Use KVO to automatically respond correctly to changes in the extensionView size

TLYShyNavBar/TLYShyNavBarManager.m

@@ -19,6 +19,13 @@
 
 #import <objc/runtime.h>
 
+/* _scrollViewIsSuffecientlyLong attempts to determine if the expansionView can be shown by virtue of 
+ * excess space available in the scrollview relative to its content view. However, it breaks at edge cases,
+ * including if the content is just a bit more than threshold and then the user scrolls down further via
+ * the elastic scrollview... the logic suddenly thinks enough space is available and leads to the extention
+ * expanding. 
+ */
+//#define USE_BROKEN_SCROLLVIEW_LENGTH_LOGIC
 
 static void * const kTLYShyNavBarManagerKVOContext = (void*)&kTLYShyNavBarManagerKVOContext;
 
@@ -113,6 +120,7 @@ - (void)dealloc
 
     [[NSNotificationCenter defaultCenter] removeObserver:self];
     [_scrollView removeObserver:self forKeyPath:@"contentSize" context:kTLYShyNavBarManagerKVOContext];
+    [_extensionView removeObserver:self forKeyPath:@"frame" context:kTLYShyNavBarManagerKVOContext];
 }
 
 #pragma mark - Properties
@@ -221,9 +229,14 @@ - (void)setStickyExtensionView:(BOOL)stickyExtensionView
 
 - (BOOL)_scrollViewIsSuffecientlyLong
 {
+#ifdef USE_BROKEN_SCROLLVIEW_LENGTH_LOGIC
     CGRect scrollFrame = UIEdgeInsetsInsetRect(self.scrollView.bounds, self.scrollView.contentInset);
     CGFloat scrollableAmount = self.scrollView.contentSize.height - CGRectGetHeight(scrollFrame);
+
     return (scrollableAmount > [self.extensionController calculateTotalHeightRecursively]);
+#else
+    return YES;
+#endif
 }
 
 - (BOOL)_shouldHandleScrolling
@@ -357,9 +370,21 @@ - (void)observeValueForKeyPath:(NSString *)keyPath
 {
     if (context == kTLYShyNavBarManagerKVOContext)
     {
-        if (self.isViewControllerVisible && ![self _scrollViewIsSuffecientlyLong])
-        {
-            [self.navBarController expand];
+        if (object == _scrollView) {
+            if (self.isViewControllerVisible && ![self _scrollViewIsSuffecientlyLong])
+            {
+                [self.navBarController expand];
+            }
+
+        } else if (object == _extensionView) {
+            self.extensionViewContainer.frame = _extensionView.frame;
+
+            /* Disable scroll handling temporarily while laying out views to avoid double-changing content
+             * offsets in _handleScrolling. */
+            BOOL wasDisabled = self.disable;
+            self.disable = YES;
+            [self layoutViews];
+            self.disable = wasDisabled;
         }
     }
     else
@@ -374,6 +399,7 @@ - (void)setExtensionView:(UIView *)view
 {
     if (view != _extensionView)
     {
+        [_extensionView removeObserver:self forKeyPath:@"frame" context:kTLYShyNavBarManagerKVOContext];
         [_extensionView removeFromSuperview];
         _extensionView = view;
 
@@ -386,12 +412,10 @@ - (void)setExtensionView:(UIView *)view
         [self.extensionViewContainer addSubview:view];
         self.extensionViewContainer.userInteractionEnabled = view.userInteractionEnabled;
 
-        /* Disable scroll handling temporarily while laying out views to avoid double-changing content
-         * offsets in _handleScrolling. */
-        BOOL wasDisabled = self.disable;
-        self.disable = YES;
-        [self layoutViews];
-        self.disable = wasDisabled;
+        // Update our extension container view and layout if _extensionView's bounds changes
+        [_extensionView addObserver:self forKeyPath:@"frame"
+                            options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial)
+                            context:kTLYShyNavBarManagerKVOContext];
     }
 }