add pinchEnabled prop to ScrollView

Summary:
When false, ScrollView disables use of pinch gestures to zoom in and out. This allows ScrollView's pinch gesture responder to be disabled to only allow zooming programmatically. The default value is ~false~ true.

**Test Plan**
Tested that pinch gesture responder is disabled when pinchEnabled=false.

/cc  nicklockwood sahrens

🍺
Closes https://github.com/facebook/react-native/pull/10037

Differential Revision: D5491953

Pulled By: shergin

fbshipit-source-id: eae16f92ec616e415b4ddacfccb84c697582daf9

Libraries/Components/ScrollView/ScrollView.js

@@ -271,6 +271,12 @@ const ScrollView = createReactClass({
      * Note: Vertical pagination is not supported on Android.
      */
     pagingEnabled: PropTypes.bool,
+    /**
+    * When true, ScrollView allows use of pinch gestures to zoom in and out.
+    * The default value is true.
+    * @platform ios
+    */
+    pinchGestureEnabled: PropTypes.bool,
     /**
      * When false, the view cannot be scrolled via touch interaction.
      * The default value is true.

React/Views/RCTScrollView.m

@@ -156,6 +156,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
 @property (nonatomic, assign) BOOL centerContent;
 #if !TARGET_OS_TV
 @property (nonatomic, strong) RCTRefreshControl *rctRefreshControl;
+@property (nonatomic, assign) BOOL pinchGestureEnabled;
 #endif
 
 @end
@@ -174,6 +175,10 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
       // scrollbar flip because we also flip it with whole `UIScrollView` flip.
       self.semanticContentAttribute = UISemanticContentAttributeForceLeftToRight;
     }
+
+    #if !TARGET_OS_TV
+    _pinchGestureEnabled = YES;
+    #endif
   }
   return self;
 }
@@ -330,6 +335,20 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init)
   _rctRefreshControl = refreshControl;
   [self addSubview:_rctRefreshControl];
 }
+
+- (void)setPinchGestureEnabled:(BOOL)pinchGestureEnabled
+{
+  self.pinchGestureRecognizer.enabled = pinchGestureEnabled;
+  _pinchGestureEnabled = pinchGestureEnabled;
+}
+
+- (void)didMoveToWindow
+{
+  [super didMoveToWindow];
+  // ScrollView enables pinch gesture late in its lifecycle. So simply setting it
+  // in the setter gets overriden when the view loads.
+  self.pinchGestureRecognizer.enabled = _pinchGestureEnabled;
+}
 #endif //TARGET_OS_TV
 
 @end

React/Views/RCTScrollViewManager.m

@@ -72,6 +72,7 @@ RCT_EXPORT_VIEW_PROPERTY(minimumZoomScale, CGFloat)
 RCT_EXPORT_VIEW_PROPERTY(scrollEnabled, BOOL)
 #if !TARGET_OS_TV
 RCT_EXPORT_VIEW_PROPERTY(pagingEnabled, BOOL)
+RCT_REMAP_VIEW_PROPERTY(pinchGestureEnabled, scrollView.pinchGestureEnabled, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(scrollsToTop, BOOL)
 #endif
 RCT_EXPORT_VIEW_PROPERTY(showsHorizontalScrollIndicator, BOOL)