vp-k/flutter-craft/flutter-debugging

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

// Basic logging (truncates long output)
print('Debug: $value');
 
// No truncation (preferred)
debugPrint('Debug: $value');
 
// Conditional debug logging
import 'package:flutter/foundation.dart';
if (kDebugMode) {
  debugPrint('Only in debug mode: $value');
}
 
// Developer log with tags
import 'dart:developer';
log('API response', name: 'NetworkService', error: e);

# Open DevTools
flutter run --start-paused
# Then press 'd' or use DevTools button in IDE

// Show widget boundaries
debugPaintSizeEnabled = true;
 
// Show baseline alignments
debugPaintBaselinesEnabled = true;
 
// Show repaint regions
debugRepaintRainbowEnabled = true;

// Programmatic breakpoint
import 'dart:developer';
debugger();
 
// Or use IDE breakpoints

════════════════════════════════════════════════════════════
EXCEPTION CAUGHT BY WIDGETS LIBRARY
════════════════════════════════════════════════════════════
The following assertion was thrown building MyWidget:
'package:flutter/src/widgets/container.dart': Failed assertion: line 287
'child != null || decoration != null || constraints != null'
════════════════════════════════════════════════════════════

# Hot reload to reproduce
r  # in terminal
 
# Hot restart (clears state)
R  # in terminal
 
# Full restart
flutter run

# What changed recently?
git diff
 
# Recent commits
git log --oneline -10
 
# Diff with specific commit
git diff HEAD~3

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    debugPrint('=== MyWidget.build() ===');
    debugPrint('context.mounted: ${context.mounted}');
 
    final state = context.watch<MyState>();
    debugPrint('state: $state');
 
    return Container(...);
  }
}

# Search for similar working code
grep -r "similar_pattern" lib/

// Reference: Working widget
class WorkingWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocBuilder<WorkingBloc, WorkingState>(
      builder: (context, state) => ...,
    );
  }
}
 
// Broken: My widget
class BrokenWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // What's different?
    return BlocBuilder<MyBloc, MyState>(
      builder: (context, state) => ...,
    );
  }
}

// Before (broken)
Widget build(BuildContext context) {
  final bloc = context.read<MyBloc>();
  return ...;
}
 
// After (testing hypothesis)
Widget build(BuildContext context) {
  debugPrint('Looking for MyBloc...');
  try {
    final bloc = context.read<MyBloc>();
    debugPrint('Found: $bloc');
  } catch (e) {
    debugPrint('Error: $e');
  }
  return ...;
}

test('should return user when API succeeds', () async {
  // Arrange
  when(mockApi.getUser(any)).thenAnswer((_) async => userModel);
 
  // Act
  final result = await repository.getUser('123');
 
  // Assert
  expect(result, equals(userEntity));
});

// Fix the root cause identified in Phase 3
class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (_) => getIt<MyBloc>(),
      child: BlocBuilder<MyBloc, MyState>(...),
    );
  }
}

# Run analysis
flutter analyze
 
# Run tests
flutter test
 
# Manual verification
flutter run
# Test the specific scenario