Add RCTWeakProxy to properly deallocate RCTUIImageViewAnimated

Summary:
@public
CADisplayLink strongly holds onto its target, so you have to use a weak proxy object to pass the target into the CADisplayLink.

Previously we passed a weak-self point (i.e. weakSelf) but this did not have the intended effect, since the pointer to self would still be passed to CADisplayLink, and thus it would hold onto the RCTUIImageViewAnimated strongly.

So is weakSelf doing anything other than using self?
It is but it's very minor and not useful. In the case that the object got de-allocated between assigning self to weakSelf and creating the CADisplayLink, then we would pass a nil target. This is actually impossible though because we are running an instance method, so self is implicitly retained! So semantically it is something different but in practice it is the same as passing self through.

Notes:
* This system was added originally in #24822
* #25636 then "enabled" this system by deprecating existing approach

Reviewed By: fkgozali

Differential Revision: D16939869

fbshipit-source-id: 7a0e947896f23aa30ad074d1dcb4d4db7543e00a

Libraries/Image/RCTUIImageViewAnimated.h

@@ -6,6 +6,9 @@
  */
 
 #import <React/RCTAnimatedImage.h>
+#import <React/RCTDefines.h>
+
+RCT_EXTERN void RCTUIImageViewEnableWeakProxy(BOOL enabled);
 
 @interface RCTUIImageViewAnimated : UIImageView
 

Libraries/Image/RCTUIImageViewAnimated.m

@@ -6,10 +6,16 @@
  */
 
 #import <React/RCTUIImageViewAnimated.h>
+#import <React/RCTWeakProxy.h>
 
 #import <mach/mach.h>
 #import <objc/runtime.h>
 
+static BOOL weakProxyEnabled = YES;
+void RCTUIImageViewEnableWeakProxy(BOOL enabled) {
+  weakProxyEnabled = enabled;
+}
+
 static NSUInteger RCTDeviceTotalMemory() {
   return (NSUInteger)[[NSProcessInfo processInfo] physicalMemory];
 }
@@ -146,8 +152,9 @@ - (NSOperationQueue *)fetchQueue
 - (CADisplayLink *)displayLink
 {
   if (!_displayLink) {
-    __weak __typeof(self) weakSelf = self;
-    _displayLink = [CADisplayLink displayLinkWithTarget:weakSelf selector:@selector(displayDidRefresh:)];
+    __weak typeof(self) weakSelf = self;
+    id target = weakProxyEnabled ? [RCTWeakProxy weakProxyWithTarget:self] : weakSelf;
+    _displayLink = [CADisplayLink displayLinkWithTarget:target selector:@selector(displayDidRefresh:)];
     NSString *runLoopMode = [NSProcessInfo processInfo].activeProcessorCount > 1 ? NSRunLoopCommonModes : NSDefaultRunLoopMode;
     [_displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:runLoopMode];
   }

React/Base/RCTWeakProxy.h

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <Foundation/Foundation.h>
+
+@interface RCTWeakProxy : NSObject
+
+@property (nonatomic, weak, readonly) id target;
+
++ (instancetype)weakProxyWithTarget:(id)target;
+
+@end

React/Base/RCTWeakProxy.m

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "RCTWeakProxy.h"
+
+@implementation RCTWeakProxy
+
+- (instancetype)initWithTarget:(id)target
+{
+  if (self = [super init]) {
+    _target = target;
+  }
+  return self;
+}
+
++ (instancetype)weakProxyWithTarget:(id)target
+{
+  return [[RCTWeakProxy alloc] initWithTarget:target];
+}
+
+- (id)forwardingTargetForSelector:(SEL)aSelector
+{
+  return _target;
+}
+
+@end