Flutter: Can't add ListView to example app - flutter

I'm having a hard time Googling my way out of this. I've created the default Flutter app that comes with the basic tutorial, and now I would like to add a ListView to it, like so:
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
// Column is also a layout widget. It takes a list of children and
// arranges them vertically. By default, it sizes itself to fit its
// children horizontally, and tries to be as tall as its parent.
//
// Invoke "debug painting" (press "p" in the console, choose the
// "Toggle Debug Paint" action from the Flutter Inspector in Android
// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
// to see the wireframe for each widget.
//
// Column has various properties to control how it sizes itself and
// how it positions its children. Here we use mainAxisAlignment to
// center the children vertically; the main axis here is the vertical
// axis because Columns are vertical (the cross axis would be
// horizontal).
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
ListView(
padding: const EdgeInsets.all(8),
children: <Widget>[
Container(
width: 50, // This changes nothing.
height: 50, // This changes nothing.
child: const Center(child: Text('Text entry'))
)
]
),
],
),
),
The only thing I've added, is the ListView widget.
The error that I receive is this:
════════ Exception caught by rendering library ═════════════════════════════════════════════════════
RenderBox was not laid out: RenderRepaintBoundary#d4bf6 relayoutBoundary=up3 NEEDS-PAINT
'package:flutter/src/rendering/box.dart':
Failed assertion: line 1687 pos 12: 'hasSize'
The relevant error-causing widget was:
Column file:///Users/user/code/project/lib/main.dart:77:16
════════════════════════════════════════════════════════════════════════════════════════════════════
Now, I've concluded that this has something to do with how the ListView is packed into its parent container, maybe that the rendering engine doesn't know how to handle the size of the list view, but I haven't been able to find information on how to actually fix it.

this is because the ListView by default wants to expand itself to fill available space. and cause you to wrap it with column it can't expand itself. you have two options here:
First is Wrap your Listview with Expanded widget. Expanded will take all the remaining available space for its child. for this option use below code:
Expanded(
child: ListView(
padding: const EdgeInsets.all(8),
children: <Widget>[
Container(
width: 50, // This changes nothing.
height: 50, // This changes nothing.
child: const Center(child: Text('Text entry'))
)
]
),
),
the second option is to set shrinkWrap property of ListView to true. by doing this ListView don't expand itself:
ListView(
shrinkWrap: true,
padding: const EdgeInsets.all(8),
children: <Widget>[
Container(
width: 50, // This changes nothing.
height: 50, // This changes nothing.
child: const Center(child: Text('Text entry'))
)
]
)

I think the problem comes from the fact that you place a ListView inside a Column. Hence you must provide a size to your ListView. the answer to this question provides a good code example to solve your issue.
The actual reason for this error is that both Column and ListView try to expands in vertical axis. hence you need to constrain the height of ListView.

listView has shrinkWrap attribute can you try:
ListView(
shrinkWrap: true,
padding: const EdgeInsets.all(8),
children: <Widget>[
Container(
width: 50, // This changes nothing.
height: 50, // This changes nothing.
child: const Center(child: Text('Text entry'))
)
]
)

Related

How to display a screen which contains of an Icon on top half and ListView on bottom half?

I want to display a mock-up streaming screen like this:
Top half is the video player (showing the speaker), and bottom half is a ListView displaying participants/subscribers list.
Here's my code:
import 'package:flutter/material.dart';
import 'common.dart';
class StreamingView extends StatelessWidget {
// Display a Participant item
Widget getParticipantView(Participant item) {
return Container(
padding: EdgeInsets.all(10.0),
child: Column(
children: [
Align(
alignment: Alignment.centerLeft,
child: Text(
item.name,
style: TextStyle(fontSize: 14, color: Colors.black54),
),
),
Expanded(
child: CircleAvatar(backgroundColor: Colors.blue),
),
],
));
}
// Display the participants list on a ListView
Widget getParticipantsListView(List<Participant> participantsList){
//#override
// Widget build(BuildContext context) {
return Container (
//Expanded()
height: 40,
child: ListView.builder(
itemCount: participantsList.length,
itemBuilder: (context, index){
return getParticipantView(participantsList[index]);
}
)
);
//}
}
#override
Widget build(context) {
List<Participant> theList = [
Participant(name: "Jack", description:"Away"),
Participant(name:"Paul", description:"Available"),
Participant(name:"Clive", description:"Available"),
Participant(name:"Frank", description:"Available")
];
return Scaffold(
appBar: AppBar(),
body: Container(
padding: EdgeInsets.all(10.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
Image.asset('assets/generic_portrait.jpg'),
Expanded(
flex: 1,
child: getParticipantsListView(theList)
),
],
)),
floatingActionButton: FloatingActionButton(
onPressed: () async {
print("The button is clicked...");
},
child: Icon(Icons.video_call)));
}
}
I ran it, and the result is this:
The speaker can be seen, but the participants list isn't. Turns out there's an exception:
══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY
╞═════════════════════════════════════════════════════════ The
following assertion was thrown during performLayout(): RenderFlex
children have non-zero flex but incoming height constraints are
unbounded. When a column is in a parent that does not provide a finite
height constraint, for example if it is in a vertical scrollable, it
will try to shrink-wrap its children along the vertical axis. Setting
a flex on a child (e.g. using Expanded) indicates that the child is to
expand to fill the remaining space in the vertical direction. These
two directives are mutually exclusive. If a parent is to shrink-wrap
its child, the child cannot simultaneously expand to fit its parent.
Consider setting mainAxisSize to MainAxisSize.min and using
FlexFit.loose fits for the flexible children (using Flexible rather
than Expanded). This will allow the flexible children to size
themselves to less than the infinite remaining space they would
otherwise be forced to take, and then will cause the RenderFlex to
shrink-wrap the children rather than expanding to fit the maximum
constraints provided by the parent. ... ... The relevant error-causing
widget was: Column
file:///C:/Users/anta40/Flutter/streamingtest/streaming.dart:11:16
That refers to child: Column( inside Widget getParticipantView().
How to fix this?
you can use stack , the parent maybe use column after that the stack will be the first , after that use a listview which can hold all the participants
Have you tried using Shrink-wrap in ListView.builder and remove the container with Static height.
The hight is unbound because you're using Expanded widget in the column. Remove the Expanded widget that is wrapping the CircleAvatar. Here's your code:
// Display a Participant item
Widget getParticipantView(Participant item) {
return Container(
padding: EdgeInsets.all(10.0),
child: Column(
children: [
Align(
alignment: Alignment.centerLeft,
child: Text(
item.name,
style: TextStyle(fontSize: 14, color: Colors.black54),
),
),
CircleAvatar(backgroundColor: Colors.blue),
],
));
}

In Flutter, how can I have an adjusting vertical layout, a mix between column and listview behavior?

As far as I see, Column and ListView both have a very distinct usage when used for a base root layouting.
Column is used when the screen has few components (such as login screen). We can add some Expanded components to adjust white spaces in between, so when the keyboard is visible, the screen shrink to keep everything visible.
ListView is used when the screen has many components that potentially need scrolling. We can't use Expanded component in ListView. When using ListView, appearing keyboard does not change the white spaces, only change the size of outer ListView, while the inner content is wrapped in scroll view.
Now the problem is, how if I want to have screen like this:
When all the contents' combined vertical size is not longer than available height quota given from parent (in this case, screen's height), then the components behave like inside Column: expanding or shrinking to fill available white spaces according to rules set by Expanded.
When all the content's combined vertical size is longer than available height quota, then the components behave like inside ListView: all the possible expanding components will shrink into their minimum size (ignoring Expanded), and the screen is scrollable so user can see the rest of the screen below.
Is this possible to be done in Flutter? How?
EDIT: based on Reign's comment, I have isolated some code from SingleChildScrollView manual, but it looks like it still can't handle if its children contains Expanded.
Widget columnRoot({
MainAxisAlignment mainAxisAlignment = MainAxisAlignment.spaceBetween,
AssetImage backgroundImage,
List<Widget> children
}) =>
LayoutBuilder(builder: (BuildContext context, BoxConstraints viewportConstraints) =>
SingleChildScrollView(
child: ConstrainedBox(
constraints: BoxConstraints(
minHeight: viewportConstraints.maxHeight,
),
child: Container(
decoration: BoxDecoration(
image: DecorationImage(
image: backgroundImage,
fit: BoxFit.cover),
color: Colors.white
),
child: Column(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: mainAxisAlignment,
children: children
),
)
)
)
);
Widget content(BuildContext context) => columnRoot(children: [
Container(color: Colors.red, height: 100.0),
Expanded(Container(color: Colors.green)), // without this line, there's no layout error
Container(color: Colors.blue, height: 100.0),
]);
Error:
RenderFlex children have non-zero flex but incoming height constraints are unbounded.
I added some code you can test with also with some explanation.
Copy paste and run the code
class MyWidget extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
child: SingleChildScrollView( //Since setting it to scrollable, your widget Column with expanded children wont work as it supposed to be because it wont know its parent height
//Since its already scrollable `Expanded` will expand or shrink now based on it child widget (Expanded(child: SomeHeight widget)) refer: #10 example
child: IntrinsicHeight( //This will fix the expanded widget error
child: Container(
//Test remove this height
// height: 400, //But when you set its height before its parent scroll widget, `Expanded` will expand based on its available space
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
mainAxisSize: MainAxisSize.max,
children: [
Container(color: Colors.red, height: 100.0),
//#10
//Experiment with this
Expanded(
child: Container(
color: Colors.purple,
// height: 100.0, //initialized height, remove parent container height: 400
// child: Text("This is also considered as min height"),
),
),
Container(color: Colors.blue, height: 100.0),
],
),
),
),
),
),
);
}
}

Flutter: How to adjust the height of a container as the maximum height of its sibling in a row

I have two widgets in a row. The first widget is a black line with width 5.0, the second widget is a text widget whose size may vary according to the content. I want the first container to have the same height as of the second widget
One way is to make both widget child of an IntrinsicHeight widget and then declare the height of the first container as double.infinity. This should solve your problem. Example code is given below:
IntrinsicHeight(
child: Row(
children: <Widget>[
Container( //this is the first container
height: double.infinity
),
secondWidget(
)
],
)
Let me know if you have further query. Happy coding!
You can use Expanded widget. It divides siblings to the same height or width.
here is the code:
Row(
children: <Widget>[
Expanded(
child: Container(
color: Colors.red,
),
),
Expanded(
child: Container(
color: Colors.green,
),
)
And here is the result:
That is so easy. I wish it could help.

TabBarView expanded till bottom irrespective of the start

I have been working on flutter, and now have to make the Tab Bar for the page. Since I've succeeded in making the tabs, but there is one thing which is not letting me complete my task which is this,
I have a design blueprint which is like this:
Column{
mainAxisSize: MainAxisSize.max,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <widget>[
Text("Hello World!"),
Container(child: TabWidget())
]
}
I have not given any specific height to the container of the TabWidget() since I wanted the Tabs to take up the full height till the bottom.
TabWidget
child: TabBar(
controller: _controller,
tabs: [
new Tab(
child: Padding(
padding: EdgeInsets.only(top: 18.0),
child: Text(""),
)
),
new Tab(
child: Padding(
padding: EdgeInsets.only(top: 18.0),
child: Text(""),
)
),
]
)
),
Container(
//Deifining the height here, not deifing it will hide the content of the tabs
height: MediaQuery.of(context).size.height/2.3,
child: new TabBarView(
controller: _controller,
children: <Widget>[
new Container(
padding: EdgeInsets.only(top: 15.0),
child: Listview(
scrollDirection: Axis.Vertical,
children: <Widget> [
...
]
)
),
new Container(
padding: EdgeInsets.only(top: 15.0),
child: Listview(
scrollDirection: Axis.Vertical,
children: <Widget> [
...
]
)
)
]
)
)
]
);
Here is the catch, now I have tried my level best to get the result and hence did this :
Use of Expanded() in the TabWidget to take up the height
Use of double.infinity() in the height element of TabBarView
I have read this answer : TabBarView without bounded height, but I don't want my screen to scrollable, Silver is not required in this case. Just the TabBarView should be expanded till the bottom irrespective of from where it is starting
I don't want to give a particular height to my TabBarView, instead, I want it to take the full height till the bottom irrespective of the screen, so my height is dynamic as per the screen.
I'd like to get some inputs on this so that I'd achieve my point. I'm using ListView() in the child of TabBarView, so even if the portion size is small of the screen of the phone user will still be able to scroll the content. But the height should be till bottom, doesn't matter what the screen's size. Thanks.
Any queries are welcome here.
If you can calculate the height of other widgets in the screen above the tabBar then using MediaQuery.of(context).size.height you will get the height of the screen. Deduct the remaining height from the screen height and you can use the resulting value.
P.S. Be careful with the calculations and deduct every height value other than the tab including the safe area one that you will get from MediaQuery.of(context).padding.top & MediaQuery.of(context).padding.bottom.

Make container widget fill parent vertically

TL;DR Need the container to fill the vertical space so that it can act as a ontap listener. Have tried most solutions but nothing seems to work.
So what I am trying to do is to make my container fill up the vertical space while still having a fixed width. Two first is what I have and third is what I want. The idea is to have the container transparent with a gesture ontap listener. If anyone have a better idea as for a different solution, feel free to suggest.
Widget build(BuildContext context) {
return new GestureDetector(
onHorizontalDragUpdate: _move,
onHorizontalDragEnd: _handleDragEnd,
child: new Stack(
children: <Widget>[
new Positioned.fill(
child: new Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
new Container(
child: new IconButton(
padding: new EdgeInsets.only(top: 16.0, bottom: 16.0, left: 24.0, right: 24.0),
icon: new Icon(Icons.warning),
color: Colors.black12,
onPressed: () {},
)
),
],
),
),
new SlideTransition(
position: new Tween<Offset>(
begin: Offset(0.0, 0.0),
end: const Offset(-0.6, 0.0),
).animate(_animation),
child: new Card(
child: new Row(
children: <Widget>[
new Container(
width: 20.0,
height: 20.0,
color: Colors.amber,
),
new Expanded(
child: new Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
_getListTile(),
_ifStoplineIsToBeShown()
],
),
)
],
)
),
),
],
)
);
}
I am quite sure that i have been missing something considering the fact that I have tried a lot of different things and nothing seems to work.
I have also uploaded an image with the debug painting here.
PS. I know I have set the height to a fixed value, but this is the only way to show the container.
The trick is to combine an IntrinsicHeight widget and a Row with crossAxisAlignment: CrossAxisAlignment.stretch
This force the children of Row to expand vertically, but Row will take the least amount of vertical space possible.
Card(
child: IntrinsicHeight(
child: Row(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Container(
width: 20.0,
color: Colors.amber,
),
// Expanded(...)
],
),
)
)
To stretch the container to full height of the parent use property constraints:BoxConstraints.expand() in container widget. Container occupy the complete space independent of the of child widget
Container(
color: Colors.green,
child: Text("Flutter"),
constraints: BoxConstraints.expand(),
)
Please refer the link Container Cheat sheet for more about container
Simply pass in: double.infinity.
If you want a Container to fill all available space, you can just pass in:
width: double.infinity,
height: double.infinity
Explanation:
In Flutter, a child widget cannot exceed the "layout constraints" imposed by its parent widget. During the layout phase, Flutter engine uses a constraint solver to automatically correct "out-of-bound" values into what's allowed by its parent constraints.
For example, if you have a Container that's 50x50, and for its child, you pass in another Container that's 300x300, the inner container will be automatically corrected to "not exceed its parent", thus 50x50. Therefore, using sufficiently large values would always make sure you "fill parent".
In fact, even BoxConstraints.expand() exploits the same idea internally. If you open up the source code of expand(), you will see:
/// Creates box constraints that expand to fill another box constraints.
///
/// If width or height is given, the constraints will require exactly the
/// given value in the given dimension.
const BoxConstraints.expand({
double width,
double height,
}) : minWidth = width ?? double.infinity,
maxWidth = width ?? double.infinity,
minHeight = height ?? double.infinity,
maxHeight = height ?? double.infinity;
So if you are absolutely certain you want to fill all spaces, you can intuitively pass in a number bigger than the parent (or larger than the whole screen), like double.infinity.
As of Jan 2020 the simplest is to use an Expanded Widget
Expanded(flex: 1,
child: Container(..),
),
https://api.flutter.dev/flutter/widgets/Expanded-class.html
There are many answers which suggest using two things
constraints: BoxConstraints.expand(),
height: double.infinity,
But both these answer will give you an error like
BoxConstraints forces an infinite height.
We can avoid these by calculating the height of the screen like
App Bar
Top Bar Space(Exist on the above App Bar)
Remaining screen
1. Get the MediaQuery
final mediaQuery = MediaQuery.of(context);
2. Declare the AppBar Widget and same App Bar instance should be used in Scaffold App Bar
final PreferredSizeWidget appBar = AppBar(
title: Text('Home'),
);
3. Use calculated height
Container(
width: mediaQuery.size.width,
height: (mediaQuery.size.height -
appBar.preferredSize.height -
mediaQuery.padding.top),
color: Colors.red,
),
Output:
Set the height or width of a container to double.maxFinite
Container(
height: double.maxFinite,
width: 100,)
You can make your widget take the full size of a Container widget, and then set the container's height and/or width to double.maxFinite. This will make the Container take the height and/or width or its parent widget
I propose using Expanded widget (which allows us to avoid IntrinsicHeight widget), combine it with the Container's alignment property and therefore make it work properly even if the Container is not the only one at the screen.
Expanded(
child: Container(
alignment: Alignment.center,
child: Text('Your text', textAlign: TextAlign.center))),
That way one also avoids potential app's crash which occurs often when you accidentally expand to infinity some parts of the widget tree both horizontally and vertically (that is why you are not able to use BoxConstraints widget in many cases).
One can read more about the problems of passing constraints in Flutter here - a must read: https://medium.com/flutter-community/flutter-the-advanced-layout-rule-even-beginners-must-know-edc9516d1a2
This work works for me
height: MediaQuery.of(context).size.height,