Overriding BatThemeData

[Mastersam07]

Overview

With the regular theme instance, we are able to provide our own ThemeData to material app in the format:

theme: ThemeData(),
darkTheme: ThemeData()

Similarly, we can provide the BatThemeData to the Batcave in the format:

theme: BatThemeData(),
darkTheme: BatThemeData()

However, since all properties of BatThemeData are required, one has to provide them. The ideal way is to keep these properties null and copy them with defaults internally. However, this means one has to do a null check while calling properties from BatThemeData which isn't desirable. While the defaults might be returned, there should be no null checks. The flutter framework achieves this by doing:

  static ThemeData of(BuildContext context) {
    final _InheritedTheme? inheritedTheme = context.dependOnInheritedWidgetOfExactType<_InheritedTheme>();
    final MaterialLocalizations? localizations = Localizations.of<MaterialLocalizations>(context, MaterialLocalizations);
    final ScriptCategory category = localizations?.scriptCategory ?? ScriptCategory.englishLike;
    final ThemeData theme = inheritedTheme?.theme.data ?? _kFallbackTheme;
    return ThemeData.localize(theme, theme.typography.geometryThemeFor(category));
  }

which will always return a ThemeData instance. For us in the BatCave, we have done:

static BatThemeData of(BuildContext context) =>
      Theme.of(context).extension<BatThemeData>()!;

This means no null checks in calling the extensions; however, that doesn't remove the null check on the properties.

Expected behaviour

We should be able to define the theme in the form:

theme: BatThemeData(),
darkTheme: BatThemeData()

We should be able to call properties in the form BatThemeData.of(context).colors.primary as we currently do meaning no breaking change should be expected.