Update GridView columns without rebuilding children

Here's an optimized solution to prevent GridView items from rebuilding during zoom gestures. The key is to use a combination of RepaintBoundary, ValueKey, and pre-cached items. The RepaintBoundary helps minimize repainting, while the ValueKey helps Flutter optimize rebuilds. By pre-generating and caching the items in initState(), we prevent unnecessary rebuilds when the grid layout changes. The solution also includes smooth zoom gestures that adjust the number of columns while maintaining item states. I've included a complete implementation that you can easily integrate into your project. The code uses proper state management to ensure efficient updates only when necessary.

import 'package:flutter/material.dart';

class ZoomableGridView extends StatefulWidget {
  final List<Widget> items;

  const ZoomableGridView({Key? key, required this.items}) : super(key: key);

  @override
  _ZoomableGridViewState createState() => _ZoomableGridViewState();
}

class _ZoomableGridViewState extends State<ZoomableGridView> {
  double _scale = 2.0;
  double _previousScale = 1.0;
  int _columns = 2;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onScaleStart: (details) {
        _previousScale = _scale;
      },
      onScaleUpdate: (details) {
        setState(() {
          // Calculate new scale with clamping
          _scale = (_previousScale * details.scale).clamp(1.0, 6.0);
          
          // Calculate new columns based on scale
          _columns = (6 - _scale).round().clamp(1, 6);
        });
      },
      onScaleEnd: (details) {
        _previousScale = 1.0;
      },
      child: GridView.builder(
        // Unique key to help Flutter optimize rebuilds
        key: ValueKey(_columns),
        
        // Customize grid delegate
        gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: _columns,
          mainAxisSpacing: 8,
          crossAxisSpacing: 8,
          childAspectRatio: 1.0, // Square items
        ),
        
        // Item count and builder
        itemCount: widget.items.length,
        itemBuilder: (context, index) {
          // Wrap each item with RepaintBoundary
          return RepaintBoundary(
            child: widget.items[index],
          );
        },
      ),
    );
  }
}

// Example Usage
class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Create a list of items to display in the grid
    final List<Widget> gridItems = List.generate(
      20, 
      (index) => _GridItemWidget(index: index),
    );

    return Scaffold(
      appBar: AppBar(title: Text('Zoomable GridView')),
      body: ZoomableGridView(items: gridItems),
    );
  }
}

// Custom grid item widget to demonstrate state preservation
class _GridItemWidget extends StatefulWidget {
  final int index;

  const _GridItemWidget({Key? key, required this.index}) : super(key: key);

  @override
  __GridItemWidgetState createState() => __GridItemWidgetState();
}

class __GridItemWidgetState extends State<_GridItemWidget> {
  bool _isSelected = false;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        setState(() {
          _isSelected = !_isSelected;
        });
      },
      child: Container(
        decoration: BoxDecoration(
          color: _isSelected 
            ? Colors.blue.shade200 
            : Colors.blue.shade100,
          borderRadius: BorderRadius.circular(10),
        ),
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Text(
                'Item ${widget.index}',
                style: TextStyle(
                  fontWeight: FontWeight.bold,
                  color: Colors.white,
                ),
              ),
              SizedBox(height: 8),
              Icon(
                _isSelected ? Icons.check_circle : Icons.circle_outlined,
                color: Colors.white,
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Let me know if you need any clarification or have questions about specific parts of the implementation!