From 9b7f6abd877cb8f39a01eae716919ae821436c4d Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Thu, 24 May 2018 18:23:13 -0700
Subject: [PATCH] Fabric: Support for `onLayout` event

Summary: `onLayout` event is fired when some layoutable node got inserted or updated (with changed layout) during commit phase.

Reviewed By: fkgozali

Differential Revision: D8119826

fbshipit-source-id: 831003c88fe5c4358a80328aa715be80e484b52e
---
 ReactCommon/fabric/uimanager/ShadowTree.cpp   | 42 +++++++++++++++++++
 ReactCommon/fabric/uimanager/ShadowTree.h     |  1 +
 ReactCommon/fabric/view/ViewEventHandlers.cpp | 14 +++++++
 ReactCommon/fabric/view/ViewEventHandlers.h   |  7 ++++
 4 files changed, 64 insertions(+)

diff --git a/ReactCommon/fabric/uimanager/ShadowTree.cpp b/ReactCommon/fabric/uimanager/ShadowTree.cpp
index 439369b9e55..4422b43c0c7 100644
--- a/ReactCommon/fabric/uimanager/ShadowTree.cpp
+++ b/ReactCommon/fabric/uimanager/ShadowTree.cpp
@@ -76,6 +76,8 @@ void ShadowTree::complete(UnsharedRootShadowNode newRootShadowNode) {
   );
 
   if (commit(newRootShadowNode)) {
+    emitLayoutEvents(instructions);
+
     if (delegate_) {
       delegate_->shadowTreeDidCommit(shared_from_this(), instructions);
     }
@@ -93,6 +95,46 @@ bool ShadowTree::commit(const SharedRootShadowNode &newRootShadowNode) {
   return true;
 }
 
+void ShadowTree::emitLayoutEvents(const TreeMutationInstructionList &instructions) {
+  for (auto &&instruction : instructions) {
+    auto &&type = instruction.getType();
+
+    // Only `Insertion` and `Replacement` instructions can affect layout metrics.
+    if (
+        type == TreeMutationInstruction::Insertion ||
+        type == TreeMutationInstruction::Replacement
+    ) {
+      auto &&newShadowNode = instruction.getNewChildNode();
+      auto &&eventHandlers = newShadowNode->getEventHandlers();
+      auto &&viewEventHandlers = std::dynamic_pointer_cast<const ViewEventHandlers>(eventHandlers);
+
+      // Checking if particular shadow node supports `onLayout` event (part of `ViewEventHandlers`).
+      if (viewEventHandlers) {
+        // Now we know that both (old and new) shadow nodes must be `LayoutableShadowNode` subclasses.
+        assert(std::dynamic_pointer_cast<const LayoutableShadowNode>(newShadowNode));
+        // TODO(T29661055): Consider using `std::reinterpret_pointer_cast`.
+        auto &&newLayoutableShadowNode =
+          std::dynamic_pointer_cast<const LayoutableShadowNode>(newShadowNode);
+
+        // In case if we have `oldShadowNode`, we have to check that layout metrics have changed.
+        if (type == TreeMutationInstruction::Replacement) {
+          auto &&oldShadowNode = instruction.getOldChildNode();
+          assert(std::dynamic_pointer_cast<const LayoutableShadowNode>(oldShadowNode));
+          // TODO(T29661055): Consider using `std::reinterpret_pointer_cast`.
+          auto &&oldLayoutableShadowNode =
+            std::dynamic_pointer_cast<const LayoutableShadowNode>(oldShadowNode);
+
+          if (oldLayoutableShadowNode->getLayoutMetrics() == newLayoutableShadowNode->getLayoutMetrics()) {
+            continue;
+          }
+        }
+
+        viewEventHandlers->onLayout(newLayoutableShadowNode->getLayoutMetrics());
+      }
+    }
+  }
+}
+
 #pragma mark - Delegate
 
 void ShadowTree::setDelegate(ShadowTreeDelegate *delegate) {
diff --git a/ReactCommon/fabric/uimanager/ShadowTree.h b/ReactCommon/fabric/uimanager/ShadowTree.h
index e2abea7a37c..cc20d697d68 100644
--- a/ReactCommon/fabric/uimanager/ShadowTree.h
+++ b/ReactCommon/fabric/uimanager/ShadowTree.h
@@ -76,6 +76,7 @@ private:
   UnsharedRootShadowNode cloneRootShadowNode(const LayoutConstraints &layoutConstraints, const LayoutContext &layoutContext) const;
   void complete(UnsharedRootShadowNode newRootShadowNode);
   bool commit(const SharedRootShadowNode &newRootShadowNode);
+  void emitLayoutEvents(const TreeMutationInstructionList &instructions);
 
   const Tag rootTag_;
   SharedRootShadowNode rootShadowNode_;
diff --git a/ReactCommon/fabric/view/ViewEventHandlers.cpp b/ReactCommon/fabric/view/ViewEventHandlers.cpp
index 261f38c3ab1..e673d077efb 100644
--- a/ReactCommon/fabric/view/ViewEventHandlers.cpp
+++ b/ReactCommon/fabric/view/ViewEventHandlers.cpp
@@ -24,5 +24,19 @@ void ViewEventHandlers::onAccessibilityMagicTap() const {
   dispatchEvent("magicTap");
 }
 
+#pragma mark - Layout
+
+void ViewEventHandlers::onLayout(const LayoutMetrics &layoutMetrics) const {
+  folly::dynamic payload = folly::dynamic::object();
+  auto &&frame = layoutMetrics.frame;
+  payload["layout"] = folly::dynamic::object
+    ("x", frame.origin.x)
+    ("y", frame.origin.y)
+    ("width", frame.size.width)
+    ("height", frame.size.height);
+
+  dispatchEvent("layout", payload);
+}
+
 } // namespace react
 } // namespace facebook
diff --git a/ReactCommon/fabric/view/ViewEventHandlers.h b/ReactCommon/fabric/view/ViewEventHandlers.h
index 3e8236b4b15..e72e41f345b 100644
--- a/ReactCommon/fabric/view/ViewEventHandlers.h
+++ b/ReactCommon/fabric/view/ViewEventHandlers.h
@@ -9,6 +9,7 @@
 #include <memory>
 
 #include <fabric/core/EventHandlers.h>
+#include <fabric/core/LayoutMetrics.h>
 
 namespace facebook {
 namespace react {
@@ -24,9 +25,15 @@ public:
 
   using EventHandlers::EventHandlers;
 
+#pragma mark - Accessibility
+
   void onAccessibilityAction(const std::string &name) const;
   void onAccessibilityTap() const;
   void onAccessibilityMagicTap() const;
+
+#pragma mark - Layout
+
+  void onLayout(const LayoutMetrics &layoutMetrics) const;
 };
 
 } // namespace react