Nav ios hide hairline

Summary:
For the current project I am working on I needed to add a boolean option (`shadowHidden`) to remove the 1px hairline shadow from the NavigationIOS component:

`<NavigatorIOS shadowHidden={true} initialRoute={...} />`

By default, or with `shadowHidden={false}` it looks like this:

![withhairline](https://cloud.githubusercontent.com/assets/129330/8145401/d2704956-11d4-11e5-86e8-a75435b68480.png)
Setting the shadow hidden  with `shadowHidden={true}` looks like this:

![nohairline2](https://cloud.githubusercontent.com/assets/129330/8145405/148ed56e-11d5-11e5-85d6-f8cd3453d5ac.png)

The code it uses to do the actual hiding is... a bit of a hack (*I* think), but it's the only way currently to do it, and is the way they do it in the iPhone calendar app: iterating through the subviews and removing the shadow image.

This removes the shadow *and* keeps the translucent blurry effect with a ScrollView (see this [SO discussion](http://stackoverflow.com/questions/18160173/how-to-remove-uinavigationbar-inner
Closes https://github.com/facebook/react-native/pull/1615
Github Author: Mr Speaker <mrspeaker@gmail.com>

Libraries/Components/Navigation/NavigatorIOS.ios.js

@@ -60,6 +60,7 @@ var RCTNavigatorItem = createReactNativeComponentClass({
     tintColor: true,
     translucent: true,
     navigationBarHidden: true,
+    shadowHidden: true,
     titleTextColor: true,
     style: true,
   },
@@ -281,6 +282,11 @@ var NavigatorIOS = React.createClass({
      */
     navigationBarHidden: PropTypes.bool,
 
+    /**
+     * A Boolean value that indicates whether to hide the 1px hairline shadow
+     */
+    shadowHidden: PropTypes.bool,
+
     /**
      * The default wrapper style for components in the navigator.
      * A common use case is to set the backgroundColor for every page
@@ -640,6 +646,7 @@ var NavigatorIOS = React.createClass({
           rightButtonTitle={route.rightButtonTitle}
           onNavRightButtonTap={route.onRightButtonPress}
           navigationBarHidden={this.props.navigationBarHidden}
+          shadowHidden={this.props.shadowHidden}
           tintColor={this.props.tintColor}
           barTintColor={this.props.barTintColor}
           translucent={this.props.translucent !== false}

React/Views/RCTNavItem.h

@@ -19,6 +19,7 @@
 @property (nonatomic, strong) UIImage *backButtonIcon;
 @property (nonatomic, copy) NSString *backButtonTitle;
 @property (nonatomic, assign) BOOL navigationBarHidden;
+@property (nonatomic, assign) BOOL shadowHidden;
 @property (nonatomic, strong) UIColor *tintColor;
 @property (nonatomic, strong) UIColor *barTintColor;
 @property (nonatomic, strong) UIColor *titleTextColor;

React/Views/RCTNavItemManager.m

@@ -22,6 +22,7 @@ RCT_EXPORT_MODULE()
 }
 
 RCT_EXPORT_VIEW_PROPERTY(navigationBarHidden, BOOL)
+RCT_EXPORT_VIEW_PROPERTY(shadowHidden, BOOL)
 RCT_EXPORT_VIEW_PROPERTY(tintColor, UIColor)
 RCT_EXPORT_VIEW_PROPERTY(barTintColor, UIColor)
 RCT_EXPORT_VIEW_PROPERTY(translucent, BOOL)

React/Views/RCTWrapperViewController.m

@@ -63,6 +63,20 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
   _currentBottomLayoutGuide = self.bottomLayoutGuide;
 }
 
+static UIView *RCTFindNavBarShadowViewInView(UIView *view)
+{
+  if ([view isKindOfClass:[UIImageView class]] && view.bounds.size.height <= 1) {
+    return view;
+  }
+  for (UIView *subview in view.subviews) {
+    UIView *shadowView = RCTFindNavBarShadowViewInView(subview);
+    if (shadowView) {
+      return shadowView;
+    }
+  }
+  return nil;
+}
+
 - (void)viewWillAppear:(BOOL)animated
 {
   [super viewWillAppear:animated];
@@ -71,20 +85,18 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
   if ([self.parentViewController isKindOfClass:[UINavigationController class]])
   {
     [self.navigationController
-      setNavigationBarHidden:_navItem.navigationBarHidden
-      animated:animated];
-
-    if (!_navItem) {
-      return;
-    }
+     setNavigationBarHidden:_navItem.navigationBarHidden
+     animated:animated];
 
     UINavigationBar *bar = self.navigationController.navigationBar;
     bar.barTintColor = _navItem.barTintColor;
     bar.tintColor = _navItem.tintColor;
     bar.translucent = _navItem.translucent;
-    if (_navItem.titleTextColor) {
-      [bar setTitleTextAttributes:@{NSForegroundColorAttributeName : _navItem.titleTextColor}];
-    }
+    bar.titleTextAttributes = _navItem.titleTextColor ? @{
+      NSForegroundColorAttributeName: _navItem.titleTextColor
+    } : nil;
+
+    RCTFindNavBarShadowViewInView(bar).hidden = _navItem.shadowHidden;
 
     UINavigationItem *item = self.navigationItem;
     item.title = _navItem.title;
@@ -129,7 +141,8 @@ RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
   // finishes, be it a swipe to go back or a standard tap on the back button
   [super didMoveToParentViewController:parent];
   if (parent == nil || [parent isKindOfClass:[UINavigationController class]]) {
-    [self.navigationListener wrapperViewController:self didMoveToNavigationController:(UINavigationController *)parent];
+    [self.navigationListener wrapperViewController:self
+                     didMoveToNavigationController:(UINavigationController *)parent];
   }
 }