Vertical viewport was given unbounded height (again) in Flutter: Causes and How to Fix

Fixing the Unbounded Height Issue in Flutter

• Wrap the widget that needs to have an explicit height with a widget that gives it bounded height, like Container or SizedBox. This ensures that Flutter can calculate the height of the widget.

 

• If using a ListView, SingleChildScrollView, or other scrollable widget, specify constraints for these widgets. You can wrap them with a Container or SizedBox with a defined height or use properties like shrinkWrap: true.

Container(
  height: 300.0, // Example of giving a fixed height
  child: ListView(
    shrinkWrap: true, // Ensures the list view takes the space it requires
    children: <Widget>[
      // List items here
    ],
  ),
)

• Consider using Flexible or Expanded when working within a Column or Row to properly allocate available space. This will help distribute any extra space and resolve unbounded height issues.

Column(
  children: <Widget>[
    Expanded(
      child: SingleChildScrollView(
        child: Column(
          children: <Widget>[
            // Widgets that need to be inside scrollable area
          ],
        ),
      ),
    ),
  ],
)

• Make use of MediaQuery to make size constraints responsive and remove hard-coded values for height. This helps adapt your layout to different screen sizes.

Container(
  height: MediaQuery.of(context).size.height * 0.5, // 50% height of the screen
  child: CustomWidget(),
)

• For GridView or other complex combinations, use ConstrainedBox to apply specific limitations. This keeps the grid's height in check when infinite height constraints are suspected.

ConstrainedBox(
  constraints: BoxConstraints(
    maxHeight: 400.0, // Limit the maximum height
  ),
  child: GridView.count(
    crossAxisCount: 2,
    children: <Widget>[
      // Grid items here
    ],
  ),
)

• Sometimes, Flutter’s layout behavior can be clarified using debug messages. Turn on the debugPaintSizeEnabled flag to better understand what layout constraints your widgets are receiving and help diagnose where the issues lie.

// Add this line at the beginning of your main function
void main() {
  debugPaintSizeEnabled = true;
  runApp(MyApp());
}

Summary

• By wrapping problematic widgets with Container, SizedBox, setting the shrinkWrap property, or using Expanded/Flexible, you ensure widgets have the defined height they need for a stable layout.

 

• Adopt MediaQuery and ConstrainedBox for flexible yet bounded layouts.

 

• Using debugging tools like debugPaintSizeEnabled helps in visually identifying bounding areas and tackling the unbounded height issue directly.