fix push while transitioning (#983)

ios/RCCNavigationController.m

 #import "UIViewController+Rotation.h"
 
 @implementation RCCNavigationController
+{
+  BOOL _transitioning;
+  NSMutableArray *_queuedViewControllers;
+}
 
 NSString const *CALLBACK_ASSOCIATED_KEY = @"RCCNavigationController.CALLBACK_ASSOCIATED_KEY";
 NSString const *CALLBACK_ASSOCIATED_ID = @"RCCNavigationController.CALLBACK_ASSOCIATED_ID";
 
 - (instancetype)initWithProps:(NSDictionary *)props children:(NSArray *)children globalProps:(NSDictionary*)globalProps bridge:(RCTBridge *)bridge
 {
+  _queuedViewControllers = [NSMutableArray new];
+  
   NSString *component = props[@"component"];
   if (!component) return nil;
   
     [topViewController setNavBarVisibilityChange:animatedBool];
     
   }
+  
+  // setStyle
+  if ([performAction isEqualToString:@"setStyle"])
+  {
+    
+    NSDictionary *navigatorStyle = actionParams;
     
-    // setStyle
-    if ([performAction isEqualToString:@"setStyle"])
+    // merge the navigatorStyle of our parent
+    if ([self.topViewController isKindOfClass:[RCCViewController class]])
     {
-        
-        NSDictionary *navigatorStyle = actionParams;
-        
-        // merge the navigatorStyle of our parent
-        if ([self.topViewController isKindOfClass:[RCCViewController class]])
-        {
-            RCCViewController *parent = (RCCViewController*)self.topViewController;
-            NSMutableDictionary *mergedStyle = [NSMutableDictionary dictionaryWithDictionary:parent.navigatorStyle];
-            
-            // there are a few styles that we don't want to remember from our parent (they should be local)
-            [mergedStyle setValuesForKeysWithDictionary:navigatorStyle];
-            navigatorStyle = mergedStyle;
-            
-            parent.navigatorStyle = navigatorStyle;
-            
-            [parent setStyleOnInit];
-            [parent updateStyle];
-        }
+      RCCViewController *parent = (RCCViewController*)self.topViewController;
+      NSMutableDictionary *mergedStyle = [NSMutableDictionary dictionaryWithDictionary:parent.navigatorStyle];
+      
+      // there are a few styles that we don't want to remember from our parent (they should be local)
+      [mergedStyle setValuesForKeysWithDictionary:navigatorStyle];
+      navigatorStyle = mergedStyle;
+      
+      parent.navigatorStyle = navigatorStyle;
+      
+      [parent setStyleOnInit];
+      [parent updateStyle];
     }
+  }
 }
 
 -(void)onButtonPress:(UIBarButtonItem*)barButtonItem
   return [self.topViewController preferredStatusBarStyle];
 }
 
+- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated
+{
+  if(_transitioning)
+  {
+    NSDictionary *pushDetails =@{ @"viewController": viewController, @"animated": @(animated) };
+    [_queuedViewControllers addObject:pushDetails];
+    
+    return;
+  }
+  
+  _transitioning = YES;
+  
+  [super pushViewController:viewController animated:animated];
+}
+
 
 #pragma mark - UINavigationControllerDelegate
 
   [viewController setNeedsStatusBarAppearanceUpdate];
 }
 
+- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated
+{
+  dispatch_async(dispatch_get_main_queue(), ^{
+    _transitioning = NO;
+    if ([_queuedViewControllers count] > 0) {
+      NSDictionary *toPushDetails = [_queuedViewControllers firstObject];
+      [_queuedViewControllers removeObjectAtIndex:0];
+      [self pushViewController:toPushDetails[@"viewController"] animated:[toPushDetails[@"animated"] boolValue]];
+    }
+  });
+}
+
 
 @end