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The `theme` parameter of `Preview(...)` allows for developers to provide a callback that returns a `PreviewThemeData` instance which can contain theming data for Material and Cupertino widgets in both light and dark modes. The provided theme data will be injected into the widget tree and applied to the previewed widget. The `brightness` parameter allows for developers to specify an initial brightness setting (e.g., light vs dark mode) for the previewed widget. If not provided, the current system default is used. A new button has also been added to each widget preview card that allows for toggling between light and dark mode for individual previews. **Demo:** https://github.com/user-attachments/assets/f0a4a3bc-25d2-49b0-a5f6-9149eccfc1d4 Fixes https://github.com/flutter/flutter/issues/166436 Fixes https://github.com/flutter/flutter/issues/166275 Fixes https://github.com/flutter/flutter/issues/166279 Fixes https://github.com/flutter/flutter/issues/166437
Token Defaults Generator
Script that generates component theme data defaults based on token data.
Usage
Run this program from the root of the git repository:
dart dev/tools/gen_defaults/bin/gen_defaults.dart [-v]
This updates generated/used_tokens.csv and the various component theme files.
Templates
There is a template file for every component that needs defaults from
the token database. These templates are implemented as subclasses of
TokenTemplate. This base class provides some utilities and a structure
for adding a new block of generated code to the bottom of a given file.
Templates need to override the generate method to provide the generated
code block as a string.
See lib/fab_template.dart for an example that generates defaults for the
Floating Action Button.
Tokens
Tokens are stored in JSON files in data/, and are sourced from
an internal Google database.
template.dart should provide nearly all useful token resolvers
(e.g. color, shape, etc.). For special cases in which one shouldn't
be defined, use getToken to get the raw token value. The script, through
the various revolvers and getToken, validates tokens, keeps track of
which tokens are used, and generates generated/used_tokens.csv.