Implementing a Countdown Timer in Objective-c? - iphone

Question

I am new to iOS programming. I am working on words matching game. In this game I need to implement time counter which shows minutes and seconds. I want when my game is started my timer to start with 3 minutes. Now I want to decrease this timer in reverse direction with seconds. my code just work for seconds..here is my code:
secondsLeft--;
int seconds = (secondsLeft %3600) % 60;
Timerlbl.text = [NSString stringWithFormat:#"%02d",seconds];
if (seconds==0)
{
UIAlertView *pAlert = [[UIAlertView alloc]initWithTitle:#"Sorry!!"
message:#"TimeOver" delegate:self cancelButtonTitle:#"OK"
otherButtonTitles:#"Cancel",nil];
[pAlert show];
[pAlert release];
}
}
In Viewdidload i call it through timer..
countDown=[NSTimer scheduledTimerWithTimeInterval:5.0 target:self
selector:#selector(TimeOver) userInfo:nil repeats:YES];
pleas any one guide me how can i do it in both minutes and seconds.

Answer 1

You can do it like this(ARC Enabled):-
#interface ViewController()
{
UILabel *progress;
NSTimer *timer;
int currMinute;
int currSeconds;
}
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
progress=[[UILabel alloc] initWithFrame:CGRectMake(80, 15, 100, 50)];
progress.textColor=[UIColor redColor];
[progress setText:#"Time : 3:00"];
progress.backgroundColor=[UIColor clearColor];
[self.view addSubview:progress];
currMinute=3;
currSeconds=00;
// Do any additional setup after loading the view, typically from a nib.
}
-(void)start
{
timer=[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(timerFired) userInfo:nil repeats:YES];
}
-(void)timerFired
{
if((currMinute>0 || currSeconds>=0) && currMinute>=0)
{
if(currSeconds==0)
{
currMinute-=1;
currSeconds=59;
}
else if(currSeconds>0)
{
currSeconds-=1;
}
if(currMinute>-1)
[progress setText:[NSString stringWithFormat:#"%#%d%#%02d",#"Time : ",currMinute,#":",currSeconds]];
}
else
{
[timer invalidate];
}
}

Answer 2

I know this is old question, but I want to share my way to achieve this. We have method (timeIntervalSinceDate:) to calculate the interval and have fixed amount of seconds to count down. In my case 300 s.
UPDATE JULY, 2015 SWIFT
#IBAction func startTimer(sender: UIButton) {
sender.selected = !sender.selected;
//if selected fire timer, otherwise stop
if (sender.selected) {
self.timer = NSTimer.scheduledTimerWithTimeInterval(0.1, target: self, selector: Selector("updateTimer"), userInfo: nil, repeats: true);
self.startDate = NSDate();
} else {
self.stopTimer();
}
}
func stopTimer() {
self.timer.invalidate();
}
func updateTimer() {
// Create date from the elapsed time
var currentDate:NSDate = NSDate();
var timeInterval:NSTimeInterval = currentDate.timeIntervalSinceDate(self.startDate!);
//300 seconds count down
var timeIntervalCountDown = 300 - timeInterval;
var timerDate:NSDate = NSDate(timeIntervalSince1970: timeIntervalCountDown);
// Create a date formatter
var dateFormatter = NSDateFormatter();
dateFormatter.dateFormat = "mm:ss";
dateFormatter.timeZone = NSTimeZone(forSecondsFromGMT: 0);
// Format the elapsed time and set it to the label
var timeString = dateFormatter.stringFromDate(timerDate);
self.timerLabel?.text = timeString;
}
Working github swift sample project
Objective-C
- (void)updateTimer
{
// Create date from the elapsed time
NSDate *currentDate = [NSDate date];
NSTimeInterval timeInterval = [currentDate
timeIntervalSinceDate:self.startDate];
NSLog(#"time interval %f",timeInterval);
//300 seconds count down
NSTimeInterval timeIntervalCountDown = 300 - timeInterval;
NSDate *timerDate = [NSDate
dateWithTimeIntervalSince1970:timeIntervalCountDown];
// Create a date formatter
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"mm:ss"];
[dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
// Format the elapsed time and set it to the label
NSString *timeString = [dateFormatter stringFromDate:timerDate];
self.stopWatch.text = timeString;
}
- (void)stopTimer
{
[self.stopWatchTimer invalidate];
self.stopWatchTimer = nil;
[self updateTimer];
}
- (void)startTimer
{
if (self.stopWatchTimer) {
[self.stopWatchTimer invalidate];
self.stopWatchTimer = nil;
}
self.startDate = [NSDate date];
// Create the stop watch timer that fires every 100 ms
self.stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
target:self
selector:#selector(updateTimer)
userInfo:nil
repeats:YES];
}
UPDATE:
it is extremely expensive to create a NSDateFormatter each time you pass through updateTimer. Far better to create the NSDateFormatter outside the loop and reuse it. Credits: #siburb

Answer 3

In .h file
IBOutlet UILabel* lblTimer;
NSTimer* gameTimer;
In .m file
-(void)viewDidLoad
{
[super viewDidLoad];
[self createTimer];
}
- (void)createTimer
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
gameTimer = [[NSTimer timerWithTimeInterval:1.00 target:self selector:#selector(timerFired:) userInfo:nil repeats:YES] retain];
[[NSRunLoop currentRunLoop] addTimer:gameTimer forMode:NSDefaultRunLoopMode];
timeCount = 20;
[runLoop run];
[pool release];
}
- (void)timerFired:(NSTimer *)timer
{
if(timeCount == 0)
{
[self timerExpired];
}
else
{
timeCount--;
if(timeCount == 0) {
[timer invalidate];
[self timerExpired];
}
}
lblTimer.text = [NSString stringWithFormat:#"%02d:%02d",timeCount/60, timeCount % 60];
self.title = lblTimer.text;
}
Bind the above Label Outlet with Label in View.
It is working correctly with Me

Answer 4

Simple and less code in Objective-C,
in .h file create objects for Timer and totalSeconds
NSTimer *timer;
int totalSeconds;
.m file
//you can call this method where you want
[self startTimer];
-(void)startOtpTimer {
totalSeconds = 120;//your time
timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self
selector:#selector(updateCountDownTime) userInfo:nil repeats:YES];
}
-(void)updateCountDownTime {
[self populateLabelwithTime:totalSeconds];
if( totalSeconds != 0) {
totalSeconds -= 1;
} else {
[timer invalidate];//stop timer
self.timeLabel.text = #"";//after reach 0 you can set empty string
}
}
- (void)populateLabelwithTime:(int)seconds {
self.timeLabel.text = [NSString stringWithFormat:#"%02d", totalSeconds];
}

Answer 5

You can use NSTimer to achieve this.