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---

- [Introduction](#introduction)
- [Basic usage](#basic-usage)
- [The need for fake data](#the-need-for-fake-data)
- [Annotations](#annotations)
- [Creating Skeletons manually](#creating-skeletons-manually)
- [Customization](#customization)
- [Resources](#resources)

## Introduction

### What are skeleton loaders?

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.

### Motivation

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.

### How does it work?

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.

## Basic usage

Simply wrap your layout with `Skeletonizer` widget or `SliverSkeletonizer` | `Skeletonizer.sliver` for sliver widgets.

```dart

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),
        ),
      );
    },
  ),
)
```



#### Skeletonizer with default config
**Note: all the following shimmer effects are disturbed by the gif optimization**

[Click here for HD video demo](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/skeletonizer_demo_video.mp4?raw=true)

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/skeletonizer_demo_1.gif?raw=true)

#### Skeletonizer with no containers

```dart

Skeletonizer(ignoreContainers: true)
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/skeletonizer_demo_2.gif?raw=true)

## The need for fake data

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 will not render anything unless `users` is populated, because if users is empty
we have no layout which means we have nothing to skeletonize.

```dart
Skeletonizer(
  enabled: _loading,
  child: ListView.builder(
    itemCount: users.length,
    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:

```dart
 
  if (_loading) {
    final fakeUsers = List.filled(7, User(
        name: 'User name',
        jobTitle: 'Developer',
        avatar: ''
      ),
    );
    return Skeletonizer(
      child: UserList(users: fakeUsers),
    );
  } else {
    return UserList(users: realUsers);
  }  

```



or by utilizing the `enabled` flag

```dart
  {
  final users = _loading ? List.filled(
      7, const User(
      name: 'User name',
      jobTitle: 'Developer',
      avatar: ''
  ) : realUsers;
  );
  return Skeletonizer(
    enabled: _loading,
    child: UserList(users: users),
  );
 
```
**Note**: you can use BoneMock to easily generate fake text for your mock data

```dart
 
 
    final fakeUsers = List.filled(7, User(
        name: BoneMock.name,
        jobTitle: BoneMock.words(2),
        email: BoneMock.email,
        createdAt: BoneMock.date, 
      ),
    );
     

```


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.

```dart
Skeletonizer(
  enabled: _loading,
  child: ListView.builder(
    itemCount: users.length,
    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:

```dart
Skeletonizer(
  enabled: _loading,
  child: ListView.builder(
    itemCount: users.length,
    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:

```dart
Skeletonizer.of(context).enabled;
```

## Annotations

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.

### Skeleton.ignore

Widgets annotated with `Skeleton.ignore` will not be skeletonized

```dart
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),
    ),
  ),
)
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/ignored_skeleton_demo.gif?raw=true)

### Skeleton.leaf
Widgets annotated with `Skeleton.leaf` marks containers as leafs, leafs are painted using the shader paint.

```dart
Skeleton.leaf(
   child : Card(
    child: ListTile(
        title: Text('The title goes here'),
        subtitle: Text('Subtitle here'),
        trailing: Icon(Icons.ac_unit, size: 40),
      ),
  )
)
```
![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/leaf_skeleton_demo.gif?raw=true)


### Skeleton.keep

Widgets annotated with `Skeleton.keep` will not be skeletonized but will be painted as is

```dart
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),
    ),
  ),
)
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/kept_skeleton_demo.gif?raw=true)

### Skeleton.shade

Widgets annotated with `Skeleton.shade` will not be skeletonized but will be shaded by a shader mask.

**Note**: `CustomPainter` widgets need to be explicitly annotated with `Skeleton.shade` to be shaded.

```dart
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),
    ),
  ),
)
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/shaded_skeleton_demo.gif?raw=true)

### Skeleton.replace

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()`

```dart
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
        replacement: // defaults to a DecoratedBox
        child: Icon(Icons.ac_unit, size: 40),
  ),
)
,)
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/replaced_skeleton_demo.gif?raw=true)

### Skeleton.unite
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.

```dart
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),
        ],
      ),
    ),
  ),
)
,
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/united_skeleton_demo.gif?raw=true)

### Skeleton.ignorePointers
Widgets annotated with `Skeleton.ignorePointers` will ignore pointer events when skeletonizer is enabled.

## Creating Skeletons manually

Originally, Skeletonizer worked its magic by creating skeletons from real widgets. But hey, we get it – sometimes you want to do your own thing, have a different layout, or just skip the whole fake data scene. Now, you can speed things up big time by crafting custom skeletons from scratch using Bone widgets. Now, you might wonder, "What sets this apart from other shimmer libraries?" Simple – Bone widgets are your time-saving superheroes. They mimic everyday UI components you'd typically want to shimmer, such as icons, texts, and buttons and use their actual theme data to design border radius and sizing information.
```dart
Skeletonizer.zone(
    child: Card(
      child: ListTile(
        leading: Bone.circle(size: 48),  
        title: Bone.text(words: 2),
        subtitle: Bone.text(),
        trailing: Bone.icon(), 
      ),
    ),
 );
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/bone_widgets_demo.png?raw=true)

Obviously, you can create any bone shape using `Bone(width, height)` or use the helpers `Bone.circle(size)` and `Bone.square(size)`. The cool part here is using mimic bone types like `Bone.icon()`, which, you guessed it, reads icon sizing information from the inherited theme. As such, Bone.text reads font size and line height from the inherited theme if not provided in the constructor. By default, it mimics 3 words (word = 5 letters), but you can easily change that. For multiline, use `Bone.multiText(lines: 3)`.

Additionally, there's also `Bone.button()` which mimics actual Material buttons and `Bone.iconButton()` to mimic icon buttons.

When opting for the manual approach, only Bone widgets get the shimmer treatment – they're the ones that'll be shaded. This means you can wrap other colorable widgets like cards, containers ..etc, without worrying about them getting shaded. which results to a seamless and perfect shimmer effect!
## Customization

### Loading effects

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**

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/loading_effects_demo.gif?raw=true)

Effects are configurable, e.g you can change the base color, highlight color, direction, and duration of ShineEffect like so:

```dart
Skeletonizer(
  effect: const ShimmerEffect(
    baseColor: Colors.grey[300],
    highlightColor: Colors.grey[100],
    duration: Duration(seconds: 1),
  ),
  child: ...
)
```

### Animating the transition between skeleton and content (Slivers are not supported)
 you can animate the transition between skeleton and content by setting `enableSwitchAnimation` to true, animation can be customized by providing a `SwitchAnimationConfig`.

```dart
SwitchAnimationConfig({
    this.duration = const Duration(milliseconds: 300),
    this.switchInCurve = Curves.linear,
    this.switchOutCurve = Curves.linear,
    this.transitionBuilder = AnimatedSwitcher.defaultTransitionBuilder,
    this.layoutBuilder = AnimatedSwitcher.defaultLayoutBuilder,
    this.reverseDuration,
}); 
```

### Text skeleton config

You can provide a global text config options to skeletonizer widgets like

```dart
Skeletonizer(
    justifyMultiLineText: false,
    textBoneBorderRadius: TextBoneBorderRadius.fromHeightFactor(.5),
    ...
)
```

![](https://github.com/Milad-Akarie/skeletonizer/blob/main/art/text_config_demo.gif?raw=true)

### ignoreContainers
if you want to ignore all containers and only skeletonize their children you can set
`ignoreContainers` to true

### containersColor
if provided, all containers will be painted with this color otherwise the actual color will be

### Using the inheritable Config data
You can pass a `SkeletonizerConfigData` as a theme extension to provide default configurations to
all skeletonizer widgets in your app.

```dart
MaterialApp(
  theme: ThemeData(
    extensions: const [
      SkeletonizerConfigData(), // default constructor has light theme config
    ],
  ),
  darkTheme: ThemeData(
    brightness: Brightness.dark,
    extensions: const [
      SkeletonizerConfigData.dark(), // dark theme config
    ],
  ),
  ...
)
```
or you can Use `SkeletonizerConfig` to provide inheritable config data to all descendant Skeletonizer widgets.

```dart
SkeletonizerConfig(
    data: SkeletonizerConfigData(
      effect: const ShimmerEffect(),
      justifyMultiLineText: true,
      textBorderRadius: TextBoneBorderRadius(..),
      ignoreContainers: false,
    ),
    .....
)
```
## Resources
- [Flutter skeleton loader using skeletonizer](https://medium.com/@milad-akarie/flutter-skeleton-loader-using-skeletonizer-13d410dc4ac7)

### Support Skeletonizer

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.
