emit Dimensions change enent when app goes split screen

Summary:
Fixes facebook#26830 by removing version gating around `RCTUserInterfaceStyleDidChangeNotification` sent by `RCTRootView` and observing that notif for `Dimensions` changes.

Also centralizes `RCTUserInterfaceStyleDidChangeNotification` constant definition in new `RCTConstants` file.

Changelog:
[iOS] [Fixed] - `Dimensions` module now updates on initial split screen

Reviewed By: sammy-SC

Differential Revision: D18931098

fbshipit-source-id: e9784be3f544f3b10360fbc2d6ad0324273b1a8f

Author: sahrens

React/Base/RCTConstants.h

@@ -0,0 +1,11 @@
+/*
+ * 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 <React/RCTDefines.h>
+
+RCT_EXTERN NSString *const RCTUserInterfaceStyleDidChangeNotification;
+RCT_EXTERN NSString *const RCTUserInterfaceStyleDidChangeNotificationTraitCollectionKey;

React/Base/RCTConstants.m

@@ -0,0 +1,11 @@
+/*
+ * 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 "RCTConstants.h"
+
+NSString *const RCTUserInterfaceStyleDidChangeNotification = @"RCTUserInterfaceStyleDidChangeNotification";
+NSString *const RCTUserInterfaceStyleDidChangeNotificationTraitCollectionKey = @"traitCollection";

React/Base/RCTRootView.m

@@ -14,6 +14,7 @@
 #import "RCTAssert.h"
 #import "RCTBridge.h"
 #import "RCTBridge+Private.h"
+#import "RCTConstants.h"
 #import "RCTEventDispatcher.h"
 #import "RCTKeyCommands.h"
 #import "RCTLog.h"
@@ -33,7 +34,6 @@
 #endif
 
 NSString *const RCTContentDidAppearNotification = @"RCTContentDidAppearNotification";
-static NSString *const RCTUserInterfaceStyleDidChangeNotification = @"RCTUserInterfaceStyleDidChangeNotification";
 
 @interface RCTUIManager (RCTRootView)
 
@@ -367,21 +367,16 @@ - (void)contentViewInvalidated
   [self showLoadingView];
 }
 
-#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && defined(__IPHONE_13_0) && \
-    __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_13_0
 - (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection
 {
   [super traitCollectionDidChange:previousTraitCollection];
 
-  if (@available(iOS 13.0, *)) {
-    if ([previousTraitCollection hasDifferentColorAppearanceComparedToTraitCollection:self.traitCollection]) {
-      [[NSNotificationCenter defaultCenter] postNotificationName:RCTUserInterfaceStyleDidChangeNotification
-                                                          object:self
-                                                        userInfo:@{@"traitCollection": self.traitCollection}];
-    }
-  }
+  [[NSNotificationCenter defaultCenter] postNotificationName:RCTUserInterfaceStyleDidChangeNotification
+                                                      object:self
+                                                    userInfo:@{
+                                                      RCTUserInterfaceStyleDidChangeNotificationTraitCollectionKey: self.traitCollection,
+                                                    }];
 }
-#endif
 
 - (void)dealloc
 {

React/Base/Surface/SurfaceHostingView/RCTSurfaceHostingView.mm

@@ -7,14 +7,13 @@
 
 #import "RCTSurfaceHostingView.h"
 
+#import "RCTConstants.h"
 #import "RCTDefines.h"
 #import "RCTSurface.h"
 #import "RCTSurfaceDelegate.h"
 #import "RCTSurfaceView.h"
 #import "RCTUtils.h"
 
-static NSString *const RCTUserInterfaceStyleDidChangeNotification = @"RCTUserInterfaceStyleDidChangeNotification";
-
 @interface RCTSurfaceHostingView ()
 
 @property (nonatomic, assign) BOOL isActivityIndicatorViewVisible;
@@ -208,21 +207,15 @@ - (void)setActivityIndicatorViewFactory:(RCTSurfaceHostingViewActivityIndicatorV
 
 #pragma mark - UITraitCollection updates
 
-#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && defined(__IPHONE_13_0) && \
-    __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_13_0
 - (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection
 {
   [super traitCollectionDidChange:previousTraitCollection];
-
-  if (@available(iOS 13.0, *)) {
-    if ([previousTraitCollection hasDifferentColorAppearanceComparedToTraitCollection:self.traitCollection]) {
-      [[NSNotificationCenter defaultCenter] postNotificationName:RCTUserInterfaceStyleDidChangeNotification
-                                                          object:self
-                                                        userInfo:@{@"traitCollection": self.traitCollection}];
-    }
-  }
+  [[NSNotificationCenter defaultCenter] postNotificationName:RCTUserInterfaceStyleDidChangeNotification
+                                                      object:self
+                                                    userInfo:@{
+                                                      RCTUserInterfaceStyleDidChangeNotificationTraitCollectionKey: self.traitCollection,
+                                                    }];
 }
-#endif
 
 #pragma mark - Private stuff
 

React/CoreModules/RCTAppearance.h

@@ -12,7 +12,5 @@
 
 RCT_EXTERN void RCTEnableAppearancePreference(BOOL enabled);
 
-NSString *const RCTUserInterfaceStyleDidChangeNotification = @"RCTUserInterfaceStyleDidChangeNotification";
-
 @interface RCTAppearance : RCTEventEmitter <RCTBridgeModule>
 @end

React/CoreModules/RCTAppearance.mm

@@ -8,6 +8,7 @@
 #import "RCTAppearance.h"
 
 #import <FBReactNativeSpec/FBReactNativeSpec.h>
+#import <React/RCTConstants.h>
 #import <React/RCTEventEmitter.h>
 
 #import "CoreModulesPlugins.h"
@@ -86,7 +87,7 @@ - (void)appearanceChanged:(NSNotification *)notification
   NSDictionary *userInfo = [notification userInfo];
   UITraitCollection *traitCollection = nil;
   if (userInfo) {
-    traitCollection = userInfo[@"traitCollection"];
+    traitCollection = userInfo[RCTUserInterfaceStyleDidChangeNotificationTraitCollectionKey];
   }
   NSString *newColorScheme = RCTColorSchemePreference(traitCollection);
   if (![_currentColorScheme isEqualToString:newColorScheme]) {

React/CoreModules/RCTDeviceInfo.mm

@@ -10,6 +10,7 @@
 #import <FBReactNativeSpec/FBReactNativeSpec.h>
 #import <React/RCTAccessibilityManager.h>
 #import <React/RCTAssert.h>
+#import <React/RCTConstants.h>
 #import <React/RCTEventDispatcher.h>
 #import <React/RCTUIUtils.h>
 #import <React/RCTUtils.h>
@@ -61,9 +62,15 @@ - (void)setBridge:(RCTBridge *)bridge
   _currentInterfaceDimensions = RCTExportedDimensions(_bridge);
 
   [[NSNotificationCenter defaultCenter] addObserver:self
-                                           selector:@selector(interfaceFrameDidChange)
-                                               name:UIApplicationDidBecomeActiveNotification
-                                             object:nil];
+                                            selector:@selector(interfaceFrameDidChange)
+                                                name:UIApplicationDidBecomeActiveNotification
+                                              object:nil];
+
+  [[NSNotificationCenter defaultCenter] addObserver:self
+                                            selector:@selector(interfaceFrameDidChange)
+                                                name:RCTUserInterfaceStyleDidChangeNotification
+                                              object:nil];
+
 #endif
 }