This article highlights five common Flutter errors developers often encounter—such as "A RenderFlex overflowed," "RenderBox was not laid out," "Vertical viewport was given unbounded height," "setState() called during build," and "ScrollController attached to multiple scroll views"—and provides quick, practical solutions like using Expanded, SizedBox, and proper state management. It also offers bonus tips on avoiding layout issues using tools like Flutter Inspector, SafeArea, and documentation. The goal is to help developers fix bugs faster and build more stable Flutter apps.
If you're building mobile apps with Flutter — whether you're just starting out or managing production apps — you've probably run into some confusing errors. The good news? Most of them have simple solutions once you understand what’s going on under the hood.
In this article, we’ll walk through five of the most common Flutter errors, why they happen, and the quick fixes to get your app back on track. Plus, we'll help you avoid these issues in the future, saving you time and frustration.
1. "A RenderFlex overflowed..."
🧠Why it happens:
You’ve used a Row or Column with child widgets that are too wide or tall for the available space. Flutter tries to fit them but can’t — resulting in the infamous yellow-black overflow stripes in debug mode.
✅ How to fix it:
Use Expanded or Flexible to make sure the child widgets scale within the available space.
2. "RenderBox was not laid out"
🧠Why it happens:
Your widget doesn’t know how big it should be. This usually happens when placing a widget without giving it constraints inside a Column, Row, or Stack.
✅ How to fix it:
Wrap it in a SizedBox, Expanded, or define a fixed height or width.
3. "Vertical viewport was given unbounded height"
🧠Why it happens:
You placed a scrollable widget (like ListView, SingleChildScrollView, etc.) inside a parent widget (usually a Column) without giving it a height. Flutter doesn't know how tall it should be.
✅ How to fix it:
Wrap it with an Expanded or a SizedBox with defined height.
4. "setState() called during build"
🧠Why it happens:
You call setState() inside the build() method, which leads to an infinite loop or unexpected behavior because every state change triggers a new build.
✅ How to fix it:
Use initState() for initial setup or call setState() inside interaction handlers like onTap, onPressed, etc.
5. "The ScrollController is attached to multiple scroll views"
🧠Why it happens:
You’re trying to use one ScrollController for more than one scrollable widget — which Flutter doesn’t allow.
✅ How to fix it:
Use a separate instance of ScrollController for each scroll view.
🧹 And don’t forget to dispose of them:
Bonus: How to Avoid Common Flutter Mistakes
✅ Use Layout Debug Tools:
Use Flutter’s layout tools like flutter inspector or enable debug painting with debugPaintSizeEnabled to visualize widget boundaries.
✅ Wrap with SafeArea:
Always consider wrapping widgets with SafeArea to prevent overlapping with system UI.
✅ Read Widget Documentation:
Flutter's official documentation is comprehensive. Always check how a widget handles constraints and layout.
Final Words: Build Flutter Apps Like a Pro
Flutter makes building beautiful UIs easy, but these common mistakes can trip up even experienced devs. Understanding how Flutter handles layout, state, and scrolling is key to mastering the framework.
By bookmarking this guide, you’re giving yourself a solid reference to handle these issues faster next time.
Keywords: Flutter common errors, Flutter error solutions, Flutter setState bug, RenderFlex overflow fix, Flutter ScrollController issue, Flutter layout problems, Common Flutter issues