How to solve ‘RenderBox was not laid out:’ in Flutter in a Card Widget Conclusion

In this blog post, we will explore how to fix the ‘RenderBox was not laid out:’ error that occurs when using a TextFormField inside a Card widget in Flutter.

The Issue

When trying to use a TextFormField inside a Card widget, you may encounter the following error:

══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞══
I/flutter ( 5881): The following assertion was true: 
I/flutter ( 5881): RenderBox 'renderBox' had no layout information.
I/flutter ( 5881): This means that the box was not laid out during the last frame, and that makes sense because... 
I/flutter ( 5881): ...RenderBox is a widget that can be placed anywhere in the tree, so it doesn't have any layout constraints. The exception will continue to propagate up the tree.

This error occurs because the Row widget expands horizontally, and since the TextField also expands horizontally by default, there are no width constraints for the TextField, causing the error.

The Solution

To fix this issue, you need to provide width constraints for the TextFormField. There are several ways to do so:

Method 1: Using Expanded

Row(
  children: [
    Expanded(child: TextField()),
  ],
)

By wrapping the TextField in an Expanded widget, you are telling Flutter that this child should take up as much space as possible along the horizontal axis. This will provide the necessary width constraints for the TextFormField.

Method 2: Using Flexible

Row(
  children: [
    Flexible(child: TextField()),
  ],
)

Similar to Expanded, wrapping the TextField in a Flexible widget will also provide width constraints, but it allows the child to take up as much space as possible along both axes (horizontal and vertical).

### Method 3: Wrapping with Container or SizedBox

Row(
  children: [
    SizedBox(width: 100, child: TextField()),
  ],
)

Another way to provide width constraints is by wrapping the TextFormField in a Container or SizedBox widget. This will give you more control over the size of the widget and ensure that it has a minimum width.

Error Reasoning

The error occurs because the Row widget expands horizontally, and since the TextField also expands horizontally by default, there are no width constraints for the TextField. The RenderBox ‘renderBox’ had no layout information, meaning that the box was not laid out during the last frame.

In conclusion, the ‘RenderBox was not laid out:’ error in Flutter can be fixed by providing width constraints for a TextFormField inside a Card widget. This can be achieved using Expanded, Flexible, Container, or SizedBox widgets to ensure that the TextFormField has a minimum width.