widgetFactory top-level constant

_WidgetFactory const widgetFactory

Annotation which marks a function as a widget factory for the purpose of widget creation tracking.

When widget creation tracking is enabled, the framework tracks the source code location of the constructor call for each widget instance. This information is used by the DevTools to provide an improved developer experience. For example, it allows the Flutter inspector to present the widget tree in a manner similar to how the UI was defined in your source code.

Widget constructors are automatically instrumented to track the source code location of constructor calls. However, there are cases where a function acts as a sort of a constructor for a widget and a call to such a function should be considered as the creation location for the returned widget instance.

Annotating a function with this annotation marks the function as a widget factory. The framework will then instrument that function in the same way as it does for Widget constructors.

Tracking will not work correctly if the function has optional positional parameters.

Currently this annotation is only supported on extension methods.

{@tool snippet}

This example shows how to use the widgetFactory annotation to mark an extension method as a widget factory:

extension PaddingModifier on Widget {
  @widgetFactory
  Widget padding(EdgeInsetsGeometry padding) {
    return Padding(padding: padding, child: this);
  }
}

When using the above extension method, the framework will track the creation location of the Padding widget instance as the source code location where the padding extension method was called:

// continuing from previous example...
const Text('Hello World!')
    .padding(const EdgeInsets.all(8));

{@end-tool}

See also:

• the documentation for Track widget creation.

Implementation

// The below ignore is needed because the static type of the annotation is used
// by the CFE kernel transformer that implements the instrumentation to
// recognize the annotation.
// ignore: library_private_types_in_public_api
const _WidgetFactory widgetFactory = _WidgetFactory();