How can I prevent ViewControllers from being deallocated after I inject them with a dependency in application:DidFinishLaunchingWithOptions:

Question

I am trying to inject a dependency (to a data store) into all the viewControllers in my tabbed app, from AppDelegate, rather than access the datastore by reaching back into the appDelegate. I am using a storyboard.

I do this in application:didFinishLaunchingWithOptions:, and the code executes without errors.

However, when any of the viewControllers is presented, the property into which I have injected the datastore contains nil. I was expecting it to have a reference to the datastore.

I thought maybe my datastore went out of scope after application:didFinishLaunchingWithOptions returns and caused the datastore to become nil. But to my knowledge ARC should prevent that.

I started to suspect that maybe the VCs might go out of existence after application:didFinishLaunchingWithOptions: finishes running. So I added a dealloc method to the view controllers to see if it gets called, and lo-and-behold, it did. That explains why the dependency I injected previously is no longer there.

Now I am stuck, as I don't know how else to inject the dependency into the view controllers. The only idea I have left is to add properties to my AppDelegate and use them to retain the view controllers, but that feels a bit dangerous cause I'm now interfering with iOS management of view controllers.

Here is the code in AppDelegate:

//AppDelegate.h
#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@end

//AppDelegate.m
#import "AppDelegate.h"
#import "InjectedViewController.h"
#import "InjectedDataStore.h"
@interface AppDelegate ()
@property (strong, nonatomic) InjectedDataStore *myDataStore;
@end

@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.

UIStoryboard *storyBoard;
storyBoard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
UIViewController *initViewController = [storyBoard instantiateInitialViewController];
[self.window setRootViewController:initViewController];


if (!_myDataStore) {
    self.myDataStore = [[InjectedDataStore alloc]init];
    NSLog(@"alloc inited %@", self.myDataStore);
}

UITabBarController *tabBarController = (UITabBarController *)initViewController;
    for (InjectedViewController *ivc in tabBarController.viewControllers) {
        ivc.dataStore = self.myDataStore;
        NSLog(@"dataStore injected into ivc: %@", ivc.dataStore);
    }

NSLog(@"application:didFinishLaunching... done");

return YES;
}

@end

here is my view controller subclass with the property into which I want to inject:

//InjectedViewController.h

#import <UIKit/UIKit.h>
#import "InjectedDataStore.h"

NS_ASSUME_NONNULL_BEGIN

@interface InjectedViewController : UIViewController
@property (strong, nonatomic) InjectedDataStore *dataStore;
@end

NS_ASSUME_NONNULL_END

InjectedViewController.m is boilerplate and otherwise empty. InjectedDataStore.m and .h are a boilerplate Cocoa Touch class without any properties or methods.

and here is one of the viewcontrollers - it is embedded in a tab view. (The other view controller for the other tab is identical.

//FirstViewController.h
#import <UIKit/UIKit.h> 
#import "InjectedViewController.h"
@interface FirstViewController : InjectedViewController
@end

//FirstViewController.m
#import "FirstViewController.h"

@interface FirstViewController ()

@end

@implementation FirstViewController

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
NSLog(@"data store for FirstVC: %@", self.dataStore);
}

- (void) dealloc {
NSLog(@"First VC dealloc called");
}
@end

and finally, the console output:

alloc inited <InjectedDataStore: 0x600001d483a0> 
dataStore injected into ivc: <InjectedDataStore: 0x600001d483a0> 
dataStore injected into ivc: <InjectedDataStore: 0x600001d483a0>
application:didFinishLaunching... done

First VC dealloc called   ///this is what causes the injected element to disappear.
Second VC dealloc called  ///causes the injected element to disappear.

data store for FirstVC: (null) 
data store for SecondVC: (null)

(I would eventually implement a protocol, but for now since I am stuck at getting the injection to work I have left that out.)

It seems to me what I have done here is very similar to @juanignaciosi 's answer to this question:

Appreciate any feedback, I am a relative newbie to iOS.

Answer 1

Your's window property is nil. Since iOS 13 system is using window property from scene delegate. Just remove scene delegate and UIApplicationSceneManifest from plist if you don't need it.