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There are currently 2 builders in flutter_design_codegen:

  • Design builder: generates the *.design.dart part file that contains the component page fields.
  • Page factory builder: generates a single file that aggregates all generated components into a single importable field.

Design builder

The design builder scans the dart files for classes annotated with @Design or @design. Once it finds it, it will generate a component page using the convention: generated{Folder1}{Folder2}{...}{Filex}{WidgetName}Page.

The id of the component will be the class name in camelCase. The title will be by default the widget's name, unless provided by the @Design annotation. Both subtitle, description is omitted if not provided by @Design.

Component section

A component section named after the constructor will be created for the each public constructor of the class. The section contains a ViewerWidgetBuilder which contains all the meta data required to construct the widget using its constructor. The builder will scan all the fields (optional, named, positional, etc.) and store their metadata into a fieldMetaDataset field so later the designer would know how to construct thoses fields using DataBuilders.

Note that the fieldMetaDataset will take into account whether the field is nullable/optional, the provided viewer initial values, via @DesignField(parameter: ...).


Currently not all types are mapped configured the default data builders (if no data builder is configured for a specific type, the widget designer will throw an error during runtime). To see the currently by default configured data builders, check the default_data_builders.dart file.

Note that you can always provide your own data builder configuration for a specific type. However some types are not fully supported yet, such as Function with parameters. You can find all limitations listed in FAQ: known limitations.

Futuremore, the source code of the constructor will be extracted into a source code snippet that will be shown along the widget in the designer.


The source is extracted using the analyzer via the abstract syntax tree (AST) and formatted using dart_style with some auto injected commas. Hence the code might be a bit different than what you have actually written, e.g. the comments are gone, the formatting might be different, etc.

A parameter builder class named _${NAME_OF_CONSTRUCTOR_IN_PASCAL_CASE}ParamBuilder will also be generated for each constructor. It can be used to configure the examples: if a constructor is annotated with @DesignExamples, component example subsection will be generated for each DesignExample. The generated sub section has a similar structure to the component section where the user can configure the initial values of each field.

API docs section

Finally, if the showApiDocs is true in the annotation (by default it is true), a section called API reference will be created which shows all the meta data previously collected on the constructor.

Page factory builder

Similar to the design builder, the page factor builder scans all dart files for classes with the @Design or @design annotation. It then aggregates it, with an import statement for each file, the component page fields into a single field: generatedComponentPages which can be used to import your component pages to the designer.


You can also include pages that are not generated, for instance to create your own component pages manually using the ViewerDocumentPage with a ViewerComponentSection section from flutter_design. To do that, you need to specify a valid namespace for the component using the same convention mentioned in Annotation and inject it together with the generated component pages when you pass it to the designer

pageGroups: [

Note that by default the pages are sorted by namespace/id names.