Sliver grid delegate for items with fixed height and minimum width

sliver_grid_fixed_height_delegate.dart

import 'dart:math' as math;

import 'package:flutter/rendering.dart';

class SliverGridDelegateWithFixedMainAxisExtent extends SliverGridDelegate {
  /// Creates a delegate that makes grid layouts with tiles that have a fixed
  /// main axis extent and a minimum cross axis extent. This delegate will
  /// attempt to fit as many items as possible in the cross axis while respecting
  /// the minimum width.
  ///
  /// All of the arguments must not be null.
  const SliverGridDelegateWithFixedMainAxisExtent({
    required this.mainAxisExtent,
    required this.minCrossAxisExtent,
    this.mainAxisSpacing = 0.0,
    this.crossAxisSpacing = 0.0,
  })  : assert(mainAxisExtent > 0),
        assert(minCrossAxisExtent > 0),
        assert(mainAxisSpacing >= 0),
        assert(crossAxisSpacing >= 0);

  /// The extend of tiles in the main axis
  final double mainAxisExtent;

  /// The minimum extent of tiles in the cross axis.
  ///
  /// This delegate will select a cross-axis extent for the tiles that is as
  /// small as possible subject to the following conditions:
  ///
  ///  - The extent evenly divides the cross-axis extent of the grid.
  ///  - The extent is at least [minCrossAxisExtent].
  ///
  /// For example, if the grid is vertical, the grid is 600.0 pixels wide, and
  /// [minCrossAxisExtent] is 180.0, this delegate will create a grid with 3
  /// columns that are 200.0 pixels wide.
  final double minCrossAxisExtent;

  /// 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;

  @override
  SliverGridLayout getLayout(SliverConstraints constraints) {
    final int crossAxisCount =
        (constraints.crossAxisExtent / (minCrossAxisExtent + crossAxisSpacing)).floor();
    final double usableCrossAxisExtent = math.max(
      0.0,
      constraints.crossAxisExtent - crossAxisSpacing * (crossAxisCount - 1),
    );
    final double childCrossAxisExtent = usableCrossAxisExtent / crossAxisCount;
    final double childMainAxisExtent = mainAxisExtent;
    return SliverGridRegularTileLayout(
      crossAxisCount: crossAxisCount,
      mainAxisStride: childMainAxisExtent + mainAxisSpacing,
      crossAxisStride: childCrossAxisExtent + crossAxisSpacing,
      childMainAxisExtent: childMainAxisExtent,
      childCrossAxisExtent: childCrossAxisExtent,
      reverseCrossAxis: axisDirectionIsReversed(constraints.crossAxisDirection),
    );
  }

  @override
  bool shouldRelayout(SliverGridDelegateWithFixedMainAxisExtent oldDelegate) {
    return oldDelegate.mainAxisExtent != mainAxisExtent ||
        oldDelegate.minCrossAxisExtent != minCrossAxisExtent ||
        oldDelegate.mainAxisSpacing != mainAxisSpacing ||
        oldDelegate.crossAxisSpacing != crossAxisSpacing;
  }
}