Adjust keyboard avoiding behavior (#943)

* Adjust keyboard avoiding behavior

Stop adjusting `scrollView.contentOffset` and let the system natively scroll because of the `scrollView.contentInset` change

* Add CHANGELOG entry

CHANGELOG.md

@@ -1,3 +1,5 @@
+* Adjusts scroll view content offset behavior when focusing on a text field [#943](https://github.com/stripe/stripe-ios/pull/943)
+
 ## 13.0.1 2018-05-17
 * Fixes an issue in `STPRedirectContext` causing some redirecting sources to fail in livemode due to prematurely dismissing the `SFSafariViewController` during the initial redirects. [#937](https://github.com/stripe/stripe-ios/pull/937)
 

Stripe/UIViewController+Stripe_KeyboardAvoiding.m

@@ -78,10 +78,8 @@ - (void)doKeyboardChangeAnimationWithNewFrame:(CGRect)keyboardFrame {
     self.lastKeyboardFrame = keyboardFrame;
 
     if (self.managedScrollView) {
-
         UIScrollView *scrollView = self.managedScrollView;
         UIView *scrollViewSuperView = self.managedScrollView.superview;
-        UIView *lastResponder = self.lastResponder;
 
         UIEdgeInsets contentInsets = scrollView.contentInset;
         UIEdgeInsets scrollIndicatorInsets = scrollView.scrollIndicatorInsets;
@@ -96,28 +94,11 @@ - (void)doKeyboardChangeAnimationWithNewFrame:(CGRect)keyboardFrame {
         self.currentBottomInsetChange += bottomInsetDelta;
         scrollView.contentInset = contentInsets;
         scrollView.scrollIndicatorInsets = scrollIndicatorInsets;
-
-        if (!lastResponder || bottomIntersection.size.height <= 0) {
-            scrollView.contentOffset = CGPointMake(0, -scrollView.contentInset.top);
-        }
-        else {
-            // the keyboard is visible
-            CGRect responderFrame = [lastResponder convertRect:lastResponder.bounds toView:scrollView];
-            CGRect keyboardFrameInScrollViewCoords = [scrollView convertRect:keyboardFrame fromView:nil];
-            CGPoint offset = scrollView.contentOffset;
-
-            CGFloat topOfScreenOffset = CGRectGetMinY(responderFrame);
-            CGFloat topOfKeyboardOffset = CGRectGetMinY(responderFrame) - CGRectGetMinY(keyboardFrameInScrollViewCoords);
-            offset.y = ((topOfScreenOffset + topOfKeyboardOffset) / 2) - scrollView.contentInset.top;
-            offset.y = MAX(offset.y, -scrollView.contentInset.top);
-            scrollView.contentOffset = offset;
-        }
     }
 
     if (self.keyboardFrameBlock) {
         self.keyboardFrameBlock(keyboardFrame, self.lastResponder);
     }
-
 }
 
 @end