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>

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→leaf order. The render object iterates this from index 0 (shallowest, painted last so it lands on top).

no setter

maxStickyDepth ↔ int

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}) → void

Computes sticky headers based on scroll position, populating headers and the per-nid lookup. Called after Pass 2 when actual extents and offsets are available. overlap is constraints.overlap — the number of pixels at the top covered by a preceding pinned sliver (e.g. PinnedHeaderSliver).

identifyPotentialStickyNodes({required double scrollOffset, required double overlap, required List<TKey> visibleNodes, required Float64List nodeOffsetsByNid, required Float64List nodeExtentsByNid, required FindFirstVisibleIndex findFirstVisibleIndex}) → Set<TKey>

Lightweight pre-pass that identifies nodes which might need to be sticky. Used before Pass 2 to force-create their render objects.

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).

purgeExitingDuringThrottle() → void

During a throttle-skip frame, drop sticky entries whose node just entered exiting state. Without this, a stale pinned row would keep painting / inflating paintExtent for another 1–2 frames until the next non-throttled recompute.

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.

shouldRecomputeThisFrame({required bool hasActiveAnimations, required double scrollOffset}) → bool

Returns true when sticky should be recomputed this frame. The throttle keeps mid-animation frames cheap (every third frame) but fires on every scroll, since stale pinnedY values produce visible jitter and wrong hit-test coordinates.

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