Flyinsono/lib/lab/components/fixed_height_grid_delegate.dart

import 'package:flutter/rendering.dart';

class FixedHeightGridDelegate extends SliverGridDelegate {
  /// Creates a delegate that makes grid layouts with a fixed number of tiles in
  /// the cross axis.
  ///
  /// All of the arguments must not be null. The `mainAxisSpacing` and
  /// `crossAxisSpacing` arguments must not be negative. The `crossAxisCount`
  /// and `childAspectRatio` arguments must be greater than zero.
  const FixedHeightGridDelegate({
    required this.crossAxisCount,
    this.mainAxisSpacing = 0.0,
    this.crossAxisSpacing = 0.0,
    this.height = 56.0,
  })  : assert(crossAxisCount > 0),
        assert(mainAxisSpacing >= 0),
        assert(crossAxisSpacing >= 0),
        assert(height > 0);

  /// The number of children in the cross axis.
  final int crossAxisCount;

  /// The number of logical pixels between each child along the main axis.
  final double mainAxisSpacing;

  /// The number of logical pixels between each child along the cross axis.
  final double crossAxisSpacing;

  /// The height of the crossAxis.
  final double height;

  bool _debugAssertIsValid() {
    assert(crossAxisCount > 0);
    assert(mainAxisSpacing >= 0.0);
    assert(crossAxisSpacing >= 0.0);
    assert(height > 0.0);
    return true;
  }

  @override
  SliverGridLayout getLayout(SliverConstraints constraints) {
    assert(_debugAssertIsValid());
    final double usableCrossAxisExtent =
        constraints.crossAxisExtent - crossAxisSpacing * (crossAxisCount - 1);
    final double childCrossAxisExtent = usableCrossAxisExtent / crossAxisCount;
    final double childMainAxisExtent = height;
    return SliverGridRegularTileLayout(
      crossAxisCount: crossAxisCount,
      mainAxisStride: childMainAxisExtent + mainAxisSpacing,
      crossAxisStride: childCrossAxisExtent + crossAxisSpacing,
      childMainAxisExtent: childMainAxisExtent,
      childCrossAxisExtent: childCrossAxisExtent,
      reverseCrossAxis: axisDirectionIsReversed(constraints.crossAxisDirection),
    );
  }

  @override
  bool shouldRelayout(FixedHeightGridDelegate oldDelegate) {
    return oldDelegate.crossAxisCount != crossAxisCount ||
        oldDelegate.mainAxisSpacing != mainAxisSpacing ||
        oldDelegate.crossAxisSpacing != crossAxisSpacing ||
        oldDelegate.height != height;
  }
}