Photo by Hamed Daram on Unsplash

Why You Should Be Using Flutter Theme Extensions

So I was thinking about writing an article about Flutter Theme Extensions. But there’s really not much to say about them. First you make a ThemeExtension class:

@immutable
class Foo extends ThemeExtension<Foo> {
 const Foo({
  …
 });
 @override
 Foo copyWith({
  …,
 }) {
  return Foo(
   …
  );
 }
 @override
 Foo lerp(ThemeExtension<Foo>? other, double t) {
  return Foo(…);
 }

Then whenever you make a theme you insert your custom theme data using copyWith()

ThemeData.dark().copyWith(
 extensions: <ThemeExtension<dynamic>>[
  Foo(…),
 ],
),

And then finally you retrieve it using extension()

Theme.of(context).extension<Foo>()!;

Easy peasy. So I’m not going to focus on that. Instead I’m going to focus on another question: why you should be using theme extensions in the first place?

Why You Should Never Save You Widgets

So you may have noticed in Flutter build() returns a Widget. And a Widget is an object. And objects can be saved to variables. So maybe instead of building a widget every single time you can cache the widget.