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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 child
Align—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.
multichild
column, 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.