SliverMainAxisGroup class

A sliver that places multiple sliver children in a linear array along the main axis, one after another.

Layout algorithm

This section describes how the framework causes RenderSliverMainAxisGroup to position its children.

Layout for a RenderSliverMainAxisGroup has four steps:

1. Keep track of an offset variable which is the total SliverGeometry.scrollExtent of the slivers laid out so far.
2. To determine the constraints for the next sliver child to layout, calculate the amount of paint extent occupied from 0.0 to the offset variable and subtract this from SliverConstraints.remainingPaintExtent minus to use as the child's SliverConstraints.remainingPaintExtent. For the SliverConstraints.scrollOffset, take the provided constraint's value and subtract out the offset variable, using 0.0 if negative.
3. Once we finish laying out all the slivers, this offset variable represents the total SliverGeometry.scrollExtent of the sliver group. Since it is possible for specialized slivers to try to paint itself outside of the bounds of the sliver group's scroll extent (see SliverPersistentHeader), we must do a second pass to set a SliverPhysicalParentData.paintOffset to make sure it is within the bounds of the sliver group.
4. Finally, set the RenderSliverMainAxisGroup.geometry with the total SliverGeometry.scrollExtent, SliverGeometry.paintExtent calculated from the constraints and SliverGeometry.scrollExtent, and SliverGeometry.maxPaintExtent.

See also:

• SliverPersistentHeader, which is a RenderObjectWidget which may require adjustment to its SliverPhysicalParentData.paintOffset to make it fit within the computed SliverGeometry.scrollExtent of the SliverMainAxisGroup.
• SliverCrossAxisGroup, which is the RenderObjectWidget for laying out multiple slivers along the cross axis.