From 402ae2f01fd91051be5b717b0578e18b863854af Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Tue, 20 Feb 2018 22:11:55 -0800
Subject: [PATCH] New UIManager API allowing intercept/delay mounting process

Summary: In some embedding/interop cases (RN inside, something else outside), the interop layer has to have the ability to control (intercept, delay, perform synchronously with another stuff) mounting process. This API allows doing that.

Reviewed By: fkgozali

Differential Revision: D7014179

fbshipit-source-id: 04036095f7e60a5ff7e69025ff6066fea92eb361
---
 React/Modules/RCTUIManager.m                  | 31 ++++++++++++++-----
 .../Modules/RCTUIManagerObserverCoordinator.h |  9 ++++++
 .../RCTUIManagerObserverCoordinator.mm        | 14 +++++++++
 3 files changed, 46 insertions(+), 8 deletions(-)

diff --git a/React/Modules/RCTUIManager.m b/React/Modules/RCTUIManager.m
index 1ea715c94..5dcce4658 100644
--- a/React/Modules/RCTUIManager.m
+++ b/React/Modules/RCTUIManager.m
@@ -1081,6 +1081,26 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
     return;
   }
 
+  __weak typeof(self) weakSelf = self;
+
+   void (^mountingBlock)(void) = ^{
+    typeof(self) strongSelf = weakSelf;
+
+    @try {
+      for (RCTViewManagerUIBlock block in previousPendingUIBlocks) {
+        block(strongSelf, strongSelf->_viewRegistry);
+      }
+    }
+    @catch (NSException *exception) {
+      RCTLogError(@"Exception thrown while executing UI block: %@", exception);
+    }
+  };
+
+  if ([self.observerCoordinator uiManager:self performMountingWithBlock:mountingBlock]) {
+    completion();
+    return;
+  }
+
   // Execute the previously queued UI blocks
   RCTProfileBeginFlowEvent();
   RCTExecuteOnMainQueue(^{
@@ -1088,14 +1108,9 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
     RCT_PROFILE_BEGIN_EVENT(RCTProfileTagAlways, @"-[UIManager flushUIBlocks]", (@{
       @"count": [@(previousPendingUIBlocks.count) stringValue],
     }));
-    @try {
-      for (RCTViewManagerUIBlock block in previousPendingUIBlocks) {
-        block(self, self->_viewRegistry);
-      }
-    }
-    @catch (NSException *exception) {
-      RCTLogError(@"Exception thrown while executing UI block: %@", exception);
-    }
+
+    mountingBlock();
+
     RCT_PROFILE_END_EVENT(RCTProfileTagAlways, @"");
 
     RCTExecuteOnUIManagerQueue(completion);
diff --git a/React/Modules/RCTUIManagerObserverCoordinator.h b/React/Modules/RCTUIManagerObserverCoordinator.h
index 83478b602..fc4064027 100644
--- a/React/Modules/RCTUIManagerObserverCoordinator.h
+++ b/React/Modules/RCTUIManagerObserverCoordinator.h
@@ -9,6 +9,8 @@
 
 #import <React/RCTViewManager.h>
 
+typedef dispatch_block_t RCTUIManagerMountingBlock;
+
 /**
  * Allows hooking into UIManager internals. This can be used to execute code at
  * specific points during the view updating process.
@@ -43,6 +45,13 @@
  */
 - (void)uiManagerWillPerformMounting:(RCTUIManager *)manager;
 
+/**
+ * Called right before flushing UI blocks and allows to intercept the mounting process.
+ * Return `YES` to cancel default execution of the `block` (and perform the
+ * execution later).
+ */
+- (BOOL)uiManager:(RCTUIManager *)manager performMountingWithBlock:(RCTUIManagerMountingBlock)block;
+
 /**
  * Called just after flushing UI blocks.
  * This is called from the UIManager queue.
diff --git a/React/Modules/RCTUIManagerObserverCoordinator.mm b/React/Modules/RCTUIManagerObserverCoordinator.mm
index 90e0255c9..a8fa5f6db 100644
--- a/React/Modules/RCTUIManagerObserverCoordinator.mm
+++ b/React/Modules/RCTUIManagerObserverCoordinator.mm
@@ -72,6 +72,20 @@
   }
 }
 
+- (BOOL)uiManager:(RCTUIManager *)manager performMountingWithBlock:(RCTUIManagerMountingBlock)block
+{
+  std::lock_guard<std::mutex> lock(_mutex);
+
+  for (id<RCTUIManagerObserver> observer in _observers) {
+    if ([observer respondsToSelector:@selector(uiManager:performMountingWithBlock:)]) {
+      if ([observer uiManager:manager performMountingWithBlock:block]) {
+        return YES;
+      }
+    }
+  }
+  return NO;
+}
+
 - (void)uiManagerDidPerformMounting:(RCTUIManager *)manager
 {
   std::lock_guard<std::mutex> lock(_mutex);