UI skeleton loading is a technique used to enhance user experience during web or app loading. It involves displaying a simplified, static version of the user interface while the actual content is being fetched. This placeholder UI gives the illusion of instant loading and prevents users from perceiving long loading times.
Creating a skeleton-layout for your screens doesn't only feel like a duplicate work but things can go out of sync real quick, when updating the actual layout we often forget to update the corresponding skeleton-layout.
As the name suggests, skeletonizer will reduce your already existing layouts into mere skeletons and apply painting effects on them, typically a shimmer effect. It automatically does the job for you, in addition skeleton annotations can be used to change how specific widgets are skeletonized.
Simply wrap your layout with Skeletonizer widget or SliverSkeletonizer | Skeletonizer.sliver for sliver widgets.
Skeletonizer(
enabled: _loading,
child: ListView.builder(
itemCount: 7,
itemBuilder: (context, index) {
return Card(
child: ListTile(
title: Text('Item number $index as title'),
subtitle: const Text('Subtitle here'),
trailing: const Icon(Icons.ac_unit),
),
);
},
),
)Note: all the following shimmer effects are disturbed by the gif optimization
Skeletonizer(ignoreContainers: true)
In order for skeletonizer to work it actually needs a layout, but in most cases the layout would
need data to shape, e.g the following ListView ill not render anything unless users is populated, because if users is empty
we have no layout which means we have nothing to skeletonize.
Skeletonizer(
enabled: _loading,
child: ListView.builder(
itemCount: users.lenght,
itemBuilder: (context, index) {
return Card(
child: ListTile(
title: Text(users[index].name),
subtitle: Text(users[index].jobTitle),
leading: CircleAvatar(
radius: 24,
backgroundImage: NetworkImage(users[index].avatar),
),
),
);
},
),
)So the key here is to provide fake data for the layout to shape until the real data is fetched form the server, and we would have such a setup in our build method:
if (_loading) {
final fakeUsers = List.generate(
7, (index) => const User(
name: 'User name',
jobTitle: 'Developer',
avatar: ''
),
);
return Skeletonizer(
child: UserList(users: fakeUsers),
);
} else {
return UserList(users: realUsers);
}
or by utilizing the enabled flag
{
final users = _loading ? List.generate(
7, (index) => const User(
name: 'User name',
jobTitle: 'Developer',
avatar: ''
) : realUsers;
);
return Skeletonizer(
enabled: _loading,
child: UserList(users: users),
);
Now we have our layout but one issue remains, if you run the above example you'll get an error in
your console stating that an invalid url was passed to NetworkImage which is legit because our fake
avatar url is an empty string, in such cases we need to make sure NetworkImage is not in our widget
tree when skeletonizer is enabled and we do that by using a skeleton annotation
called Skeleton.replace ..read more about annotations below.
Skeletonizer(
enabled: _loading,
child: ListView.builder(
itemCount: users.lenght,
itemBuilder: (context, index) {
return Card(
child: ListTile(
title: Text(users[index].name),
subtitle: Text(users[index].jobTitle),
leading: Skeleton.replace(
width: 48, // width of replacement
height: 48, // height of replacement
child; CircleAvatar(
radius: 24,
backgroundImage: NetworkImage(users[index].avatar),
),
),
);
},
),
)or you can do it directly like follows:
Skeletonizer(
enabled: _loading,
child: ListView.builder(
itemCount: users.lenght,
itemBuilder: (context, index) {
return Card(
child: ListTile(
title: Text(users[index].name),
subtitle: Text(users[index].jobTitle),
leading: CircleAvatar(
radius: 24,
backgroundImage: _loading ? null : NetworkImage(users[index].avatar),
),
),
),);
},
),
)Note: you can also check wither a skeletonizer is enabled inside descendent widgets using:
Skeletonizer.of(context).enabled;We can use annotations to change how some widgets should be skeletonized, skeleton annotations have no effect on the real layout as they only hold information for skeletonizer to use when it's enabled.
Widgets annotated with Skeleton.ignore will not be skeletonized
Card(
child: ListTile(
title: Text('The title goes here'),
subtitle: Text('Subtitle here'),
trailing: Skeleton.ignore( // the icon will not be skeletonized
child: Icon(Icons.ac_unit, size: 40),
),
),
)
Ignored multiple descendants demo
Card(
child: Skeleton.ignore( // all descendents will be ignored
child: ListTile(
title: Text('The title goes here'),
subtitle: Text('Subtitle here'),
trailing: Icon(Icons.ac_unit, size: 40),
),
),
)
Widgets annotated with Skeleton.keep will not be skeletonized but will be painted as is
Card(
child: ListTile(
title: Text('The title goes here'),
subtitle: Text('Subtitle here'),
trailing: Skeleton.keep( // the icon will be painted as is
child: Icon(Icons.ac_unit, size: 40),
),
),
)
Widgets annotated with Skeleton.shade will not be skeletonized but will be shaded by a shader mask
Card(
child: ListTile(
title: Text('The title goes here'),
subtitle: Text('Subtitle here'),
trailing: Skeleton.shade( // the icon will be shaded by shader mask
child: Icon(Icons.ac_unit, size: 40),
),
),
)
Widgets annotated with Skeleton.replace will be replaced when skeletonizer is enabled and the
replacement will be skeletonized, This is good for widgets that can not render with fake data
like Image.network()
Card(
child: ListTile(
title: Text('The title goes here'),
subtitle: Text('Subtitle here'),
trailing: Skeleton.replace( // the icon will be replaced when skeletonizer is enabled
width: 50, // the width of the replacement
height: 50, // the height of the replacement
replacment: // defaults to a DecoratedBox
child: Icon(Icons.ac_unit, size: 40),
),
)
,)
Widgets annotated with Skeleton.unite will not be united and drawn as one big bone, this is good
for when you have multiple small bones close to each other and you want to present them as one bone.
Card(
child: ListTile(
title: Text('Item number 1 as title'),
subtitle: Text('Subtitle here'),
trailing: Skeleton.unite(
child: Row(
mainAxisSize: MainAxisSize.min,
children: [
Icon(Icons.ac_unit, size: 32),
SizedBox(width: 8),
Icon(Icons.access_alarm, size: 32),
],
),
),
),
)
,
This annotation can also be used to merge a while layout and present it as one
Skeleton.unite(
child: Card(
child: ListTile(
title: Text('Item number 1 as title'),
subtitle: Text('Subtitle here'),
trailing: Row(
mainAxisSize: MainAxisSize.min,
children: [
Icon(Icons.ac_unit, size: 32),
SizedBox(width: 8),
Icon(Icons.access_alarm, size: 32),
],
),
),
),
)
Skeletonizer has 3 different painting effects to choose from which can be customized to your liking.
Note: Loading effects are disturbed by Gif optimization, these look much better on flutter
You can provide a global text config options to skeletonizer widgets like
Skeletonizer(
justifyMultiLineText: false,
textBoneBorderRadius: TextBoneBorderRadius.fromHeightFactor(.5),
...
)
Use SkeletonizerConfig somewhere up your widgets tree e.g above the MaterialApp widget to
provide
default skeletonizer configurations to your whole App.
SkeletonizerConfig(
data: SkeletonizerConfigData(
effect: const ShimmerEffect(),
justifyMultiLineText: true,
textBorderRadius: TextBoneBorderRadius(..),
ignoreContainers: false,
),
.....
)You can support skeletonizer by liking it on Pub and staring it on Github, sharing ideas on how we can enhance a certain functionality or by reporting any problems you encounter and of course buying a couple coffees will help speed up the development process.