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<topic_end>
<topic_start>
hot reload
flutter’s hot reload feature helps you quickly and
easily experiment, build UIs, add features, and fix bugs.
hot reload works by injecting updated source code files
into the running dart virtual machine (vm).
after the VM updates classes with the new versions of fields and functions,
the flutter framework automatically rebuilds the widget tree,
allowing you to quickly view the effects of your changes.
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<topic_start>
how to perform a hot reload
to hot reload a flutter app:
if you’re working in an IDE/editor that supports flutter’s IDE tools,
select save all (cmd-s/ctrl-s),
or click the hot reload button on the toolbar.
if you’re running the app at the command line using flutter run,
enter r in the terminal window.
after a successful hot reload operation,
you’ll see a message in the console similar to:
the app updates to reflect your change,
and the current state of the app is preserved.
your app continues to execute from where it was prior
to run the hot reload command.
the code updates and execution continues.
what is the difference between hot reload, hot restart,
and full restart?
flutter web currently supports hot restart but not
hot reload.
controls for run, run debug, hot reload, and hot restart in android studio
a code change has a visible effect only if the modified
dart code is run again after the change. specifically,
a hot reload causes all the existing widgets to rebuild.
only code involved in the rebuilding of the widgets
is automatically re-executed. the main() and initState()
functions, for example, are not run again.
<topic_end>
<topic_start>
special cases
the next sections describe specific scenarios that involve
hot reload. in some cases, small changes to the dart code
enable you to continue using hot reload for your app.
in other cases, a hot restart, or a full restart is needed.
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<topic_start>
an app is killed
hot reload can break when the app is killed.
for example, if the app was in the background for too long.
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<topic_start>
compilation errors
when a code change introduces a compilation error,
hot reload generates an error message similar to:
in this situation, simply correct the errors on the
specified lines of dart code to keep using hot reload.
<topic_end>
<topic_start>
CupertinoTabView’s builder
hot reload won’t apply changes made to
a builder of a CupertinoTabView.
for more information, see issue 43574.
<topic_end>
<topic_start>
enumerated types
hot reload doesn’t work when enumerated types are
changed to regular classes or regular classes are
changed to enumerated types.
for example:
before the change:
<code_start>
enum color {
red,
green,
blue,
}
<code_end>
after the change:
<code_start>
class color {
color(this.i, this.j);
final int i;
final int j;
}
<code_end>
<topic_end>
<topic_start>
generic types
hot reload won’t work when generic type declarations
are modified. for example, the following won’t work:
before the change:
<code_start>
class A<T> {
t? i;
}
<code_end>
after the change:
<code_start>
class A<T, v> {
t? i;