Flutter error: The body might complete normally, causing 'null' to be returned, but the re-CodePudding

import 'package:flutter/material.dart';

class LayOutBuilder extends StatelessWidget {
  const LayOutBuilder({super.key});

  @override
  Widget build(BuildContext context) {
    
    return Scaffold(
      body: LayoutBuilder(
      builder: (context, p1) {
        if (p1.maxHeight < 400) {
          return Container();
        }
      },
    ),
    );
  }
}

I dont know why it does not run.

CodePudding user response：

you're returning a Container only if p1.maxHeight < 400, but you didn't specify what to return if p1.maxHeight < 400 is not true, hence it will return null, and that's not allowed because it has to return something

if (p1.maxHeight < 400) {
  return Container();
} else {
  return Text('some widget');
}

CodePudding user response：

The builder argument needs to be a function that returns a Widget. Your implementation only returns a Widget under some if-condition. In the else-case, it does not return anything. This is not allowed and throws a compile error.

You should return a Widget in all cases. Which widget specifically depends on your use case. But something like this will compile:

return Scaffold(
  body: LayoutBuilder(
  builder: (context, p1) {
    if (p1.maxHeight < 400) {
      return Container();
    } else {
      return SizedBox(height: 0) // Or any other widget
    }
  }),
);