SliverGridDelegateWithFixedCrossAxisCountcrossAxisCount

SliverGridDelegate is an abstract class in Flutter that describes how a grid of children should be laid out inside a sliver. It participates in the layout of grid-based slivers, such as SliverGrid, and works with a SliverChildDelegate to place and build children. A delegate receives the constraints of the scrollable area and reports a SliverGridLayout that determines the position and size of each child. The layout strategy is provided by concrete implementations and can adapt to changes in screen size, orientation, or other layout constraints.

Two common concrete implementations provide typical patterns for grid layouts. SliverGridDelegateWithFixedCrossAxisCount fixes the number of columns across the cross axis and allows configuration of mainAxisSpacing, crossAxisSpacing, and childAspectRatio. SliverGridDelegateWithMaxCrossAxisExtent determines the column count by a maximum cross-axis extent per child, while also supporting spacing and aspect settings. Both implementations define how the grid allocates space and places items along the cross and main axes.

The grid delegate can signal when a relayout is needed, via shouldRelayout, enabling efficient updates when inputs change. This helps optimize performance during size changes or device rotations.

Usage typically involves passing a gridDelegate to a SliverGrid inside a CustomScrollView or other sliver-containing scroll view, together with a SliverChildDelegate that provides the actual children. The SliverGridDelegate itself does not supply content; it defines the grid’s geometry, while the child delegate supplies the widgets.