-[RCTUIManagerObserver uiManagerDidPerformMounting]

Reviewed By: rsnara

Differential Revision: D6434461

fbshipit-source-id: a66407936cec3582cb27c57eb8e36dc225149c45

React/Modules/RCTUIManager.m

@@ -431,7 +431,7 @@ static NSDictionary *deviceOrientationEventBody(UIDeviceOrientation orientation)
 
     shadowView.backgroundColor = color;
     [self _amendPendingUIBlocksWithStylePropagationUpdateForShadowView:shadowView];
-    [self flushUIBlocks];
+    [self flushUIBlocksWithCompletion:^{}];
   } forTag:view.reactTag];
 }
 
@@ -1128,10 +1128,12 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
 
   [_observerCoordinator uiManagerWillPerformMounting:self];
 
-  [self flushUIBlocks];
+  [self flushUIBlocksWithCompletion:^{
+    [self->_observerCoordinator uiManagerDidPerformMounting:self];
+  }];
 }
 
-- (void)flushUIBlocks
+- (void)flushUIBlocksWithCompletion:(void (^)(void))completion;
 {
   RCTAssertUIManagerQueue();
 
@@ -1141,7 +1143,11 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
   NSArray<RCTViewManagerUIBlock> *previousPendingUIBlocks = _pendingUIBlocks;
   _pendingUIBlocks = [NSMutableArray new];
 
-  if (previousPendingUIBlocks.count) {
+  if (previousPendingUIBlocks.count == 0) {
+    completion();
+    return;
+  }
+
   // Execute the previously queued UI blocks
   RCTProfileBeginFlowEvent();
   RCTExecuteOnMainQueue(^{
@@ -1158,9 +1164,10 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
       RCTLogError(@"Exception thrown while executing UI block: %@", exception);
     }
     RCT_PROFILE_END_EVENT(RCTProfileTagAlways, @"");
+
+    RCTExecuteOnUIManagerQueue(completion);
   });
 }
-}
 
 - (void)setNeedsLayout
 {

React/Modules/RCTUIManagerObserverCoordinator.h

@@ -45,6 +45,12 @@
  */
 - (void)uiManagerWillPerformMounting:(RCTUIManager *)manager;
 
+/**
+ * Called just after flushing UI blocks.
+ * This is called from the UIManager queue.
+ */
+- (void)uiManagerDidPerformMounting:(RCTUIManager *)manager;
+
 @end
 
 /**

React/Modules/RCTUIManagerObserverCoordinator.mm

@@ -74,4 +74,16 @@
   }
 }
 
+- (void)uiManagerDidPerformMounting:(RCTUIManager *)manager
+{
+  std::lock_guard<std::mutex> lock(_mutex);
+
+  for (id<RCTUIManagerObserver> observer in _observers) {
+    if ([observer respondsToSelector:@selector(uiManagerDidPerformMounting:)]) {
+      [observer uiManagerDidPerformMounting:manager];
+    }
+  }
+}
+
+
 @end