Ekhlass/Flutter_Documentation · Datasets at Hugging Face

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example, the “elastic” curves overshoot briefly in order to represent
a bouncing effect. The interpolation logic typically can extrapolate
past the start or end as appropriate. For some types, for example,
when interpolating colors, the t value is effectively clamped to
the 0.0-1.0 range.
<topic_end>
<topic_start>Understanding constraints
info Note
If you are experiencing specific layout errors,
you might check out Common Flutter errors.When someone learning Flutter asks you why some widget
with width: 100 isn’t 100 pixels wide,
the default answer is to tell them to put that widget
inside of a Center, right?Don’t do that.If you do, they’ll come back again and again,
asking why some FittedBox isn’t working,
why that Column is overflowing, or what
IntrinsicWidth is supposed to be doing.Instead, first tell them that Flutter layout is very different
from HTML layout (which is probably where they’re coming from),
and then make them memorize the following rule:Flutter layout can’t really be understood without knowing
this rule, so Flutter developers should learn it early on.In more detail:For example, if a composed widget contains a column
with some padding, and wants to lay out its two children
as follows:The negotiation goes something like this:Widget: “Hey parent, what are my constraints?”Parent: “You must be from 0 to 300 pixels wide,
and 0 to 85 tall.”Widget: “Hmmm, since I want to have 5 pixels of padding,
then my children can have at most 290 pixels of width
and 75 pixels of height.”Widget: “Hey first child, You must be from 0 to 290
pixels wide, and 0 to 75 tall.”First child: “OK, then I wish to be 290 pixels wide,
and 20 pixels tall.”Widget: “Hmmm, since I want to put my second child below the
first one, this leaves only 55 pixels of height for
my second child.”Widget: “Hey second child, You must be from 0 to 290 wide,
and 0 to 55 tall.”Second child: “OK, I wish to be 140 pixels wide,
and 30 pixels tall.”Widget: “Very well. My first child has position x: 5 and y: 5,
and my second child has x: 80 and y: 25.”Widget: “Hey parent, I’ve decided that my size is going to be 300
pixels wide, and 60 pixels tall.”<topic_end>
<topic_start>Limitations
Flutter’s layout engine is designed to be a one-pass process.
This means that Flutter lays out its widgets very efficiently,
but does result in a few limitations:A widget can decide its own size only within the
constraints given to it by its parent.
This means a widget usually
can’t have any size it wants.A widget can’t know and doesn’t decide its own position
in the screen, since it’s the widget’s parent who decides
the position of the widget.Since the parent’s size and position, in its turn,
also depends on its own parent, it’s impossible to
precisely define the size and position of any widget
without taking into consideration the tree as a whole.If a child wants a different size from its parent and
the parent doesn’t have enough information to align it,
then the child’s size might be ignored.
Be specific when defining alignment.In Flutter, widgets are rendered by their underlying
RenderBox objects. Many boxes in Flutter,
especially those that just take a single child,
pass their constraint on to their children.Generally, there are three kinds of boxes,
in terms of how they handle their constraints:Some widgets, for example Container,
vary from type to type based on their constructor arguments.
The Container constructor defaults
to trying to be as big as possible, but if you give it a width,
for instance, it tries to honor that and be that particular size.Others, for example Row and Column (flex boxes)
vary based on the constraints they are given,
as described in the Flex section.<topic_end>
<topic_start>Examples
For an interactive experience, use the following DartPad.
Use the numbered horizontal scrolling bar to switch between
29 different examples.
<code_start>import 'package:flutter/material.dart';
void main() => runApp(const HomePage());
const red = Colors.red;
const green = Colors.green;
const blue = Colors.blue;
const big = TextStyle(fontSize: 30);
//////////////////////////////////////////////////
class HomePage extends StatelessWidget {
const HomePage({super.key});
@override
Widget build(BuildContext context) {
return const FlutterLayoutArticle([
Example1(),
Example2(),
Example3(),
Example4(),
Example5(),
Example6(),
Example7(),
Example8(),
Example9(),
Example10(),
Example11(),
Example12(),
Example13(),
Example14(),
Example15(),
Example16(),
Example17(),
Example18(),
Example19(),
Example20(),
Example21(),
Example22(),
Example23(),
Example24(),
Example25(),
Example26(),
Example27(),

example, the “elastic” curves overshoot briefly in order to represent

a bouncing effect. The interpolation logic typically can extrapolate

past the start or end as appropriate. For some types, for example,

when interpolating colors, the t value is effectively clamped to

the 0.0-1.0 range.

<topic_end>

<topic_start>Understanding constraints

info Note

If you are experiencing specific layout errors,

you might check out Common Flutter errors.When someone learning Flutter asks you why some widget

with width: 100 isn’t 100 pixels wide,

the default answer is to tell them to put that widget

inside of a Center, right?Don’t do that.If you do, they’ll come back again and again,

asking why some FittedBox isn’t working,

why that Column is overflowing, or what

IntrinsicWidth is supposed to be doing.Instead, first tell them that Flutter layout is very different

from HTML layout (which is probably where they’re coming from),

and then make them memorize the following rule:Flutter layout can’t really be understood without knowing

this rule, so Flutter developers should learn it early on.In more detail:For example, if a composed widget contains a column

with some padding, and wants to lay out its two children

as follows:The negotiation goes something like this:Widget: “Hey parent, what are my constraints?”Parent: “You must be from 0 to 300 pixels wide,

and 0 to 85 tall.”Widget: “Hmmm, since I want to have 5 pixels of padding,

then my children can have at most 290 pixels of width

and 75 pixels of height.”Widget: “Hey first child, You must be from 0 to 290

pixels wide, and 0 to 75 tall.”First child: “OK, then I wish to be 290 pixels wide,

and 20 pixels tall.”Widget: “Hmmm, since I want to put my second child below the

first one, this leaves only 55 pixels of height for

my second child.”Widget: “Hey second child, You must be from 0 to 290 wide,

and 0 to 55 tall.”Second child: “OK, I wish to be 140 pixels wide,

and 30 pixels tall.”Widget: “Very well. My first child has position x: 5 and y: 5,

and my second child has x: 80 and y: 25.”Widget: “Hey parent, I’ve decided that my size is going to be 300

pixels wide, and 60 pixels tall.”<topic_end>

<topic_start>Limitations

Flutter’s layout engine is designed to be a one-pass process.

This means that Flutter lays out its widgets very efficiently,

but does result in a few limitations:A widget can decide its own size only within the

constraints given to it by its parent.

This means a widget usually

can’t have any size it wants.A widget can’t know and doesn’t decide its own position

in the screen, since it’s the widget’s parent who decides

the position of the widget.Since the parent’s size and position, in its turn,

also depends on its own parent, it’s impossible to

precisely define the size and position of any widget

without taking into consideration the tree as a whole.If a child wants a different size from its parent and

the parent doesn’t have enough information to align it,

then the child’s size might be ignored.

Be specific when defining alignment.In Flutter, widgets are rendered by their underlying

RenderBox objects. Many boxes in Flutter,

especially those that just take a single child,

pass their constraint on to their children.Generally, there are three kinds of boxes,

in terms of how they handle their constraints:Some widgets, for example Container,

vary from type to type based on their constructor arguments.

The Container constructor defaults

to trying to be as big as possible, but if you give it a width,

for instance, it tries to honor that and be that particular size.Others, for example Row and Column (flex boxes)

vary based on the constraints they are given,

as described in the Flex section.<topic_end>

<topic_start>Examples

For an interactive experience, use the following DartPad.

Use the numbered horizontal scrolling bar to switch between

29 different examples.

<code_start>import 'package:flutter/material.dart';

void main() => runApp(const HomePage());

const red = Colors.red;

const green = Colors.green;

const blue = Colors.blue;

const big = TextStyle(fontSize: 30);

//////////////////////////////////////////////////

class HomePage extends StatelessWidget {

const HomePage({super.key});

@override

Widget build(BuildContext context) {

return const FlutterLayoutArticle([

Example1(),

Example2(),

Example3(),

Example4(),

Example5(),

Example6(),

Example7(),

Example8(),

Example9(),

Example10(),

Example11(),

Example12(),

Example13(),

Example14(),

Example15(),

Example16(),

Example17(),

Example18(),

Example19(),

Example20(),

Example21(),

Example22(),

Example23(),

Example24(),

Example25(),

Example26(),

Example27(),