StickyHeaderComputer<TKey, TData> class

Computes sticky headers and owns the scratch state required for the computation. The owning render object hands in the per-frame inputs (visible nodes, layout-space offsets and extents, scroll position) and reads back the computed headers / infoForNid for paint, hit-test, and transform.

The computer is layout-state-shaped: a single instance is long-lived per render object and mutated in place each layout. Reset it via reset when the underlying controller swaps.

Constructors

StickyHeaderComputer({required TreeController<TKey, TData> controller, int maxStickyDepth = 0})

Properties

controller ↔ TreeController<TKey, TData>

The controller the probe reads structure, depths and extents from. Re-bindable so one computer survives a controller swap; assigning the same instance is a no-op. Pair a real swap with reset, which drops state keyed to the old controller's nids.

getter/setter pair

dirty ↔ bool

Whether sticky subtree precomputation needs to re-run. Set on structure change, extent change, or animation-to-idle transition; cleared by precomputeStableSubtreeBottoms.

getter/setter pair

hashCode → int

The hash code for this object.

no setter, inherited

headers → List<StickyHeaderInfo<TKey>>

All sticky headers in root-to-leaf order. The render object iterates this from index 0 (shallowest, painted last so it lands on top).

no setter

maxStickyDepth ↔ int

How many ancestor levels may pin at once. Zero disables sticky headers entirely, and is the candidate probe's first early-out.

getter/setter pair

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

computeStickyHeaders({required double scrollOffset, required double overlap, required List<TKey> visibleNodes, required Float64List nodeOffsetsByNid, required Float64List nodeExtentsByNid, required FindFirstVisibleIndex findFirstVisibleIndex, double freshOffsetAt(int visibleIndex)?}) → Set<TKey>

Computes the sticky set for this layout, populating headers and the per-nid lookup, and returns the candidate keys so the caller can force-create any that are outside the cache region.

infoForNid(int nid) → StickyHeaderInfo<TKey>?

Sticky info for nid, or null when the node is not currently sticky. Hot-path lookup used by paint transform and retention checks.

invalidatePrecompute() → void

Forces the next layout to take the per-candidate fallback path instead of the precomputed-array path. Used during animation frames where the cached subtree bottoms are stale.

isSticky(int nid) → bool

Whether nid is currently sticky.

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

precomputeStableSubtreeBottoms({required List<TKey> visibleNodes, required Float64List nodeOffsetsByNid, required Float64List nodeExtentsByNid}) → void

Precomputes subtree bottom offsets for all visible nodes in O(N).

reset() → void

Resets every piece of layout-derived state to the empty defaults the render object uses on first layout. Call when the controller swaps or the render object is hot-reloaded.

resizeForCapacity(int nidCapacity) → void

Grows the nid-indexed sticky array to match the controller's current nid capacity. Called from the render object's layout-array growth path so all per-nid arrays stay in lockstep.

resizeScratchArrays(int capacity) → void

Pre-allocates scratch arrays for capacity nodes. Useful when the tree size is known upfront to avoid incremental resizing.

toString() → String

A string representation of this object.

inherited

trimScratchArrays() → void

Reallocates scratch arrays to fit _lastPrecomputedCount (or empty if zero). Call when the tree shrinks significantly and memory matters.

Operators

operator ==(Object other) → bool

The equality operator.

inherited