Position widget in stack with percent - dart

Let's say I want to position a widget inside a Stack but with a percent of the Stack position instead of a fixed size. How to do that in flutter ?
I'd expect that the Positionned.fromRelativeRect constructor would be the thing, using floats between 0 and 1. But seems like no.
Align allows to position the widget in percent. But heightFactor and widthFactor changes the Align size instead of the child size. Which is not what I want.

You can combine a Positioned.fill and LayoutBuilder to achieve such result.
new Stack(
children: <Widget>[
new Positioned.fill(
child: new LayoutBuilder(
builder: (context, constraints) {
return new Padding(
padding: new EdgeInsets.only(top: constraints.biggest.height * .59, bottom: constraints.biggest.height * .31),
child: new Text("toto", textAlign: TextAlign.center,),
);
},
),
)
],
),

one thing that i figured out not long ago is that you can position a widget on the screen using a container its alignment parameter with the help of the Alignment.lerp(x,y,z) function
//the widget will be placed in the center of the container
alignment: Alignment.lerp(Alignment.topCenter, Alignment.bottomCenter, 0),
//the widget will be placed in the bottom of the container
alignment: Alignment.lerp(Alignment.topCenter, Alignment.bottomCenter, 1),
//the widget will be placed in the bottom quarter of the container
alignment: Alignment.lerp(Alignment.topCenter, Alignment.bottomCenter, 0.5),
//the widget will be placed in the top quarter of the container
alignment: Alignment.lerp(Alignment.topCenter, Alignment.bottomCenter, -0.5),

use FractionalOffset & FractionallySizedBox it's very simple in contrast
around no unnecessary code like Positioned.fill
no no extra calculations like Alignment
...
Container(
color: Colors.blue[200],
alignment: FractionalOffset(0.7, 0.6),
child: FractionallySizedBox(
widthFactor: 0.1,
heightFactor: 1/3,
child: Container(color: Colors.red[900])
),
),
...

If you want to use LayoutBuilder then do without Positioned.fill, like this:
you need one LayoutBuilder, no need to turn around every elements and use Transform.translate instead of Padding.
new LayoutBuilder(
builder: (context, constraints) {
return Stack(
children: <Widget>[
Transform.translate(
offset: Offset(
constraints.biggest.width * left,
constraints.biggest.height * top),
child: new Text("toto", textAlign: TextAlign.center,),
),
...
],
);
}
)

Related

Laying out widgets from the corners and grow one with window

I’d like to place
an unspecified number of Text widgets from top-left to bottom
3 TextButton widgets from bottom-right to left and
a random parent content widget top-right
The Text and TextButton widgets should only take their minimum space while the the content widget should expand to bottom-left (upon windows resizing) with its children centered like so.
Maybe I’m just unlucky or misled/spoiled by Qt’s QSpacerItem…?
This is a desktop App so “windows resizing” really makes sense in flutter context! ;)
Also, more generally, is there a way to directly nest (some kind of) Row/Column instances and stretch Widgets down/right?
You'll want to use a combination of Row, Column and Expanded to achieve this effect.
I'm going to assume that the bottom left corner belongs to the left-hand side bar. With that in mind, your basic structure can look something like this:
Row(
children: [
// Side bar
SizedBox(
width: 250,
ListView.builder(
// Display text widgets
),
),
// This widget will fill whatever space remains in the Row after the side bar
Expanded(
child: Column(
children: [
// This widget will fill all the space before the footer
const Expanded(
child: Center(
child: Text("Resizable Window"),
),
),
// Footer with buttons
SizedBox(
height: 100,
child: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: [
// Your buttons
]
),
),
],
),
),
],
)
Full example on DartPad

Is there a more optimal way to space widgets within a column?

So i'm emulating an old app I have where the UI looks like this
Currently i'm focused on creating the UI layout for the purple side bar, I did that by creating a Container with a purple background. Within the container I created a column with multiple children and just used an empty SizedBox to create distance between one widget from another.
import 'package:flutter/material.dart';
class SignInPage extends StatelessWidget {
const SignInPage({super.key});
#override
Widget build(BuildContext context) {
return Scaffold(
// appBar: AppBar(
// title: Text('Sample Text'),
// elevation: 5.0,
// ),
body: _buildContent(),
);
}
Widget _buildContent() {
// private method
return Container(
color: Colors.deepPurpleAccent,
padding: EdgeInsets.all(16.0),
child: Column(
// crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Container(
color: Colors.orange,
child: SizedBox(
height: 100.0,
width: 80.0,
),
),
SizedBox(
height: 140.0,
),
Container(
color: Colors.red,
child: SizedBox(
height: 50.0,
width: 80.0,
),
),
SizedBox(
height: 8.0,
),
Container(
color: Colors.purple,
child: SizedBox(
height: 50.0,
width: 80.0,
),
),
],
),
);
}
}
I'm quite new to flutter so i'm wondering if there's a better way to structure my layout of the side bar? Also to think in the future, since the name "BagTrack" Is on the same level as "Analytic Overview" Should that just be one giant row"?
Actual answer
Method 1
#Mahfuzur Rahman answer is good, but to actually answer your question about other ways. Flex widgets (Column and Row extend the Flex widget), have both mainAxisAlignment and crossAxisAlignment, they can be used to align them more easily between different devices/screens sizes.
So maybe grouping your red and purple boxes in a Column with mainAxisSize set to MainAxisSize.min, and aligning the surrounding column with a specific size.
https://api.flutter.dev/flutter/widgets/Column-class.html
Method 2
Another way, if you would like some widget to occupy some percentage amount of space from it's parent, I suggest you look into Expanded widget, Flexible widget.
Method 3
Or even FractionallySizedBox could be a good widget for you, but then I would also look at this LayoutBuilder widget to solve the potential Unbounded Height/Width exception.
Second smaller question
It's entirely up to you to decide about your second question concerning the giant row. I wouldn't do it though. Probably would use a const SizedBox or const EdgeInsets (for Padding) and keep them at the same height this way.
Just complementing Flutter knowledge
PS: Since you are new to Flutter. As a suggestion for future performance: avoid the Container widget as much as you know, there are a lot of simpler widgets like SizedBox, ColoredBox, DecoratedBox and Padding that you can use in its place that could be marked as const sometimes and be less expensive.
For understanding final and const:
final is a variable that cannot be reassigned by accident inside your code. When you instantiate it you give it a value and that's it. (Using late changes that a bit but not much);
const is a variable assigned by the compiler, if you are familiar with C it's like #define but there is a little difference, every time you say const EdgeInsets.all(8) for example, the compiler will detect that and use the same variable, so you don't have to remember a specific constant variable name.
Yes there is. But using SizedBox also wont hurt.
I usually Prefer ListTile for each element in the drawer.
ListTile(
leading: GestureDetector(
behavior: HitTestBehavior.translucent,
onTap: () {},
child: Container(
width: 48,
height: 48,
padding: const EdgeInsets.symmetric(vertical: 4.0),
alignment: Alignment.center,
child: const CircleAvatar(),
),
),
title: const Text('title'),
dense: false,
)

Flutter PageView.builder with animated Children sizes

I'm trying to recreate this:
I've tried with a PageView.builder, and got this far (sorry for the ugliness of colors but it's for visualization purposes):
This is the Code:
Container(
height: 40 * 2 + 100.0,
child: PageView.builder(
scrollDirection: Axis.horizontal,
controller: controller,
itemCount: 9,
itemBuilder: (context, index) {
double value = 1.0;
try {
value = controller.hasClients
? controller.page - index
: 1.0;
} catch (e) {
value = 1.0;
}
value = value.abs().clamp(0.0, 1.0);
value = 1 - value;
return Padding(
padding: EdgeInsets.symmetric(horizontal: 6.0),
child: Container(
width: value == 1.0 ? 80.0 : 60.0,
height: 30.0,
color: Color.lerp(Colors.green,
Colors.red, value),
child: Center(
child: Text(
index.toString(),
style: TextStyle(
color: Color.lerp(
Colors.red, Colors.black, value),
fontSize: lerpDouble(20.0, 40.0, value)),
)),
),
);
},
))
And the controller variable is this:
controller = new PageController(initialPage: 5, viewportFraction: 1/4);
controller.addListener(() {
setState(() {});
As you can see I managed to change the color and textSize to the "selected" item (the red ones), but even If I try to set its size to be bigger, it has no effects. I tried with a ListView.builder which made me set different sizes but with it I didn't have page Snapping and a default initial Page, so I opted out.
hope everything is clear.
Is it possible to do it, and if it is, how Could I do it?
I know its an old question but you can change width and height by changing margin of the container. You have to basically change a container (this one inside the Padding widget) margins values by value of your "value" variable and also I would highly suggest using AnimatedContainer for out of the box animations. Add this code to your container:
EdgeInsets.only(bottom: 50, right: value == 1.0? 20 : 40, left: value == 1.0? 20 : 40, top: value == 1.0? 150 : 250),
You should also remove this code from the container:
width: value == 1.0 ? 80.0 : 60.0,
height: 30.0,

After flutter Upgrade Listtile leading content does not match parent anymore

After doing flutter upgrade yesterday the content of ListTile leading (especially the height) does not match parent anymore.
I have a overflow in height now. Width is working as expected.
As you can see in the picture there is still space below the leading widget.
Does anyone know how to fix this?
Or is there a way to downgrade the flutter version?
Widget _listTile(){
return ListTile(
contentPadding: EdgeInsets.fromLTRB(3.0, 1.0, 0.0, 1.0),
dense: true,
leading: Column(
children: <Widget>[
_leadingButton(),
_leadingProgress
],
),
title: _textSubtitle(subtitle),
subtitle: _textSubtitle(subtitle),
);
}
I believe the change that has caused this is [this one][1]: https://github.com/flutter/flutter/commit/0e2eeb5a485aaccdab7007ad9b90fd8120e77983#diff-53f33273ae4e7462729c5f4b7394428b. If you read the code, it says it was doing an update to adhere to the material spec which means a constraint on the size of the widget, so there's a very good chance it won't change back to how it was. How you were using it was technically against the material spec.
But rather than trying to downgrade flutter, you could simply create your own widget that does the same thing - you don't need to use a ListTile.
Something like this would probably do:
class MyListTile extends StatelessWidget {
final Widget leading;
final Widget title;
final Widget subtitle;
final EdgeInsets padding;
MyListTile({#required this.leading, #required this.title, #required this.subtitle, this.padding});
#override
void build(BuildContext context) {
return Padding(
padding: padding ?? EdgeInsets.zero,
child: Row(
children: [
leading,
Expanded(
child: Column(
mainAxisSize: MainAxisSize.min,
children: [
title,
subtitle,
],
),
),
],
),
);
}
}
Full disclosure though - I haven't run that code or even put it in an IDE so it may have issues, but that should illustrate the basics of what you're trying to do there. You'd probably want to wrap things in padding (most likely at least the leading widget) as needed to get the spacing you currently have.

Flutter: Constraints not constraining widget (explanation needed)

class Test extends StatelessWidget {
Widget build(BuildContext context) {
return UnconstrainedBox(
child: Container(
height: 250.0,
width: 250.0,
decoration:
BoxDecoration(shape: BoxShape.circle, color: Colors.red),
child: Opacity(
opacity: 0.5,
child: Container( // WIDGET IN QUESTION
constraints:
BoxConstraints.expand(width: 50.0, height: 50.0),
color: Colors.yellow))));
}
}
According to the Container class documentation...
If the widget has no child and no alignment, but a height, width, or constraints are provided, then the Container tries to be as small as possible given the combination of those constraints and the parent's constraints.
Instead, the widget is trying to be as large as possible (size of parent) rather than 50x50. I understand that I can use something like UnconstrainedBox, but I'm looking for an explanation of this behavior.
Looking for:
Currently getting:
The problem is your root Container.
By setting a width+height without an alignment, Container forces its child to fill the available space.
If you want that child take the least amount of space, you need to specify your root container how it should align its child within its bounds.
Container(
width: 250,
height: 250,
alignment: Alignment.center,
child: Whatever(),
);

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