RCTUIManagerObserverCoordinator: new way to subscribe for granular notifications from UI Manager

Reviewed By: majak

Differential Revision: D4868591

fbshipit-source-id: 24a09ffa3e69dec5ce1f0a8715c7e4701d781996

React/Modules/RCTUIManager.h

@@ -59,24 +59,7 @@ RCT_EXTERN NSString *const RCTUIManagerDidRemoveRootViewNotification;
  */
 RCT_EXTERN NSString *const RCTUIManagerRootViewKey;
 
-@class RCTUIManager;
-
-/**
- * Allows to hook into UIManager internals. This can be used to execute code at
- * specific points during the view updating process.
- */
-@protocol RCTUIManagerObserver <NSObject>
-
-/**
- * Called before flushing UI blocks at the end of a batch. Note that this won't
- * get called for partial batches when using `unsafeFlushUIChangesBeforeBatchEnds`.
- * This is called from the UIManager queue. Can be used to add UI operations in that batch.
- */
-- (void)uiManagerWillFlushUIBlocks:(RCTUIManager *)manager;
-
-@end
-
-@protocol RCTScrollableProtocol;
+@class RCTUIManagerObserverCoordinator;
 
 /**
  * The RCTUIManager is the module responsible for updating the view hierarchy.
@@ -139,17 +122,6 @@ RCT_EXTERN NSString *const RCTUIManagerRootViewKey;
  */
 - (void)prependUIBlock:(RCTViewManagerUIBlock)block;
 
-/**
- * Add a UIManagerObserver. See the RCTUIManagerObserver protocol for more info. This
- * method can be called safely from any queue.
- */
-- (void)addUIManagerObserver:(id<RCTUIManagerObserver>)observer;
-
-/**
- * Remove a UIManagerObserver. This method can be called safely from any queue.
- */
-- (void)removeUIManagerObserver:(id<RCTUIManagerObserver>)observer;
-
 /**
  * Used by native animated module to bypass the process of updating the values through the shadow
  * view hierarchy. This method will directly update native views, which means that updates for
@@ -192,6 +164,12 @@ RCT_EXTERN NSString *const RCTUIManagerRootViewKey;
  */
 - (void)setNeedsLayout;
 
+/**
+ * Dedicated object for subscribing for UIManager events.
+ * See `RCTUIManagerObserver` protocol for more details.
+ */
+@property (atomic, retain, readonly) RCTUIManagerObserverCoordinator *observerCoordinator;
+
 @end
 
 @interface RCTUIManager (Deprecated)

React/Modules/RCTUIManager.m

@@ -33,6 +33,7 @@
 #import "RCTScrollableProtocol.h"
 #import "RCTShadowView.h"
 #import "RCTUtils.h"
+#import "RCTUIManagerObserverCoordinator.h"
 #import "RCTView.h"
 #import "RCTViewManager.h"
 #import "UIView+React.h"
@@ -225,7 +226,6 @@ static UIViewAnimationOptions UIViewAnimationOptionsFromRCTAnimationType(RCTAnim
   NSDictionary *_componentDataByName;
 
   NSMutableSet<id<RCTComponent>> *_bridgeTransactionListeners;
-  NSMutableSet<id<RCTUIManagerObserver>> *_uiManagerObservers;
 }
 
 @synthesize bridge = _bridge;
@@ -306,7 +306,7 @@ RCT_EXPORT_MODULE()
   _rootViewTags = [NSMutableSet new];
 
   _bridgeTransactionListeners = [NSMutableSet new];
-  _uiManagerObservers = [NSMutableSet new];
+  _observerCoordinator = [RCTUIManagerObserverCoordinator new];
 
   _viewsToBeDeleted = [NSMutableSet new];
 
@@ -723,20 +723,6 @@ BOOL RCTIsUIManagerQueue()
   }
 }
 
-- (void)addUIManagerObserver:(id<RCTUIManagerObserver>)observer
-{
-  dispatch_async(RCTGetUIManagerQueue(), ^{
-    [self->_uiManagerObservers addObject:observer];
-  });
-}
-
-- (void)removeUIManagerObserver:(id<RCTUIManagerObserver>)observer
-{
-  dispatch_async(RCTGetUIManagerQueue(), ^{
-    [self->_uiManagerObservers removeObject:observer];
-  });
-}
-
 /**
  * A method to be called from JS, which takes a container ID and then releases
  * all subviews for that container upon receipt.
@@ -1159,10 +1145,19 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
     [self addUIBlock:uiBlock];
   }
 
+  [_observerCoordinator uiManagerWillPerformLayout:self];
+
   // Perform layout
   for (NSNumber *reactTag in _rootViewTags) {
     RCTRootShadowView *rootView = (RCTRootShadowView *)_shadowViewRegistry[reactTag];
     [self addUIBlock:[self uiBlockWithLayoutUpdateForRootView:rootView]];
+  }
+
+  [_observerCoordinator uiManagerDidPerformLayout:self];
+
+  // Properies propagation
+  for (NSNumber *reactTag in _rootViewTags) {
+    RCTRootShadowView *rootView = (RCTRootShadowView *)_shadowViewRegistry[reactTag];
     [self _amendPendingUIBlocksWithStylePropagationUpdateForShadowView:rootView];
   }
 
@@ -1175,9 +1170,7 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
     }
   }];
 
-  for (id<RCTUIManagerObserver> observer in _uiManagerObservers) {
-    [observer uiManagerWillFlushUIBlocks:self];
-  }
+  [_observerCoordinator uiManagerWillFlushUIBlocks:self];
 
   [self flushUIBlocks];
 }

React/Modules/RCTUIManagerObserverCoordinator.h

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import <UIKit/UIKit.h>
+
+#import <React/RCTViewManager.h>
+
+/**
+ * Allows to hook into UIManager internals. This can be used to execute code at
+ * specific points during the view updating process.
+ * All observer handler is called on UIManager queue.
+ */
+@protocol RCTUIManagerObserver <NSObject>
+
+@optional
+
+/**
+ * Called just before the UIManager layout views.
+ * It allows performing some operation for components which contain custom
+ * layout logic right before regular Yoga based layout. So, for instance,
+ * some components which have own React-independent state can compute and cache
+ * own intrinsic content size (which will be used by Yoga) at this point.
+ */
+- (void)uiManagerWillPerformLayout:(RCTUIManager *)manager;
+
+/**
+ * Called just after the UIManager layout views.
+ * It allows performing custom layout logic right after regular Yoga based layout.
+ * So, for instance, this can be used for computing final layout for a component,
+ * since it has its final frame set by Yoga at this point.
+ */
+- (void)uiManagerDidPerformLayout:(RCTUIManager *)manager;
+
+/**
+ * Called before flushing UI blocks at the end of a batch. Note that this won't
+ * get called for partial batches when using `unsafeFlushUIChangesBeforeBatchEnds`.
+ * This is called from the UIManager queue. Can be used to add UI operations in that batch.
+ */
+- (void)uiManagerWillFlushUIBlocks:(RCTUIManager *)manager;
+
+@end
+
+/**
+ * Simple helper which take care of RCTUIManager's observers.
+ */
+@interface RCTUIManagerObserverCoordinator : NSObject <RCTUIManagerObserver>
+
+/**
+ * Add a UIManagerObserver. See the `RCTUIManagerObserver` protocol for more info.
+ * References to observers are held weakly.
+ * This method can be called safely from any queue.
+ */
+- (void)addObserver:(id<RCTUIManagerObserver>)observer;
+
+/**
+ * Remove a `UIManagerObserver`.
+ * This method can be called safely from any queue.
+ */
+- (void)removeObserver:(id<RCTUIManagerObserver>)observer;
+
+@end

React/Modules/RCTUIManagerObserverCoordinator.m

@@ -0,0 +1,70 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import "RCTUIManagerObserverCoordinator.h"
+
+#import "RCTUIManager.h"
+
+@implementation RCTUIManagerObserverCoordinator {
+  NSHashTable<id<RCTUIManagerObserver>> *_observers;
+}
+
+- (instancetype)init
+{
+  if (self = [super init]) {
+    _observers = [[NSHashTable alloc] initWithOptions:NSHashTableWeakMemory capacity:0];
+  }
+
+  return self;
+}
+
+- (void)addObserver:(id<RCTUIManagerObserver>)observer
+{
+  dispatch_async(RCTGetUIManagerQueue(), ^{
+    [self->_observers addObject:observer];
+  });
+}
+
+- (void)removeObserver:(id<RCTUIManagerObserver>)observer
+{
+  dispatch_async(RCTGetUIManagerQueue(), ^{
+    [self->_observers removeObject:observer];
+  });
+}
+
+#pragma mark - RCTUIManagerObserver
+
+- (void)uiManagerWillPerformLayout:(RCTUIManager *)manager
+{
+  for (id<RCTUIManagerObserver> observer in _observers) {
+    if ([observer respondsToSelector:@selector(uiManagerWillPerformLayout:)]) {
+      [observer uiManagerWillPerformLayout:manager];
+    }
+  }
+}
+
+- (void)uiManagerDidPerformLayout:(RCTUIManager *)manager
+{
+  for (id<RCTUIManagerObserver> observer in _observers) {
+    if ([observer respondsToSelector:@selector(uiManagerDidPerformLayout:)]) {
+      [observer uiManagerDidPerformLayout:manager];
+    }
+  }
+}
+
+- (void)uiManagerWillFlushUIBlocks:(RCTUIManager *)manager
+{
+  for (id<RCTUIManagerObserver> observer in _observers) {
+    if ([observer respondsToSelector:@selector(uiManagerWillFlushUIBlocks:)]) {
+      [observer uiManagerWillFlushUIBlocks:manager];
+    }
+  }
+}
+
+@end