RelativeScale is a simple custom sizing system for flutter widgets to achieve the same physical sizes across different devices.

It is VERY easy to use.

• sy(value) and sx(value)

• Example:

  • sy(10) - size relative to screen height.
  • sx(10) - size relative to screen width.

• RelativeBuilder - A builder widget that provides the scaling methods sy and sx.

• RelativeScale (deprecated) - A StatefulWidget mixin that provides the scaling methods sy and sx. It is highly recommended to use RelativeBuilder.

RelativeBuilder example.

class Example extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RelativeBuilder(
      builder: (context, height, width, sy, sx) {
        return Scaffold(
          appBar: AppBar(
            title: Text(
              'App Bar Title',
              style: TextStyle(fontSize: sy(13)),
            ),
          ),
          body: Container(
            height: height,
            width: width,
            child: Text(
              'Body Text',
              style: TextStyle(fontSize: sy(11)),
            ),
          ),
        );
      },
    );
  }
}

The base screen size for these widgets is 480 x 800. The source code for this preview app is here.

Now, look at these scaled widgets with RelativeScale. There is a difference, yeah, but that's because of the system scaled sizes like the AppBar (look at the appbar's height :) ). Now let's forget about that and focus on the texts and the rectangle containers. They are the same sizes.

Now, for unscaled sizes, no RelativeScale at all. Well, that's quite obvious :). Look at the texts on the last image, they are very small comparing to the first image. And the rectangle containers, very big difference.

The full example is in the Example section.

For instance, you have a container widget like this:

Container(
    height: 300,
    width: 500,
)

and you implemented RelativeScale:

Container(
    height: sy(300),
    width: sx(500),
)

they will not be the same size anymore, using relative scaler will make your sizes a bit bigger. But the hard work will payoff after adjusting your sizes because your app will now have the same widget sizes in every devices.

Please note that these scaler methods are relative to screen size. So basically in this case sy(50) and sx(50) is NOT the same size.

Also, another thing to note is that if you use sy for height and sx for width (or vice-versa), you'll get widgets with the same ratio (not size) which is still useful. The Scaled preview image above uses only sy, and containers and text have the same size across different screens.

Container(
    height: sy(300),
    width: sx(300),
)
// Yeah they are the same value "300", but they are not the same unit 'cause you used "sx" on the width.

Container(
    height: sy(300), // or sx(value)
    width: sy(300), // or sx(value)
)

The library doesn't support orientation yet. If you designed your app for portrait and the user rotates the app to landscape view, the sizes will be messed up. So if you want to use this library, it's highly recommended you lock the rotation. Or if your app should adapt to orientation, DO NOT use this library, there are a lot of alternatives.