Issue with integration into native iOS app

First of all, you can create a Unity view, but once it's started you cannot kill it (if you kill it you cannot reopen it again - this is where my app was crashing). So to go back to native, you have to hide the Unity view.

In my app specifically, I was integrating VR into a native app, so I had an intro scene that contained a button "Enter VR mode", which loaded the next scene. That being said, my quit was:

 public void QuitApp()
     {
         #if UNITY_EDITOR
         UnityEditor.EditorApplication.isPlaying = false;
         #endif
 
         #if UNITY_IOS && !UNITY_EDITOR
         LoadingScene.UnityPaused = true;
         SceneManager.LoadScene("LoadingScene");
         #endif
 
         #if UNITY_ANDROID && !UNITY_EDITOR
         AndroidJavaClass jc = new AndroidJavaClass ("com.unity3d.player.UnityPlayer");
         AndroidJavaObject jo = jc.GetStatic<AndroidJavaObject> ("currentActivity");
         jo.Call ("goBack");
         #endif
     }

Then in my Loading Scene I had:

     public static bool UnityPaused = false;
 
     #if UNITY_IOS && !UNITY_EDITOR
     [DllImport("__Internal")]
     private static extern void UnityRequestHide_MyPlugin();
     #endif
 
     void Start ()
     {
         #if UNITY_IOS && !UNITY_EDITOR
         if (LoadingScene.UnityPaused)
         {
             // if UnityPaused is true, Unity should go on background
             Debug.Log("Going back to native");
             UnityRequestHide_MyPlugin();
         }
         #endif
     }

In addition, inside Plugins/iOS, I added the following code (note, I didn't create a new plugin. Instead, I just added this method inside the existing CardboardAppController.mm that I already had imported with the GVR SDK. If you don't have any existing plugin or wish to create one, read the docs):

 void UnityRequestHide_MyPlugin() {
   if (GetAppController().quitHandler)
     GetAppController().quitHandler();
 }

If you followed the same tutorial for integration into native iOS, you'll have to make the following changes in the exported XCode project.

Inside UnityAppController.h, replace:

 inline UnityAppController* GetAppController()
 {
     return (UnityAppController*)[UIApplication sharedApplication].delegate;
 }

with:

 #import "AppDelegate.h"
 
 inline UnityAppController* GetAppController()
 {
     AppDelegate *delegate = (AppDelegate*)[UIApplication sharedApplication].delegate;
     return [delegate unityController];
 }

And inside UnityAppController.mm, find this method:

 - (BOOL)application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions

And add this at the beginning:

 _quitHandler = ^{
 [[NSNotificationCenter defaultCenter] postNotificationName:hideVR object:nil];
 };

I hope this helps/guides any one who's running into similar issues.