsWeb
? NeverScrollableOverscrollPhysics(
overscrollStart: _topOverscroll,
overscrollEnd: _bottomOverscroll,
)
: AlwaysScrollableOverscrollPhysics(
overscrollStart: _topOverscroll,
overscrollEnd: _bottomOverscroll,
),
slivers: [
SliverToBoxAdapter(
child: Container(width: 400, height: 100, color: Colors.blue),
),
SliverToBoxAdapter(
child: Container(width: 400, height: 100, color: Colors.yellow),
),
SliverToBoxAdapter(
child: Container(width: 400, height: 100, color: Colors.red),
),
SliverToBoxAdapter(
child: Container(width: 400, height: 100, color: Colors.orange),
),
],
),
),
),
);
}
}
dartpad demo
Mobile result:
I have a Stack with two Columns.
First column contains contains only one child (1) with InteractiveViewer which has defined height (for example 250). It changes its content's zoom and translation based on scroll offset of SingleChildScrollView from second column. It shouldn't be pushed out of the screen while scrolling, so it's under the scroll view in a stack.
The second column have SingleChildScrollView with top padding (2) OR first view (3) that matches the (1) height.
Now I'd like to make the top padding (2) or view (3) not scroll the SingleChildScrollView but pass those touch events to InteractiveViewer. Doesn't matter whether the solution use padding or empty view, I just wanted to note here than what I want can be achieved with padding or view. I tried both but failed.
I tried the GestureDetector, IgnorePointer and AbsorbPointer, but seems like the SingleChildScrollView always get the touch events. I haven't found a way to make the top padding not scrollable too.
Basically I'd like to achieve something similar to the attached gif, except that I don't need the "Collapsing Header" text animation and app bar. Just pay attention to the mountains that hide below the scroll view. The scroll view should take entire screen once the scroll offset is equal padding/view height (250 in this example).
Is that possible somehow? My logic behind InteractiveViewer is way more complicated than the example provided below, I just simplified it to make the question easier to understand.
Stack(children: [
Column(
children: [
Container( // (1) Widget that should get the touch events
height: 250,
child: InteractiveViewer(...)
),
],
),
Column(
children: [
Expanded(
child: SingleChildScrollView(
padding: EdgeInsets.only(top: 250), // (2) Either not scrollable padding
child: Column(
children: [
Container(height: 250), // (3) or not scrollable first item
Container(...)
],
),
),
),
],
),
]);
I’m planing to make a simple game in Flutter and in order to do so, I need to detect if some Widgets in Stack overlap(their parts are above each other). Widgets will be moving all the time, so I need to run that check in some kind of a timer.
Any ideas? Nothing crosses my mind.
The timer
The timer problem you can solve with Timer class from dart-async native package. The snippet below creates a timer that at each 750 milliseconds will call a function named _myCallbackFunction. As an example the callback function can check if there is widget overlap.
Timer.periodic(Duration(milliseconds: 750), _myCallbackFunction);
The Stack overlap layout
You can use Positioned widget from flutter framework to control where your widgets will be placed on the stack.
Stack(
children: <Widget>[
Positioned(left: 5, top: 0, right: 0, bottom: 10, child: MyCustomWidget(), );
Positioned(left: 10, top: 10, right: 0, bottom: 0, child: MyCustomWidget(), );
]
);
How to check if there is overlap
Well the trick is state management. Assuming that we're using MyCustomWidget will be needed store the positional parameters of each MyCustomWidget on the stack and eventually check if there is widgets in the same position top, right, bottom, left.You can define your logic and I advise you to user MobX library to do a easy and powerful state management.
I implemented SlideTransition for a widget in flutter, and it slides in as expected. The issue is that before the animation is called, the space where the slider is going to be displayed later is empty.
How can I make the parent to give this space to other widgets in the layout until the moment that a slider comes into view?
I was thinking about giving a slider the initial height of zero, but then the widgets inside the slider would act funny as the height changes in sync with sliding. I wonder if there is a simpler way.
The parent is:
new Scaffold(
appBar: _appBar,
body: new Column(
children: <Widget>[
new Expanded(
child: _body;
}),
),
new SlideTransition(
position: _sliderPosition, //
child: _slider,
),
],
);
And the position is defined as:
_sliderPosition = new MaterialPointArcTween(
begin: const Offset(0.0, 1.0),
end: Offset.zero,
).animate(_animationController);
I solved this issue by replacing _slider with _buildSlider() which returns null until a slider is needed.
This is also better for performance as there is no need to render a slider if it's hidden.
Bumped into the same issue with a SlideTransition taking the full height during a vertical slide. In the end I achieved the slide effect by using a SizeTransition instead, and setting its axisAlignment property accordingly (-1, 0, 1 for top/center/bottom in my case).