android – AppBar height in Flutter-ThrowExceptions

Exception or error:

How can I get the height of an AppBar in Flutter?
I am using the MarialApp Widget (‘package:flutter/material.dart’).

I have the height of my Context and would like to deduct the height of the appbar.

final double height = MediaQuery.of(context).size.height;
How to solve:

This is not an ideal way, I think, but it will work.

Firstly declare the AppBar widget that you will use in your Scaffold.

Widget demoPage() {
  AppBar appBar = AppBar(
    title: Text('Demo'),
  );
  return Scaffold(
    appBar: appBar,
    body: /*
    page body
    */,
  );
}

Now you can get the height of your appBar using its preferredSized:

double height = appBar.preferredSize.height;

You can use this height to reduce from the screen height.

final double height = MediaQuery.of(context).size.height;

###

you can use this :

var height = AppBar().preferredSize.height;

this way is very sample and easy

###

There is a constant for the normal toolbar height: kToolbarHeight

###

You can get height of AppBar by using:

double height = appBar.preferredSize.height;

Make sure you have declared AppBar widget.

###

AppBar has a fixed height of 56.

You should create your own appbar implementing PreferredSizeWidget

class TestAppBar extends StatelessWidget implements PreferredSizeWidget {
  @override
  Widget build(BuildContext context) {
    return AppBar(
      title: Text('TEST'),
      centerTitle: true,
    );
  }

  @override
  Size get preferredSize => Size.fromHeight(34);
}

###

There is no need to store the AppBar instance, or to create a dummy one to get the height. Also, AppBar.preferredSize will always return the same value of 56.0, which is the standard of Material Design, and this value will not be always usable for some cases (it lacks the height of the status bar for example).

Since an AppBar is surely used with a Scaffold, IMHO, the smarter way to get the real AppBar height (the distance between the top of the device and the top of the Scaffold body) is to use:

double height = Scaffold.of(context).appBarMaxHeight;

With this, the computed height will include (independently of the platform):

  • The status bar height
  • The app bar height
  • The bottom app bar widget height if any (ex. TabBar)

Hope this will help!

###

Use preferred size

//defined as
Size preferredSize

preferred size is a size whose height is the sum of kToolbarHeight and the bottom widget’s preferred height.

Scaffold uses this size to set its app bar’s height.

It is defined like below in app bar class which implement PreferredSizeWidget

 preferredSize = new Size.fromHeight(kToolbarHeight + (bottom?.preferredSize?.height ?? 0.0))

a link for example …

https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/material/app_bar.dart

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