Multiple ways to solve RenderFlex overflow issues in Flutter

Overflow issues in Flutter, known as RenderFlex overflow can be quite common at the beginning. However, once you understand what is happening, fixing them becomes easy. In this post, we will explore different ways to solve these issues in Flutter. We will start by understanding how these issues can occur and then discuss the possible solutions.

Producing the RenderFlex Overflow

In the following main.dart file, there is a RenderFlex overflow issues caused by two Container widgets placed inside a Column widget, see the code below:

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Container Overflow Demo'),
        ),
        body: Column(
          children: [
            Container(
              color: Colors.green,
              height: 400,
              width: MediaQuery.of(context).size.width,
            ),
            Container(
              color: Colors.red,
              height: 400,
              width: MediaQuery.of(context).size.width,
            ),
          ],
        ),
      ),
    );
  }
}

The RenderFlex overflow occurs because both Container widgets have a height of 400, which exceeds the available screen size. Which makes the last Container widget goes outside of our screen.

1. Using the SingleChildScrollView widget

The first and easiest solution involves using the SingleChildScrollView widget. By wrapping our Column widget with it, we can make the content scrollable.

body: SingleChildScrollView(
  child: Column( ... ),
),

In the code snippet above, we just put our Column widget inside the SingleChildScrollView widget. By doing this, we fixed the RenderFlex issue and we are now able to see both our Container widgets.

This solution is perfect if you do not mind the user having to scroll down to see the rest of the available content.

2. Using the expanded widget

The Expanded widget can be used to make sure that our Container widgets only take the available space, see the code below:

body: Column(
  children: [
    Container(
      color: Colors.green,
      height: 400,
      width: MediaQuery.of(context).size.width,
    ),
    Expanded(
      child: Container(
        color: Colors.red,
        width: MediaQuery.of(context).size.width,
      ),
    ),
  ],
),

In this code snippet, we wrapped our second Container widget with the Expanded widget. We also removed the height property because the height of our Container widget is now limited to the remaining height.

As you can see, the second Container widget now uses only the remaining height.

However, this makes the Container smaller. To improve this, we can divide the space evenly by also wrapping the first Container widget with the Expanded widget:

body: Column(
  children: [
    Expanded(
      child: Container(
        color: Colors.green,
        width: MediaQuery.of(context).size.width,
      ),
    ),
    Expanded(
      child: Container(
        color: Colors.red,
        width: MediaQuery.of(context).size.width,
      ),
    ),
  ],
),

In this code snippet, we used the Expanded widget for both Container widgets and removed the height property from both. As a result, both Container widgets now have equal heights.

3. Using the MediaQuery class

The last solution involves using the MediaQuery class to dynamically calculate the height for our Container widgets. This approach is more technical, but it can be useful when the previous solutions do not meet your requirements.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final height = (MediaQuery.of(context).size.height -
        MediaQuery.of(context).padding.top -
        kToolbarHeight);

    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Center(
            child: Text('kToolbarHeight: ${kToolbarHeight.toString()}'),
          ),
        ),
        body: Column(
          children: [
            Container(
              color: Colors.green,
              height: height * 0.5,
              width: MediaQuery.of(context).size.width,
              child: Center(
                child: Text(
                  (height * 0.5).toString(),
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ),
            Container(
              color: Colors.red,
              height: height * 0.5,
              width: MediaQuery.of(context).size.width,
              child: Center(
                child: Text(
                  (height * 0.5).toString(),
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

In the code snippet, we create a variable called height that calculates the available height for the Container widgets. We do this by subtracting the top padding (obtained from MediaQuery.of(context).padding.top) and the height of the AppBar widget (using kToolbarHeight) from the total screen height (accessed through MediaQuery.of(context).size.height).

For both Container widgets, we set their height to 50% of the calculated height. To demonstrate the calculations, I have included Text widgets with the height values.

If you want more information about retrieving the height of the AppBar widget and its padding check out my related post: How to get the height of the AppBar and its padding in Flutter

Conclusion

We have looked at different ways to fix RenderFlex overflow issues in Flutter. The first solution makes the content scrollable using the SingleChildScrollView widget. Another option is to use the Expanded widget, which ensures that Container widgets share the available space. At last, we explored using the MediaQuery class to calculate the height dynamically based on screen size, padding, and AppBar height. With this knowledge, you are now able to solve RenderFlex overflow issues on your own.

Tijn van den Eijnde
Tijn van den Eijnde
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