Making some code only run once

Question

I have some code that I would like to run only once in my MainViewController. It should run every time the user starts the app, but only after the MainViewController has loaded.

I don't want to run it in -(void)applicationDidFinishLaunching:(UIApplication *)application.

Here's the idea I had:

MainViewController.h

@interface IpadMainViewController : UIViewController <UISplitViewControllerDelegate> {     BOOL hasRun; }  @property (nonatomic, assign) BOOL hasRun; 

MainViewController.m

@synthesize hasRun;  -(void)viewDidLoad {     [super viewDidLoad];     if (hasRun == 0) {         // Do some stuff         hasRun = 1;     } } 

Any ideas?

Answer 1

Swift 1,2:

static var token: dispatch_once_t = 0  dispatch_once(&token) {   NSLog("Do it once") } 

Objective-C

static dispatch_once_t once; dispatch_once(&once, ^ {   NSLog(@"Do it once"); }); 

Swift 3,4:

dispatch_once is no longer available in Swift. In Swift, you can use lazily initialized globals or static properties and get the same thread-safety and called-once guarantees as dispatch_once provided Apple doc

let myGlobal = { … global contains initialization in a call to a closure … }() _ = myGlobal  // using myGlobal will invoke                // the initialization code only the first time it is used.