[Solved] setState() or markNeedsBuild() called during build Error: A Comprehensive Guide
Introduction
When developing a Flutter application, developers often encounter errors that can hinder the smooth functioning of their app. One common error that users frequently face is the “[setState() or markNeedsBuild() called during build]” error. In this article, we will delve into the causes of this error, examine code examples, and provide solutions to resolve it.
What Causes the Error?
The `[setState() or markNeedsBuild() called during build]` error occurs when the `setState()` method or `markNeedsBuild()` function is called during the `build()` method. This is because Flutter’s stateful widget, `build()`, is designed to run only once, and it should not contain any complex computations that modify the state.
Here are the key reasons why this error occurs:
- Calling setState during build: Attempting to call `setState()` within the `build()` method can cause an infinite recursion, as the state will be updated, and rebuilding will start, only to be followed by another attempt to update the state.
- markNeedsBuild during build: When `markNeedsBuild()` is called inside the `build()` method, it notifies the framework that the widget needs to be rebuilt. However, calling it during the build process will cause the widget to enter an infinite loop.
Use Case Example
Suppose we have a stateful widget, `Counter`, where we try to increment the counter by 1 in the `build()` method:
“`dart
class _CounterState extends State
int _counter = 0;
@override
Widget build(BuildContext context) {
setState(() { // Error: setState called during build
_counter++;
});
return Text(‘You have clicked the button this many times: $_counter’);
}
}
“`
In this example, calling `setState()` during the `build()` method triggers an error, preventing the app from compiling.
Solutions to Resolve the Error
Here are two ways to fix the `[setState() or markNeedsBuild() called during build]` error:
1. Move Computation to a Non-Build Context
Instead of computing and updating the state within the `build()` method, use a separate method that’s not part of the widget’s `build()` function. This way, you avoid modifying the state during the build process.
“`dart
class _CounterState extends State
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Column(
children: [
Text(‘You have clicked the button this many times: $_counter’),
ElevatedButton(onPressed: _incrementCounter, child: Text(‘Increment’)),
],
);
}
}
“`
2. Use Futures or Scheduler for Complex Computations
If your computation involves futures, promises, or asynchronous operations, handle it in a separate method, avoiding complex computations within the `build()` method.
“`dart
class _CounterState extends State
int _counter = 0;
Future
// Complex computation that relies on async operations
await Future.delayed(Duration(milliseconds: 100));
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Column(
children: [
Text(‘You have clicked the button this many times: $_counter’),
ElevatedButton(onPressed: _computeCounterIncrement, child: Text(‘Increment’)),
],
);
}
}
“`
Additional Tips and Considerations
In addition to the solutions above, keep the following best practices in mind to avoid similar errors in your Flutter application:
- Ensure that any computations or modifications to the state are done outside the `build()` or within a separate method.
- Avoid complex computations or modifying the state within the `build()` method to prevent infinite recursion.
- Use futures or a scheduler for complex asynchronous operations.
FAQs
Q: Why am I getting this error?
A: The `[setState() or markNeedsBuild() called during build]` error occurs due to complex computations or state modifications within the `build()` method.
Q: How can I prevent this error?
A: Move computations or state modifications to a separate method, and avoid calling `setState()` or `markNeedsBuild()` within the `build()` method.
Q: What are some best practices for preventing similar errors?
A: Use a future or scheduler for complex asynchronous operations, avoid calling `setState()` or `markNeedsBuild()` within the `build()` method, and move computations or state modifications to separate methods.
Q: Can I call `setState()` within a widget’s `initState()` method?
A: Yes, you can call `setState()` within a widget’s `initState()` method, as it is not part of the widget’s build process.
Q: Can I call `setState()` within a widget’s `dispose()` method?
A: No, you should not call `setState()` within a widget’s `dispose()` method, as it is part of the widget’s lifecycle and could result in an infinite loop.
In conclusion, the `[setState() or markNeedsBuild() called during build]` error is typically caused by complex computations or state modifications within the `build()` method. By moving these computations to separate methods and avoiding calling `setState()` or `markNeedsBuild()` within the `build()` method, you can resolve this error and prevent similar issues in your Flutter application.
