fix(ios): update pager view only when layout changed (#462)

Currently we update the pager view in `layoutSubviews` method to make sure that our layout stays in sync. However, this method seems to get called even if the layout didn't change - and calling `updateDataSource` dismisses the keyboard if it's visible, This causes the keyboard to be dismissed when it's not supposed to - e.g. auto focus on input doesn't work, keyboard doesn't stay open when app goes to background etc.

This adds a check to make sure that we call `updateDataSourcez only if the layout changes, which avoids unnecessary updates and avoids dismissing the keyboard unnecessarily.

Fixes #441

Author: satya164

ios/ReactNativePageView.h

@@ -23,6 +23,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property(nonatomic, copy) RCTDirectEventBlock onPageScrollStateChanged;
 @property(nonatomic) BOOL overdrag;
 @property(nonatomic) NSString* layoutDirection;
+@property(nonatomic) CGRect previousBounds;
 
 
 - (void)goTo:(NSInteger)index animated:(BOOL)animated;

ios/ReactNativePageView.m

@@ -47,6 +47,7 @@ - (instancetype)initWithEventDispatcher:(RCTEventDispatcher *)eventDispatcher {
         _cachedControllers = [NSHashTable weakObjectsHashTable];
         _overdrag = NO;
         _layoutDirection = @"ltr";
+        _previousBounds = CGRectMake(0, 0, 0, 0);
     }
     return self;
 }
@@ -55,8 +56,13 @@ - (void)layoutSubviews {
     [super layoutSubviews];
     if (self.reactPageViewController) {
         [self shouldScroll:self.scrollEnabled];
-        //Below line fix bug, where the view does not update after orientation changed.
-        [self updateDataSource];
+
+        if (!CGRectEqualToRect(self.previousBounds, CGRectMake(0, 0, 0, 0)) && !CGRectEqualToRect(self.bounds, self.previousBounds)) {
+            // Below line fix bug, where the view does not update after orientation changed.
+            [self updateDataSource];
+        }
+
+        self.previousBounds = CGRectMake(self.bounds.origin.x, self.bounds.origin.y, self.bounds.size.width, self.bounds.size.height);
     }
 }