Ekhlass/Flutter_Documentation · Datasets at Hugging Face

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<topic_start>Building adaptive apps
<topic_end>
<topic_start>
Overview
Flutter provides new opportunities to build apps that can
run on mobile, desktop, and the web from a single codebase.
However, with these opportunities, come new challenges.
You want your app to feel familiar to users,
adapting to each platform by maximizing usability and
ensuring a comfortable and seamless experience.
That is, you need to build apps that are not just
multiplatform, but are fully platform adaptive.There are many considerations for developing platform-adaptive
apps, but they fall into three major categories:This page covers all three categories in detail
using code snippets to illustrate the concepts.
If you’d like to see how these concepts come together,
check out the Flokk and Folio examples that
were built using the concepts described here.Original demo code for adaptive app development techniques from flutter-adaptive-demo.<topic_end>
<topic_start>
Building adaptive layouts
One of the first things you must consider when writing
your app for multiple platforms is how to adapt
it to the various sizes and shapes of the screens that
it will run on.<topic_end>
<topic_start>
Layout widgets
If you’ve been building apps or websites,
you’re probably familiar with creating responsive interfaces.
Luckily for Flutter developers,
there are a large set of widgets to make this easier.Some of Flutter’s most useful layout widgets include:Single childAlign—Aligns a child within itself.
It takes a double value between -1 and 1,
for both the vertical and horizontal alignment.AspectRatio—Attempts to size the
child to a specific aspect ratio.ConstrainedBox—Imposes size constraints on its child,
offering control over the minimum or maximum size.CustomSingleChildLayout—Uses a delegate function
to position a single child. The delegate can determine
the layout constraints and positioning for the child.Expanded and Flexible—Allows a child of a
Row or Column to shrink or grow to fill any available space.FractionallySizedBox—Sizes its child to a fraction
of the available space.LayoutBuilder—Builds a widget that can reflow
itself based on its parents size.SingleChildScrollView—Adds scrolling to a single child.
Often used with a Row or Column.MultichildColumn, Row, and Flex—Lays out children
in a single horizontal or vertical run.
Both Column and Row extend the Flex widget.CustomMultiChildLayout—Uses a delegate function to
position multiple children during the layout phase.Flow—Similar to CustomMultiChildLayout,
but more efficient because it’s performed during the
paint phase rather than the layout phase.ListView, GridView, and
CustomScrollView—Provides scrollable
lists of children.Stack—Layers and positions multiple children
relative to the edges of the Stack.
Functions similarly to position-fixed in CSS.Table—Uses a classic table layout algorithm for
its children, combining multiple rows and columns.Wrap—Displays its children in multiple horizontal
or vertical runs.To see more available widgets and example code, see
Layout widgets.<topic_end>
<topic_start>
Visual density
Different input devices offer various levels of precision,
which necessitate differently sized hit areas.
Flutter’s VisualDensity class makes it easy to adjust the
density of your views across the entire application,
for example, by making a button larger
(and therefore easier to tap) on a touch device.When you change the VisualDensity for your MaterialApp,
MaterialComponents that support it animate their densities
to match. By default, both horizontal and vertical densities
are set to 0.0, but you can set the densities to any negative
or positive value that you want. By switching between different
densities, you can easily adjust your UI:To set a custom visual density, inject the density into
your MaterialApp theme:
<code_start>double densityAmt = touchMode ? 0.0 : -1.0;
VisualDensity density =
VisualDensity(horizontal: densityAmt, vertical: densityAmt);
return MaterialApp(
theme: ThemeData(visualDensity: density),
home: MainAppScaffold(),
debugShowCheckedModeBanner: false,
);<code_end>
To use VisualDensity inside your own views,
you can look it up:
<code_start>VisualDensity density = Theme.of(context).visualDensity;<code_end>
Not only does the container react automatically to changes
in density, it also animates when it changes.
This ties together your custom components,
along with the built-in components,
for a smooth transition effect across the app.As shown, VisualDensity is unit-less,
so it can mean different things to different views.
In this example, 1 density unit equals 6 pixels,
but this is totally up to your views to decide.
The fact that it is unit-less makes it quite versatile,
and it should work in most contexts.It’s worth noting that the Material Components generally
use a value of around 4 logical pixels for each
visual density unit. For more information about the
supported components, see VisualDensity API.
For more information about density principles in general,
see the Material Design guide.<topic_end>
<topic_start>
Contextual layout
If you need more than density changes and can’t find a
widget that does what you need, you can take a more
procedural approach to adjust parameters, calculate sizes,
swap widgets, or completely restructure your UI to suit
a particular form factor.<topic_end>
<topic_start>Screen-based breakpoints
The simplest form of procedural layouts uses

<topic_start>Building adaptive apps

<topic_end>

<topic_start>

Overview

Flutter provides new opportunities to build apps that can

run on mobile, desktop, and the web from a single codebase.

However, with these opportunities, come new challenges.

You want your app to feel familiar to users,

adapting to each platform by maximizing usability and

ensuring a comfortable and seamless experience.

That is, you need to build apps that are not just

multiplatform, but are fully platform adaptive.There are many considerations for developing platform-adaptive

apps, but they fall into three major categories:This page covers all three categories in detail

using code snippets to illustrate the concepts.

If you’d like to see how these concepts come together,

check out the Flokk and Folio examples that

were built using the concepts described here.Original demo code for adaptive app development techniques from flutter-adaptive-demo.<topic_end>

<topic_start>

Building adaptive layouts

One of the first things you must consider when writing

your app for multiple platforms is how to adapt

it to the various sizes and shapes of the screens that

it will run on.<topic_end>

<topic_start>

Layout widgets

If you’ve been building apps or websites,

you’re probably familiar with creating responsive interfaces.

Luckily for Flutter developers,

there are a large set of widgets to make this easier.Some of Flutter’s most useful layout widgets include:Single childAlign—Aligns a child within itself.

It takes a double value between -1 and 1,

for both the vertical and horizontal alignment.AspectRatio—Attempts to size the

child to a specific aspect ratio.ConstrainedBox—Imposes size constraints on its child,

offering control over the minimum or maximum size.CustomSingleChildLayout—Uses a delegate function

to position a single child. The delegate can determine

the layout constraints and positioning for the child.Expanded and Flexible—Allows a child of a

Row or Column to shrink or grow to fill any available space.FractionallySizedBox—Sizes its child to a fraction

of the available space.LayoutBuilder—Builds a widget that can reflow

itself based on its parents size.SingleChildScrollView—Adds scrolling to a single child.

Often used with a Row or Column.MultichildColumn, Row, and Flex—Lays out children

in a single horizontal or vertical run.

Both Column and Row extend the Flex widget.CustomMultiChildLayout—Uses a delegate function to

position multiple children during the layout phase.Flow—Similar to CustomMultiChildLayout,

but more efficient because it’s performed during the

paint phase rather than the layout phase.ListView, GridView, and

CustomScrollView—Provides scrollable

lists of children.Stack—Layers and positions multiple children

relative to the edges of the Stack.

Functions similarly to position-fixed in CSS.Table—Uses a classic table layout algorithm for

its children, combining multiple rows and columns.Wrap—Displays its children in multiple horizontal

or vertical runs.To see more available widgets and example code, see

Layout widgets.<topic_end>

<topic_start>

Visual density

Different input devices offer various levels of precision,

which necessitate differently sized hit areas.

Flutter’s VisualDensity class makes it easy to adjust the

density of your views across the entire application,

for example, by making a button larger

(and therefore easier to tap) on a touch device.When you change the VisualDensity for your MaterialApp,

MaterialComponents that support it animate their densities

to match. By default, both horizontal and vertical densities

are set to 0.0, but you can set the densities to any negative

or positive value that you want. By switching between different

densities, you can easily adjust your UI:To set a custom visual density, inject the density into

your MaterialApp theme:

<code_start>double densityAmt = touchMode ? 0.0 : -1.0;

VisualDensity density =

VisualDensity(horizontal: densityAmt, vertical: densityAmt);

return MaterialApp(

theme: ThemeData(visualDensity: density),

home: MainAppScaffold(),

debugShowCheckedModeBanner: false,

);<code_end>

To use VisualDensity inside your own views,

you can look it up:

<code_start>VisualDensity density = Theme.of(context).visualDensity;<code_end>

Not only does the container react automatically to changes

in density, it also animates when it changes.

This ties together your custom components,

along with the built-in components,

for a smooth transition effect across the app.As shown, VisualDensity is unit-less,

so it can mean different things to different views.

In this example, 1 density unit equals 6 pixels,

but this is totally up to your views to decide.

The fact that it is unit-less makes it quite versatile,

and it should work in most contexts.It’s worth noting that the Material Components generally

use a value of around 4 logical pixels for each

visual density unit. For more information about the

supported components, see VisualDensity API.

For more information about density principles in general,

see the Material Design guide.<topic_end>

<topic_start>

Contextual layout

If you need more than density changes and can’t find a

widget that does what you need, you can take a more

procedural approach to adjust parameters, calculate sizes,

swap widgets, or completely restructure your UI to suit

a particular form factor.<topic_end>

<topic_start>Screen-based breakpoints

The simplest form of procedural layouts uses