This change reworks how users define previews in their code, expands the
number of valid 'functions' that can be used to create previews, and
allows for specifying a 'wrapper' function to wrap the previewed widget
with
The `WidgetPreview` class has been removed from the framework, with its
properties being added to the `Preview` annotation class instead to
remove some boilerplate from the preview declaration workflow.
Before:
```dart
@Preview()
List<WidgetPreview> previews() => <WidgetPreview>[
WidgetPreview(
name: 'Top-level preview',
child: Text('Foo'),
),
];
```
After:
```dart
@Preview(name: 'Top-level preview')
Widget previews() => Text('Foo');
```
Previews can now be defined using top-level functions, constructors and
factories which take no arguments, and static methods within classes:
Examples:
```dart
@Preview(name: 'Top-level preview')
Widget previews() => Text('Foo');
class MyWidget extends StatelessWidget {
@Preview(name: 'Constructor preview')
MyWidget.preview();
@Preview(name: 'Factory preview')
factory MyWidget.factoryPreview() => MyWidget.preview();
@Preview(name: 'Static preview')
static Widget previewStatic() => Text('Static');
@override
Widget build(BuildContext context) {
return Text('MyWidget');
}
}
```
Users can also provide a `wrapper` function with the signature `Widget
Function(Widget)` to easily wrap previewed widget with shared
bootstrapping logic.
Example:
```dart
Widget testWrapper(Widget child) {
return Provider<int>.value(
value: 42,
child: child,
);
}
@Preview(name: 'Preview with wrapper', wrapper: testWrapper)
Widget preview() {
return Text('Attributes');
}
```
Which is effectively the same as:
```dart
@Preview(name: 'Preview with wrapper')
Widget preview() {
return Provider<int>.value(
value: 42,
child: Text('Attributes'),
);
}
```
Finally, for situations where a `BuildContext` is needed, users can
return a `WidgetBuilder` from their preview function:
```dart
@Preview('Builder preview')
WidgetBuilder builderPreview() {
return (BuildContext context) {
// TODO: retrieve state from context.
return Text('Foo');
};
}
```
41c427c6de