AdaptiveContainer class

A simplified declarative wrapper around ContainerQuery that displays different widgets based on the parent container's size tier.

Unlike screen-based breakpoints, AdaptiveContainer responds to the parent's actual constraints, making it ideal for reusable components that may appear in different-sized containers.

Performance Design

• Uses ContainerQuery internally (single LayoutBuilder per instance)
• Widget selection via array lookup — O(1) fallback chain
• No extra allocations — the widget array is created once per build

Fallback Behavior

If a widget for the current tier is null, falls back to the nearest smaller tier: xxl → xl → lg → md → sm → xs (always available).

Example

AdaptiveContainer(
  breakpoints: [300, 500, 700, 900, 1200],
  xs: CompactProductCard(),
  md: MediumProductCard(),
  lg: ExpandedProductCard(),
)