How to create reusable Flutter app bar with dynamic value

Question

I'm trying to create a reusable app bar that has a dynamic size. I am using dynamic values to adjust the size of icons, padding, text font size, etc in the app and want to do the same with the app bar size. The app bar code below works dynamically and gives me the behavior I want using MediaQuery.

class SamplePage extends StatelessWidget {
  const SamplePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final screenHeight = MediaQuery.of(context).size.height;
    return Scaffold(
      appBar: AppBar(
        actions: const [
          BrandPopUpMenu(),
        ],
        automaticallyImplyLeading: true,
        centerTitle: true,
        title: const AppBarText(
          pageName: PageName.nutrition,
        ),
        toolbarHeight: screenHeight / 15.07,
      ),
      drawer: const SideSheet(),
      body: Container(),
    );
  }
}

When I try to create a reusable app bar from the code above that is when I run into trouble.

class SamplePage extends StatelessWidget {
  const SamplePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final screenHeight = MediaQuery.of(context).size.height;
    return Scaffold(
      appBar: SamplePageDynamicAppBar(screenHeight: screenHeight),
      drawer: const SideSheet(),
      body: Container(),
    );
  }
}

The code below only works with a hard coded preferred size and I am uncertain how to continue to use the dynamic value in the toolBarHeight and not the preferred size in the override.

class SamplePageDynamicAppBar extends StatelessWidget
    implements PreferredSizeWidget {
  const SamplePageDynamicAppBar({
    Key? key,
    required this.screenHeight,
  }) : super(key: key);

  final double screenHeight;

  @override
  Size get preferredSize => const Size.fromHeight(56.0);
  
  @override
  Widget build(BuildContext context) {
    return AppBar(
      actions: const [
        BrandPopUpMenu(),
      ],
      automaticallyImplyLeading: true,
      centerTitle: true,
      title: const AppBarText(
        pageName: PageName.nutrition,
      ),
      toolbarHeight: screenHeight / 15.07,
    );
  }
}

Any help will be greatly appreciated. Thanks

user2301346 · Accepted Answer · 2022-03-27 17:14:20Z

Since all you're doing is overriding toolbarHeight property of AppBar, see if this works. It extends AppBar instead creating a new widget. https://dartpad.dev/?id=d15b4d91168e13b89e86267da4311683

class SamplePageDynamicAppBar extends AppBar {
  SamplePageDynamicAppBar({Key? key, required double screenHeight}) :
    super(
      actions: const [
        BrandPopUpMenu(),
      ],
      automaticallyImplyLeading: true,
      centerTitle: true,
      title: const AppBarText(
        pageName: PageName.nutrition,
      ),
      toolbarHeight: screenHeight / 15.07,
    );
}

Alternatively you can use the code you've written by changing your implementation of the perferredSize getter. https://dartpad.dev/?id=758db4b7a7b2908b166a6a29d766045d

class SamplePageDynamicAppBar extends StatelessWidget implements PreferredSizeWidget {
  const SamplePageDynamicAppBar({
    Key? key,
    required double screenHeight,
  }) : 
    toolbarHeight = screenHeight / 15.07,    
    super(key: key);

  final double toolbarHeight;

  @override
  Size get preferredSize => Size.fromHeight(toolbarHeight);
 
  @override
  Widget build(BuildContext context) {
    return AppBar(
      actions: const [
        BrandPopUpMenu(),
      ],
      automaticallyImplyLeading: true,
      centerTitle: true,
      title: const AppBarText(
        pageName: PageName.nutrition,
      ),
      toolbarHeight: toolbarHeight,
    );
  }
}

Tyler2P · Accepted Answer · 2022-03-27 18:46:14Z

2

Try wrapping your custom AppBar with a PreferredSize widget when you reference it in your scaffold as follows, not passing through your preferred height and rather declaring it as part of the PreferredSize widget:

class SamplePage extends StatelessWidget {
  const SamplePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final screenHeight = MediaQuery.of(context).size.height;
    return PreferredSize(
      preferredSize: Size.fromHeight(screenHeight / 15.07),
      child: Scaffold(
        appBar: SamplePageDynamicAppBar(),
        drawer: const SideSheet(),
        body: Container(),
      ),
    );
  }
}

edited Mar 27, 2022 at 18:46

Tyler2P

2,37030 gold badges26 silver badges34 bronze badges

answered Mar 27, 2022 at 16:23

Noah Joshua

1061 silver badge3 bronze badges

1 Comment

Carleton Y Over a year ago

Thanks @noah. This helps a lot and teaches me a new approach I was unaware of before now.

Collectives™ on Stack Overflow

How to create reusable Flutter app bar with dynamic value

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related