flutter-problem with tabbar height in the page

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01-10-2024

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Flutter TabBar Height Troubles: A Common Issue and Its Solution

Ever built a beautiful Flutter app with a TabBar, only to find its height isn't quite what you envisioned? This is a common issue many Flutter developers face, and it often stems from the default behavior of the TabBar widget. Let's dive into understanding this problem and how to achieve the desired height for your TabBar.

The Problem:

Imagine you have a TabBar at the top of your app screen, and you want it to be a specific height, say 50 pixels. You might try setting the preferredSize property of the TabBar widget to Size(double.infinity, 50), expecting it to adjust accordingly. However, the TabBar often stubbornly sticks to its default height, leaving you with a visual mismatch.

Here's a typical example:

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  late TabController _tabController;

  @override
  void initState() {
    super.initState();
    _tabController = TabController(length: 3, vsync: this);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("TabBar Height Issue"),
        bottom: TabBar(
          controller: _tabController,
          tabs: [
            Tab(text: 'Tab 1'),
            Tab(text: 'Tab 2'),
            Tab(text: 'Tab 3'),
          ],
          // This doesn't always work as expected!
          preferredSize: Size(double.infinity, 50), 
        ),
      ),
      body: TabBarView(
        controller: _tabController,
        children: [
          Center(child: Text('Tab 1')),
          Center(child: Text('Tab 2')),
          Center(child: Text('Tab 3')),
        ],
      ),
    );
  }

  @override
  void dispose() {
    _tabController.dispose();
    super.dispose();
  }
}

Why It Happens:

The preferredSize property of TabBar doesn't directly control its height. Instead, it defines the preferred size of the TabBar within its parent container (in this case, the AppBar). The AppBar often has its own constraints that influence the final size of the TabBar.

The Solution:

To achieve the desired height, you need to override the default behavior by either modifying the AppBar constraints or directly adjusting the TabBar size using a PreferredSize widget:

1. Modifying AppBar Constraints:

   • Wrap the AppBar with a PreferredSize widget and set its preferredSize to the desired height:

   appBar: PreferredSize(
     preferredSize: Size.fromHeight(50),
     child: AppBar(
       // ... your AppBar content
     ),
   ),
   

2. Directly Adjusting TabBar Size:

   • Wrap the TabBar with a PreferredSize widget and set its preferredSize to the desired height:

   appBar: AppBar(
     title: Text("TabBar Height Issue"),
     bottom: PreferredSize(
       preferredSize: Size.fromHeight(50),
       child: TabBar(
         // ... your TabBar content
       ),
     ),
   ),
   

Important Notes:

• The preferredSize property of the TabBar itself is still used to define the minimum size it wants to occupy within its parent widget.
• If you are using a custom AppBar widget, you might need to override its preferredSize method to return the desired height.
• Remember that the height of the TabBar will be affected by the size of its children (tabs) and other elements within the AppBar.

By understanding the nuances of the TabBar and AppBar widgets, you can effectively control the height of your TabBar and achieve the desired visual layout in your Flutter applications.