Reconciler

Diffs successive virtual trees and applies the smallest set of native mutations that bring the on-screen view tree in line with the new description. The reconciler is platform-agnostic; it talks to native widgets exclusively through the NativeViewRegistry.

Virtual-tree reconciler.

Maintains a tree of VNode objects (each wrapping a native view) and diffs incoming Element trees to apply the minimal set of native mutations.

Supports:

• Native elements (type is a string like "Text").
• Function components (type is a callable decorated with component). Their hook state is preserved across renders.
• Provider elements (type == "__Provider__"), which push and pop context values during tree traversal.
• Error boundary elements (type == "__ErrorBoundary__"), which catch exceptions in child subtrees and render a fallback.
• Key-based child reconciliation for stable identity across re-renders.
• Post-render effect flushing. After each mount or reconcile pass, all queued effects are executed so they see the committed native tree.

Classes:

Name	Description
VNode	A mounted Element plus its native view.
Reconciler	Create, diff, and patch native view trees from Element descriptors.

VNode

VNode(element: Element, native_view: Any, children: List[VNode])

A mounted Element plus its native view.

The reconciler walks parallel trees of VNode and incoming Element to compute the minimal set of native mutations.

Attributes:

Name	Type	Description
element		The Element last rendered into this slot.
native_view		The platform-native view (e.g., an Android View or an iOS UIView). May be None for purely virtual wrappers such as providers and error boundaries.
children		Ordered list of child VNode instances.
hook_state	Any	The component's HookState when the node wraps a function component, otherwise None.

Reconciler

Reconciler(backend: Any)

Create, diff, and patch native view trees from Element descriptors.

After each mount or reconcile call the reconciler walks the committed tree and flushes all pending effects so effect callbacks run after native mutations are applied.

Parameters:

Name	Type	Description	Default
backend	Any	An object implementing the native-view protocol (create_view, update_view, add_child, remove_child, insert_child). PythonNative ships an Android backend and an iOS backend; tests can pass a mock.	required

Methods:

Name	Description
mount	Build native views from element and return the root native view.
reconcile	Diff new_element against the current tree and patch native views.

mount

mount(element: Element) -> Any

Build native views from element and return the root native view.

Parameters:

Name	Type	Description	Default
element	Element	The root Element to render.	required

Returns:

Type	Description
Any	The platform-native view that represents the root of the
Any	mounted tree.

reconcile

reconcile(new_element: Element) -> Any

Diff new_element against the current tree and patch native views.

Parameters:

Name	Type	Description	Default
new_element	Element	The desired root element after a state change.	required

Returns:

Type	Description
Any	The (possibly replaced) root native view.

Next steps

• Read the high-level walkthrough in Reconciliation.
• See how native widgets are registered in Native views.