Objective C - Uninterrupted timer using Singleton - ios

Question

My app consists of 3 ViewControllers. ViewController1 consists of a few labels and buttons where the user tries to solve a problem and presses a button. The button takes them to ViewController 2, where they are shown their stats (accuracy, time, etc.). The app then automatically navigates the user back to the game after 2 seconds. This process goes on for 2 minutes. After the 2 minutes is up, I want the app to navigate to a ViewController 3 (Main Menu).
I'm trying to implement a timer that that keeps going even when switching between view controllers. I've implemented (with the help of stackoverflow) a singleton class that has a timer property. However, it's not functioning as required. I've tried printing out values(commented in the code) to see what's going on, but no luck.
Here's my code:
ApplicationManager.m
//
// ApplicationManager.m
#import <Foundation/Foundation.h>
#import "ApplicationManager.h"
#implementation ApplicationManager
static ApplicationManager* appMgr = nil;
+(ApplicationManager*)instance{
#synchronized ([ApplicationManager class]){
if (!appMgr) {
appMgr = [[self alloc]init];
}
return appMgr;
}
return nil;
}
+(id) alloc{
#synchronized([ApplicationManager class]){
NSAssert((appMgr == nil), #"Only one instance of singleton class may be instantiated");
appMgr = [super alloc];
return appMgr;
}
}
+(id) init{
if (!(self == [super init])) {
return nil;
}
return self;
}
#end
ApplicationManager.h
#interface ApplicationManager : NSObject
+(ApplicationManager*) instance;
#property(weak, nonatomic) NSTimer* timer;
#property(weak, nonatomic) NSDate* startDate;
#end
ViewController.m
#import "ViewController.h"
#import "ApplicationManager.h"
NSString* const MAXTRIALTIME = #"00:50.000"; //50 Seconds just for testing purposes
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[[ApplicationManager instance]setstartDate:[NSDate date]];
[self startTimer];
//other functionalities
}
-(void)startTimer{
[[ApplicationManager instance] setTimer:[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(updateTimer) userInfo:nil repeats:YES]];
}
-(void) resetTimer{
[[[ApplicationManager instance] timer]invalidate];
}
-(void)updateTimer{
NSDate *currentTime = [NSDate date];
NSLog(#"Start Date2: %#", [[ApplicationManager instance]startDate]); //PRINTS (null)
NSTimeInterval timerInterval = [currentTime timeIntervalSinceDate:[[ApplicationManager instance]startDate]];
NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timerInterval];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
[dateFormatter setDateFormat:#"mm:ss.SSS"];
[dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
self.finalTime = [dateFormatter stringFromDate:timerDate];
NSLog(#"Time: %#\n",self.finalTime); //PRINTS random numbers
if ([self.finalTime isEqualToString:MAXTRIALTIME]) {
[self resetTimer];
//move to a different view controller
}
}
#end
ViewController.h
extern NSString* const MAXTRIALTIME;
#property (strong, nonatomic) NSString *finalTime;
//other declarations

Answer 1

In your ApplicationController singleton class you are making a call to self in the instance method. Any methods that instantiate a class (i.e. Methods that begin with a +) should never reference self as self will not exist at that point.
You need to do:
if (!appMgr) {
appMgr = [[ApplicationManager alloc] init];
}
This is the reason you are getting NULL when you print the startDate property.
Also, the ApplicationManager singleton is the owner of its timer property so that needs to be (strong). Weak properties are for references to objects that are owned by other classes. Check out ARC stuff.
Lastly the init method should be a - method not a + one and You don't need to override the alloc method as long as you only use the instance method to access your ApplicationManager. If I were you I'd get rid of the alloc and init methods altogether and just use the instance one.