/* * Copyright (c) Meta Platforms, Inc. and affiliates. * * This source code is licensed under the MIT license found in the * LICENSE file in the root directory of this source tree. */ #include "updateMountedFlag.h" namespace facebook::react { void updateMountedFlag( const ShadowNode::ListOfShared& oldChildren, const ShadowNode::ListOfShared& newChildren) { // This is a simplified version of Diffing algorithm that only updates // `mounted` flag on `ShadowNode`s. The algorithm sets "mounted" flag before // "unmounted" to allow `ShadowNode` detect a situation where the node was // remounted. if (&oldChildren == &newChildren) { // Lists are identical, nothing to do. return; } if (oldChildren.empty() && newChildren.empty()) { // Both lists are empty, nothing to do. return; } size_t index = 0; // Stage 1: Mount and unmount "updated" children. for (index = 0; index < oldChildren.size() && index < newChildren.size(); index++) { const auto& oldChild = oldChildren[index]; const auto& newChild = newChildren[index]; if (oldChild == newChild) { // Nodes are identical, skipping the subtree. continue; } if (!ShadowNode::sameFamily(*oldChild, *newChild)) { // Totally different nodes, updating is impossible. break; } newChild->setMounted(true); oldChild->setMounted(false); updateMountedFlag(oldChild->getChildren(), newChild->getChildren()); } size_t lastIndexAfterFirstStage = index; // State 2: Mount new children. for (index = lastIndexAfterFirstStage; index < newChildren.size(); index++) { const auto& newChild = newChildren[index]; newChild->setMounted(true); updateMountedFlag({}, newChild->getChildren()); } // State 3: Unmount old children. for (index = lastIndexAfterFirstStage; index < oldChildren.size(); index++) { const auto& oldChild = oldChildren[index]; oldChild->setMounted(false); updateMountedFlag(oldChild->getChildren(), {}); } } } // namespace facebook::react