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for more information, see the docs on releasing
iOS and android apps.
<topic_end>
<topic_start>
profile
in profile mode, some debugging ability is maintained—enough
to profile your app’s performance. profile mode is disabled on
the emulator and simulator, because their behavior is not representative
of real performance. on mobile, profile mode is similar to release mode,
with the following differences:
profile mode for a web app means that:
your IDE supports this mode. android studio, for example,
provides a run > profile… menu option.
the command flutter run --profile compiles to profile mode.
info note
use the DevTools suite to profile your app’s performance.
for more information on the build modes, see
flutter’s build modes.
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<topic_start>
common flutter errors
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<topic_start>
introduction
this page explains several frequently-encountered flutter
framework errors (including layout errors) and gives suggestions
on how to resolve them.
this is a living document with more errors to be added in
future revisions, and your contributions are welcomed.
feel free to open an issue or submit a pull request to
make this page more useful to you and the flutter community.
<topic_end>
<topic_start>
‘a RenderFlex overflowed…’
RenderFlex overflow is one of the most frequently
encountered flutter framework errors,
and you’ve probably run into it already.
what does the error look like?
when it happens, yellow and black stripes appear,
indicating the area of overflow in the app UI.
in addition, an error message displays in the debug console:
how might you run into this error?
the error often occurs when a column or row has a
child widget that isn’t constrained in its size.
for example,
the code snippet below demonstrates a common scenario:
<code_start>
widget build(BuildContext context) {
return row(
children: [
const Icon(Icons.message),
column(
mainAxisSize: MainAxisSize.min,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text('Title', style: Theme.of(context).textTheme.headlineMedium),
const text(
'lorem ipsum dolor sit amet, consectetur adipiscing elit, sed '
'do eiusmod tempor incididunt ut labore et dolore magna '
'aliqua. ut enim ad minim veniam, quis nostrud '
'exercitation ullamco laboris nisi ut aliquip ex ea '
'commodo consequat.',
),
],
),
],
);
}
<code_end>
in the above example,
the column tries to be wider than the space the row
(its parent) can allocate to it, causing an overflow error.
why does the column try to do that?
to understand this layout behavior, you need to know
how flutter framework performs layout:
“to perform layout, flutter walks the render tree in a depth-first traversal
and passes down size constraints from parent to child… children respond by
passing up a size to their parent object within the constraints the parent
established.” – flutter architectural overview
in this case, the row widget doesn’t constrain the
size of its children, nor does the column widget.
lacking constraints from its parent widget, the second
text widget tries to be as wide as all the characters
it needs to display. the self-determined width of the
text widget then gets adopted by the column, which
clashes with the maximum amount of horizontal space its parent,
the row widget, can provide.
how to fix it?
well, you need to make sure the column won’t attempt
to be wider than it can be. to achieve this,
you need to constrain its width. one way to do it is to
wrap the column in an expanded widget:
<code_start>
return const row(
children: [
Icon(Icons.message),
expanded(
child: column(
// code omitted
),