I'm using CompositedTransformTarget and CompositedTransformFollower to display an OverlayEntry. How can I position the CompositedTransformFollower relative to the CompositedTransformTarget, i.e. how can I align its bottom to the top-center of the target in order to display it horizontally centered above the target, while maintaining interactivity (i.e. hit tests on the child should work)?
I tried to calculate the offset to give to CompositedTransformFollower, but I cannot do the correct calculation, because at that time I don't have the size of the child.
Sample Code:
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(brightness: Brightness.light),
home: Scaffold(
appBar: AppBar(title: Text('test')),
body: Center(child: OverlayButton()),
),
);
}
}
class OverlayButton extends StatefulWidget {
#override
_OverlayButtonState createState() => _OverlayButtonState();
}
class _OverlayButtonState extends State<OverlayButton> {
OverlayEntry _overlayEntry;
final LayerLink _layerLink = LayerLink();
bool _overlayIsShown = false;
#override
void dispose() {
super.dispose();
if (_overlayIsShown) {
_hideOverlay();
}
}
void _showOverlay() {
if (_overlayIsShown) return;
_overlayEntry = _createOverlayEntry();
Overlay.of(context).insert(_overlayEntry);
_overlayIsShown = true;
}
void _hideOverlay() {
_overlayIsShown = false;
_overlayEntry.remove();
}
#override
Widget build(BuildContext context) {
return CompositedTransformTarget(
link: _layerLink,
child: RaisedButton(child: Text('Open Overlay'), onPressed: _showOverlay),
);
}
OverlayEntry _createOverlayEntry() {
RenderBox renderBox = context.findRenderObject();
var anchorSize = renderBox.size;
return OverlayEntry(builder: (context) {
// TODO: dynamically use the correct child width / height for
// positioning us correctly on top + centered on the anchor
var childWidth = 200.0;
var childHeight = 40.0;
var childOffset =
Offset(-(childWidth - anchorSize.width) / 2, -(childHeight));
return Row(
children: <Widget>[
CompositedTransformFollower(
link: _layerLink,
offset: childOffset,
child: RaisedButton(
child: Text('close'),
onPressed: _hideOverlay,
),
),
],
);
});
}
}
General answer:
It looks like we want to know the exact size of a child, before deciding where to place the child. There's a widget made for this purpose, called CustomSingleChildLayout. Also, if you need to layout multiple children, you should check out the slightly more complex version, CustomMultiChildLayout.
For this case:
First you need to insert a CustomSingleChildLayout in the OverlayEntry you are building, for example, I added 2 lines here:
OverlayEntry _createOverlayEntry() {
RenderBox renderBox = context.findRenderObject();
var anchorSize = renderBox.size;
return OverlayEntry(builder: (context) {
return CompositedTransformFollower(
link: _layerLink,
child: CustomSingleChildLayout( // # Added Line 1 #
delegate: MyDelegate(anchorSize), // # Added Line 2 #
child: RaisedButton(
child: Text('close'),
onPressed: _hideOverlay,
),
),
);
});
}
Then let's create a delegate that handles your business logic. Notice I've also created a parameter to take in your "anchorSize":
class MyDelegate extends SingleChildLayoutDelegate {
final Size anchorSize;
MyDelegate(this.anchorSize);
#override
BoxConstraints getConstraintsForChild(BoxConstraints constraints) {
// we allow our child to be smaller than parent's constraint:
return constraints.loosen();
}
#override
Offset getPositionForChild(Size size, Size childSize) {
print("my size: $size");
print("childSize: $childSize");
print("anchor size being passed in: $anchorSize}");
// todo: where to position the child? perform calculation here:
return Offset(anchorSize.width, childSize.height / 2);
}
#override
bool shouldRelayout(_) => true;
}
As you can see, in the getPositionForChild method, we are able to gather all the information needed for calculating an offset. After calculating, we can just return that offset and CustomSingleChildLayout will take care of the placement.
To expand on this idea, you probably don't even need CompositedTransformFollower anymore, you can just do a full-screen overlay and calculate the offset that way.
I have a Dismissible widget in my application that I drag down to dismiss. There is a requirement that the transparency of the Dismissible should increase the further it is dragged down. So it should look as if it is fading out as it is dismissed. If it were to be dragged back up, its transparency should decrease.
As a simple test I tried wrapping the Dismissible in a Listener and Opacity widget. The opacity value is set to a variable tracked in state. The Listener widget listens to the total "y" axis movement of the Dismissible and when it reaches a certain threshold, decreases the the opacity value tracked in state. See code below for example:
import 'package:flutter/material.dart';
class FadingDismissible extends StatefulWidget {
#override
_FadingDismissible createState() => _FadingDismissible();
}
class _FadingDismissible extends State<FadingDismissible> {
double _totalMovement = 0;
double _opacity;
#override
void initState() {
super.initState();
_opacity = 1.0;
}
_setOpacity(double opacityValue) {
setState(() {
_opacity = opacityValue;
});
}
#override
Widget build(BuildContext context) {
return Listener(
onPointerMove: (PointerMoveEvent event) {
_totalMovement += event.delta.dy;
if (_totalMovement > 200) {
_setOpacity(0.5);
}
},
onPointerUp: (PointerUpEvent event) {
_setOpacity(1.0);
_totalMovement = 0;
},
child: Opacity(
opacity: _opacity,
child: Dismissible(
direction: DismissDirection.down,
key: UniqueKey(),
onDismissed: (direction) {
Navigator.pop(context);
},
child: Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: () {},
),
body: Container(color: Colors.blue),
),
),
),
);
}
}
The issue is, whenever the state is set, the widget is re-built and the Dismissible jumps back to the top.
Right now I'm not sure of another way around this. Is there a way to change the transparency of a Dismissible widget as it is dragged? Or will I have to use a different widget altogether?
Thanks!
I think might be the closest if you do not want to create your own Dismissible widget:
class FadingDismissible extends StatefulWidget {
final String text;
FadingDismissible({#required this.text});
#override
_FadingDismissibleState createState() => _FadingDismissibleState();
}
class _FadingDismissibleState extends State<FadingDismissible> {
double opacity = 1.0;
StreamController<double> controller = StreamController<double>();
Stream stream;
double startPosition;
#override
void initState() {
super.initState();
stream = controller.stream;
}
#override
void dispose() {
super.dispose();
controller.close();
}
#override
Widget build(BuildContext context) {
return Dismissible(
key: GlobalKey(),
child: StreamBuilder(
stream: stream,
initialData: 1.0,
builder: (context, snapshot) {
return Listener(
child: Opacity(
opacity: snapshot.data,
child: Text(widget.text),
),
onPointerDown: (event) {
startPosition = event.position.dx;
},
onPointerUp: (event) {
opacity = 1.0;
controller.add(opacity);
},
onPointerMove: (details) {
if (details.position.dx > startPosition) {
var move = details.position.dx - startPosition;
move = move / MediaQuery.of(context).size.width;
opacity = 1 - move;
controller.add(opacity);
}
},
);
},
),
);
}
}
Here is another method, similar to the one posted by #Sneider but uses a ValueNotifier and ValueListenableBuilder instead of Stream and `StreamBuilder.
import 'package:flutter/material.dart';
class FadingDismissible extends StatefulWidget {
const FadingDismissible({Key? key}) : super(key: key);
#override
State<FadingDismissible> createState() => _FadingDismissibleState();
}
class _FadingDismissibleState extends State<FadingDismissible> {
final ValueNotifier<double> _opacity = ValueNotifier(1.0);
late double _startPosition;
#override
Widget build(BuildContext context) {
return Dismissible(
key: UniqueKey(),
child: Listener(
onPointerDown: (event) {
_startPosition = event.position.dx;
},
onPointerUp: (event) {
_opacity.value = 1.0;
},
onPointerMove: (event) {
if (event.position.dx < _startPosition) {
// Dismiss Left
var move = _startPosition - event.position.dx;
move = move / MediaQuery.of(context).size.width;
_opacity.value = 1.0 - move;
} else {
// Dismiss Right
var move = event.position.dx - _startPosition;
move = move / MediaQuery.of(context).size.width;
_opacity.value = 1.0 - move;
}
},
child: ValueListenableBuilder(
valueListenable: _opacity,
builder: (BuildContext context, double opacity, Widget? child) {
return Opacity(
opacity: opacity > 0.2 ? opacity : 0.2,
child: Container(
color: Colors.red,
width: 100,
height: 100,
),
);
},
),
),
);
}
}
I don't understand how LayoutBuilder is used to get the height of a Widget.
I need to display the list of Widgets and get their height so I can compute some special scroll effects. I am developing a package and other developers provide widget (I don't control them). I read that LayoutBuilder can be used to get height.
In very simple case, I tried to wrap Widget in LayoutBuilder.builder and put it in the Stack, but I always get minHeight 0.0, and maxHeight INFINITY. Am I misusing the LayoutBuilder?
EDIT: It seems that LayoutBuilder is a no go. I found the CustomSingleChildLayout which is almost a solution.
I extended that delegate, and I was able to get the height of widget in getPositionForChild(Size size, Size childSize) method. BUT, the first method that is called is Size getSize(BoxConstraints constraints) and as constraints, I get 0 to INFINITY because I'm laying these CustomSingleChildLayouts in a ListView.
My problem is that SingleChildLayoutDelegate getSize operates like it needs to return the height of a view. I don't know the height of a child at that moment. I can only return constraints.smallest (which is 0, the height is 0), or constraints.biggest which is infinity and crashes the app.
In the docs it even says:
...but the size of the parent cannot depend on the size of the child.
And that's a weird limitation.
To get the size/position of a widget on screen, you can use GlobalKey to get its BuildContext to then find the RenderBox of that specific widget, which will contain its global position and rendered size.
Just one thing to be careful of: That context may not exist if the widget is not rendered. Which can cause a problem with ListView as widgets are rendered only if they are potentially visible.
Another problem is that you can't get a widget's RenderBox during build call as the widget hasn't been rendered yet.
But what if I need to get the size during the build! What can I do?
There's one cool widget that can help: Overlay and its OverlayEntry.
They are used to display widgets on top of everything else (similar to stack).
But the coolest thing is that they are on a different build flow; they are built after regular widgets.
That have one super cool implication: OverlayEntry can have a size that depends on widgets of the actual widget tree.
Okay. But don't OverlayEntry requires to be rebuilt manually?
Yes, they do. But there's another thing to be aware of: ScrollController, passed to a Scrollable, is a listenable similar to AnimationController.
Which means you could combine an AnimatedBuilder with a ScrollController, it would have the lovely effect to rebuild your widget automatically on a scroll. Perfect for this situation, right?
Combining everything into an example:
In the following example, you'll see an overlay that follows a widget inside ListView and shares the same height.
import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';
class MyHomePage extends StatefulWidget {
const MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final controller = ScrollController();
OverlayEntry sticky;
GlobalKey stickyKey = GlobalKey();
#override
void initState() {
if (sticky != null) {
sticky.remove();
}
sticky = OverlayEntry(
builder: (context) => stickyBuilder(context),
);
SchedulerBinding.instance.addPostFrameCallback((_) {
Overlay.of(context).insert(sticky);
});
super.initState();
}
#override
void dispose() {
sticky.remove();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: ListView.builder(
controller: controller,
itemBuilder: (context, index) {
if (index == 6) {
return Container(
key: stickyKey,
height: 100.0,
color: Colors.green,
child: const Text("I'm fat"),
);
}
return ListTile(
title: Text(
'Hello $index',
style: const TextStyle(color: Colors.white),
),
);
},
),
);
}
Widget stickyBuilder(BuildContext context) {
return AnimatedBuilder(
animation: controller,
builder: (_,Widget child) {
final keyContext = stickyKey.currentContext;
if (keyContext != null) {
// widget is visible
final box = keyContext.findRenderObject() as RenderBox;
final pos = box.localToGlobal(Offset.zero);
return Positioned(
top: pos.dy + box.size.height,
left: 50.0,
right: 50.0,
height: box.size.height,
child: Material(
child: Container(
alignment: Alignment.center,
color: Colors.purple,
child: const Text("^ Nah I think you're okay"),
),
),
);
}
return Container();
},
);
}
}
Note:
When navigating to a different screen, call following otherwise sticky would stay visible.
sticky.remove();
This is (I think) the most straightforward way to do this.
Copy-paste the following into your project.
UPDATE: using RenderProxyBox results in a slightly more correct implementation, because it's called on every rebuild of the child and its descendants, which is not always the case for the top-level build() method.
NOTE: This is not exactly an efficient way to do this, as pointed by Hixie here. But it is the easiest.
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
typedef void OnWidgetSizeChange(Size size);
class MeasureSizeRenderObject extends RenderProxyBox {
Size? oldSize;
OnWidgetSizeChange onChange;
MeasureSizeRenderObject(this.onChange);
#override
void performLayout() {
super.performLayout();
Size newSize = child!.size;
if (oldSize == newSize) return;
oldSize = newSize;
WidgetsBinding.instance!.addPostFrameCallback((_) {
onChange(newSize);
});
}
}
class MeasureSize extends SingleChildRenderObjectWidget {
final OnWidgetSizeChange onChange;
const MeasureSize({
Key? key,
required this.onChange,
required Widget child,
}) : super(key: key, child: child);
#override
RenderObject createRenderObject(BuildContext context) {
return MeasureSizeRenderObject(onChange);
}
#override
void updateRenderObject(
BuildContext context, covariant MeasureSizeRenderObject renderObject) {
renderObject.onChange = onChange;
}
}
Then, simply wrap the widget whose size you would like to measure with MeasureSize.
var myChildSize = Size.zero;
Widget build(BuildContext context) {
return ...(
child: MeasureSize(
onChange: (size) {
setState(() {
myChildSize = size;
});
},
child: ...
),
);
}
So yes, the size of the parent cannot can depend on the size of the child if you try hard enough.
Personal anecdote - This is handy for restricting the size of widgets like Align, which likes to take up an absurd amount of space.
Here's a sample on how you can use LayoutBuilder to determine the widget's size.
Since LayoutBuilder widget is able to determine its parent widget's constraints, one of its use case is to be able to have its child widgets adapt to their parent's dimensions.
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
var dimension = 40.0;
increaseWidgetSize() {
setState(() {
dimension += 20;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(children: <Widget>[
Text('Dimension: $dimension'),
Container(
color: Colors.teal,
alignment: Alignment.center,
height: dimension,
width: dimension,
// LayoutBuilder inherits its parent widget's dimension. In this case, the Container in teal
child: LayoutBuilder(builder: (context, constraints) {
debugPrint('Max height: ${constraints.maxHeight}, max width: ${constraints.maxWidth}');
return Container(); // create function here to adapt to the parent widget's constraints
}),
),
]),
),
floatingActionButton: FloatingActionButton(
onPressed: increaseWidgetSize,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
Demo
Logs
I/flutter (26712): Max height: 40.0, max width: 40.0
I/flutter (26712): Max height: 60.0, max width: 60.0
I/flutter (26712): Max height: 80.0, max width: 80.0
I/flutter (26712): Max height: 100.0, max width: 100.0
Update: You can also use MediaQuery to achieve similar function.
#override
Widget build(BuildContext context) {
var screenSize = MediaQuery.of(context).size ;
if (screenSize.width > layoutSize){
return Widget();
} else {
return Widget(); /// Widget if doesn't match the size
}
}
Let me give you a widget for that
class SizeProviderWidget extends StatefulWidget {
final Widget child;
final Function(Size) onChildSize;
const SizeProviderWidget(
{Key? key, required this.onChildSize, required this.child})
: super(key: key);
#override
_SizeProviderWidgetState createState() => _SizeProviderWidgetState();
}
class _SizeProviderWidgetState extends State<SizeProviderWidget> {
#override
void initState() {
///add size listener for first build
_onResize();
super.initState();
}
void _onResize() {
WidgetsBinding.instance?.addPostFrameCallback((timeStamp) {
if (context.size is Size) {
widget.onChildSize(context.size!);
}
});
}
#override
Widget build(BuildContext context) {
///add size listener for every build uncomment the fallowing
///_onResize();
return widget.child;
}
}
EDIT
Just wrap the SizeProviderWidget with OrientationBuilder to make it respect the orientation of the device
I made this widget as a simple stateless solution:
class ChildSizeNotifier extends StatelessWidget {
final ValueNotifier<Size> notifier = ValueNotifier(const Size(0, 0));
final Widget Function(BuildContext context, Size size, Widget child) builder;
final Widget child;
ChildSizeNotifier({
Key key,
#required this.builder,
this.child,
}) : super(key: key) {}
#override
Widget build(BuildContext context) {
WidgetsBinding.instance.addPostFrameCallback(
(_) {
notifier.value = (context.findRenderObject() as RenderBox).size;
},
);
return ValueListenableBuilder(
valueListenable: notifier,
builder: builder,
child: child,
);
}
}
Use it like this
ChildSizeNotifier(
builder: (context, size, child) {
// size is the size of the text
return Text(size.height > 50 ? 'big' : 'small');
},
)
If I understand correctly, you want to measure the dimension of some arbitrary widgets, and you can wrap those widgets with another widget. In that case, the method in the this answer should work for you.
Basically the solution is to bind a callback in the widget lifecycle, which will be called after the first frame is rendered, from there you can access context.size. The catch is that you have to wrap the widget you want to measure within a stateful widget. And, if you absolutely need the size within build() then you can only access it in the second render (it's only available after the first render).
findRenderObject() returns the RenderBox which is used to give the size of the drawn widget and it should be called after the widget tree is built, so it must be used with some callback mechanism or addPostFrameCallback() callbacks.
class SizeWidget extends StatefulWidget {
#override
_SizeWidgetState createState() => _SizeWidgetState();
}
class _SizeWidgetState extends State<SizeWidget> {
final GlobalKey _textKey = GlobalKey();
Size textSize;
#override
void initState() {
super.initState();
WidgetsBinding.instance.addPostFrameCallback((_) => getSizeAndPosition());
}
getSizeAndPosition() {
RenderBox _cardBox = _textKey.currentContext.findRenderObject();
textSize = _cardBox.size;
setState(() {});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Size Position"),
),
body: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Text(
"Currern Size of Text",
key: _textKey,
textAlign: TextAlign.center,
style: TextStyle(fontSize: 22, fontWeight: FontWeight.bold),
),
SizedBox(
height: 20,
),
Text(
"Size - $textSize",
textAlign: TextAlign.center,
),
],
),
);
}
}
Output:
There is no direct way to calculate the size of the widget, so to find that we have to take the help of the context of the widget.
Calling context.size returns us the Size object, which contains the height and width of the widget. context.size calculates the render box of a widget and returns the size.
Checkout https://medium.com/flutterworld/flutter-how-to-get-the-height-of-the-widget-be4892abb1a2
In cases where you don't want to wait for a frame to get the size, but want to know it before including it in your tree:
The simplest way is to follow the example of the BuildOwner documentation.
With the following you can just do
final size = MeasureUtil.measureWidget(MyWidgetTree());
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
/// Small utility to measure a widget before actually putting it on screen.
///
/// This can be helpful e.g. for positioning context menus based on the size they will take up.
///
/// NOTE: Use sparingly, since this takes a complete layout and sizing pass for the subtree you
/// want to measure.
///
/// Compare https://api.flutter.dev/flutter/widgets/BuildOwner-class.html
class MeasureUtil {
static Size measureWidget(Widget widget, [BoxConstraints constraints = const BoxConstraints()]) {
final PipelineOwner pipelineOwner = PipelineOwner();
final _MeasurementView rootView = pipelineOwner.rootNode = _MeasurementView(constraints);
final BuildOwner buildOwner = BuildOwner(focusManager: FocusManager());
final RenderObjectToWidgetElement<RenderBox> element = RenderObjectToWidgetAdapter<RenderBox>(
container: rootView,
debugShortDescription: '[root]',
child: widget,
).attachToRenderTree(buildOwner);
try {
rootView.scheduleInitialLayout();
pipelineOwner.flushLayout();
return rootView.size;
} finally {
// Clean up.
element.update(RenderObjectToWidgetAdapter<RenderBox>(container: rootView));
buildOwner.finalizeTree();
}
}
}
class _MeasurementView extends RenderBox with RenderObjectWithChildMixin<RenderBox> {
final BoxConstraints boxConstraints;
_MeasurementView(this.boxConstraints);
#override
void performLayout() {
assert(child != null);
child!.layout(boxConstraints, parentUsesSize: true);
size = child!.size;
}
#override
void debugAssertDoesMeetConstraints() => true;
}
This creates an entirely new render tree separate from the main one, and wont be shown on your screen.
So for example
print(
MeasureUtil.measureWidget(
Directionality(
textDirection: TextDirection.ltr,
child: Row(
mainAxisSize: MainAxisSize.min,
children: const [
Icon(Icons.abc),
SizedBox(
width: 100,
),
Text("Moin Meister")
],
),
),
),
);
Would give you Size(210.0, 24.0)
Might be this could help
Tested on Flutter: 2.2.3
Copy Below code this in your project.
import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';
class WidgetSize extends StatefulWidget {
final Widget child;
final Function onChange;
const WidgetSize({
Key? key,
required this.onChange,
required this.child,
}) : super(key: key);
#override
_WidgetSizeState createState() => _WidgetSizeState();
}
class _WidgetSizeState extends State<WidgetSize> {
#override
Widget build(BuildContext context) {
SchedulerBinding.instance!.addPostFrameCallback(postFrameCallback);
return Container(
key: widgetKey,
child: widget.child,
);
}
var widgetKey = GlobalKey();
var oldSize;
void postFrameCallback(_) {
var context = widgetKey.currentContext;
if (context == null) return;
var newSize = context.size;
if (oldSize == newSize) return;
oldSize = newSize;
widget.onChange(newSize);
}
}
declare a variable to store Size
Size mySize = Size.zero;
Add following code to get the size:
child: WidgetSize(
onChange: (Size mapSize) {
setState(() {
mySize = mapSize;
print("mySize:" + mySize.toString());
});
},
child: ()
This is Remi's answer with null safety, since the edit queue is full, I have to post it here.
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key}) : super(key: key);
#override
MyHomePageState createState() => MyHomePageState();
}
class MyHomePageState extends State<MyHomePage> {
final controller = ScrollController();
OverlayEntry? sticky;
GlobalKey stickyKey = GlobalKey();
#override
void initState() {
sticky?.remove();
sticky = OverlayEntry(
builder: (context) => stickyBuilder(context),
);
SchedulerBinding.instance
.addPostFrameCallback((_) => Overlay.of(context)?.insert(sticky!));
super.initState();
}
#override
void dispose() {
sticky?.remove();
super.dispose();
}
#override
Widget build(BuildContext context) => Scaffold(
body: ListView.builder(
controller: controller,
itemBuilder: (context, index) {
if (index == 6) {
return Container(
key: stickyKey,
height: 100.0,
color: Colors.green,
child: const Text("I'm fat"),
);
}
return ListTile(
title: Text(
'Hello $index',
style: const TextStyle(color: Colors.white),
),
);
},
),
);
Widget stickyBuilder(BuildContext context) => AnimatedBuilder(
animation: controller,
builder: (_, Widget? child) {
final keyContext = stickyKey.currentContext;
if (keyContext != null) {
final box = keyContext.findRenderObject() as RenderBox;
final pos = box.localToGlobal(Offset.zero);
return Positioned(
top: pos.dy + box.size.height,
left: 50.0,
right: 50.0,
height: box.size.height,
child: Material(
child: Container(
alignment: Alignment.center,
color: Colors.purple,
child: const Text("Nah I think you're okay"),
),
),
);
}
return Container();
},
);
}
use the package: z_tools.
The steps:
1. change main file
void main() async {
runZoned(
() => runApp(
CalculateWidgetAppContainer(
child: Center(
child: LocalizedApp(delegate, MyApp()),
),
),
),
onError: (Object obj, StackTrace stack) {
print('global exception: obj = $obj;\nstack = $stack');
},
);
}
2. use in function
_Cell(
title: 'cal: Column-min',
callback: () async {
Widget widget1 = Column(
mainAxisSize: MainAxisSize.min,
children: [
Container(
width: 100,
height: 30,
color: Colors.blue,
),
Container(
height: 20.0,
width: 30,
),
Text('111'),
],
);
// size = Size(100.0, 66.0)
print('size = ${await getWidgetSize(widget1)}');
},
),
The easiest way is to use MeasuredSize it's a widget that calculates the size of it's child in runtime.
You can use it like so:
MeasuredSize(
onChange: (Size size) {
setState(() {
print(size);
});
},
child: Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
);
You can find it here: https://pub.dev/packages/measured_size
It's easy and still can be done in StatelessWidget.
class ColumnHeightWidget extends StatelessWidget {
#override
Widget build(BuildContext context) {
final scrollController = ScrollController();
final columnKey = GlobalKey();
_scrollToCurrentProgress(columnKey, scrollController);
return Scaffold(
body: SingleChildScrollView(
controller: scrollController,
child: Column(
children: [],
),
),
);
}
void _scrollToCurrentProgress(GlobalKey<State<StatefulWidget>> columnKey,
ScrollController scrollController) {
WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
final RenderBox renderBoxRed =
columnKey.currentContext.findRenderObject();
final height = renderBoxRed.size.height;
scrollController.animateTo(percentOfHeightYouWantToScroll * height,
duration: Duration(seconds: 1), curve: Curves.decelerate);
});
}
}
in the same manner you can calculate any widget child height and scroll to that position.
**Credit to #Manuputty**
class OrigChildWH extends StatelessWidget {
final Widget Function(BuildContext context, Size size, Widget? child) builder;
final Widget? child;
const XRChildWH({
Key? key,
required this.builder,
this.child,
}) : super(key: key);
#override
Widget build(BuildContext context) {
return OrientationBuilder(builder: (context, orientation) {
return ChildSizeNotifier(builder: builder);
});
}
}
class ChildSizeNotifier extends StatelessWidget {
final ValueNotifier<Size> notifier = ValueNotifier(const Size(0, 0));
final Widget Function(BuildContext context, Size size, Widget? child) builder;
final Widget? child;
ChildSizeNotifier({
Key? key,
required this.builder,
this.child,
}) : super(key: key);
#override
Widget build(BuildContext context) {
WidgetsBinding.instance!.addPostFrameCallback(
(_) {
notifier.value = (context.findRenderObject() as RenderBox).size;
},
);
return ValueListenableBuilder(
valueListenable: notifier,
builder: builder,
child: child,
);
}
}
**Simple to use:**
OrigChildWH(
builder: (context, size, child) {
//Your child here: mine:: Container()
return Container()
})