I am trying to create an NSTimer that counts up from 00:00:00 to whenever the user presses stop. I have created an NSDateInterval of 1 second, but I can't get it to count up from 00:00:00, only the current date or a date that I set.
What is the best way to do this? And is NSTimer the best way to do this or should I just get the difference between the time the user presses the first button ([NSDate date] to set it) and the time at that second (a selector fired off by NSTimer)? I want to make sure there is as little accuracy fault as possible, and I am aware of NSTimer's problems with accuracy sometimes.
Save the time the timer starts with [NSDate date], and then record the time it stops as well. The display time will be the difference, displayed as you listed. The NSTimer will be used just to trigger an update, and you can set the interval fairly small, say 1/10th of a second. Something like:
[NSTimer scheduledTimerWithTimeInterval: 0.1f target: self
selector: #selector(updateTimeDisplay) userInfo: nil repeats: YES];
Related
I am trying to use NSTimer to create a Stop-watch style timer that increments every 0.1 seconds, but it seems to be running too fast sometimes ..
This is how I've done it:
Timer =[NSTimer scheduledTimerWithTimeInterval: 0.1 target:self selector:#selector(updateTimeLabel) userInfo:nil repeats: YES];
and then:
-(void)updateTimeLabel
{
maxTime=maxTime+0.1;
timerLabel.text =[NSString stringWithFormat:#"%.1f Seconds",maxTime];
}
This will display the value of the timer in the Label, and I can later utilize maxTime as the time when the Timer is stopped ...
THe problem is that it runs very inaccurately.
Is there a method where I can make sure that NSTimer fires strictly every 0.1 seconds accurately ? I know that NSTimer isn't accurate , and I'm asking for a tweak to make it accurate.
THanks
According to the NSTimer documentation, it is not meant to be accurate.
Because of the various input sources a typical run loop manages, the effective resolution of the time interval for a timer is limited to on the order of 50-100 milliseconds. If a timer’s firing time occurs during a long callout or while the run loop is in a mode that is not monitoring the timer, the timer does not fire until the next time the run loop checks the timer. Therefore, the actual time at which the timer fires potentially can be a significant period of time after the scheduled firing time.
You may want to use the dispatch_after function from GCD, which is suggested by the official documentation for this exact purpose (creating a timer).
If you want to perform a block once after a specified time interval, you can use the dispatch_after or dispatch_after_f function.
By the way, I agree with Caleb's answer. You probably are going to solve your problems if you don't accumulate error like your doing right now.
If you store the start date and recalculate the time at every iteration using the -timeIntervalSince: method, you're gonna end up with an accurate UI update, regardless of the timer precision.
Here's a class you can use to do what you want:
#interface StopWatch()
#property ( nonatomic, strong ) NSTimer * displayTimer ;
#property ( nonatomic ) CFAbsoluteTime startTime ;
#end
#implementation StopWatch
-(void)dealloc
{
[ self.displayTimer invalidate ] ;
}
-(void)startTimer
{
self.startTime = CFAbsoluteTimeGetCurrent() ;
self.displayTimer = [ NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:#selector( timerFired: ) userInfo:nil repeats:YES ] ;
}
-(void)stopTimer
{
[ self.displayTimer invalidate ] ;
self.displayTimer = nil ;
CFAbsoluteTime elapsedTime = CFAbsoluteTimeGetCurrent() - self.startTime ;
[ self updateDisplay:elapsedTime ] ;
}
-(void)timerFired:(NSTimer*)timer
{
CFAbsoluteTime elapsedTime = CFAbsoluteTimeGetCurrent() - self.startTime ;
[ self updateDisplay:elapsedTime ] ;
}
-(void)updateDisplay:(CFAbsoluteTime)elapsedTime
{
// update your label here
}
#end
The key points are:
do your timing by saving the system time when the stop watch is started into a variable.
when the the stop watch is stopped, calculate the elapsed time by subtracting the stop watch start time from the current time
update your display using your timer. It doesn't matter if your timer is accurate or not for this. If you are trying to guarantee display updates at least every 0.1s, you can try setting your timer interval to 1/2 the minimum update time (0.05s).
maxTime=maxTime+0.1;
This is the wrong way to go. You don't want to use a timer to accumulate the elapsed time because you'll be accumulating error along with it. Use the timer to periodically trigger a method that calculates the elapsed time using NSDate, and then updates the display. So, change your code to do something instead:
maxTime = [[NSDate date] timeIntervalSince:startDate];
NSTimer is not guaranteed to be accurate, although in practice it usually is (if you're not doing anything else on your main thread...). However, it's perfectly reasonable for updating a display... just don't use the callback to calculate your timer. Save the current time when you start your timer, and get the difference between now and when you started every time the timer fires. Then it doesn't really matter how accurately NSTimer is firing, it only impacts how many times a second your on screen display updates.
I would like to know if there's a way to get the time elapsed when the battery increased of 5%. For example, how can I know how much time elapsed between 60% and 65% ? I think I could do this with NSTimer, but I'm not able to do this, can someone help me ?
Thanks a lot.
If you are doing this for a Mac, please check this question for how to get battery life in Mac;
If you are doing this for iOS, please check this question for how to get battery life in iOS.
Simply use your NSTimer to fire the function to get the battery life every x seconds and when it gets to 60%, capture a timestamp with NSDate, then when it gets to 65%, capture another timestamp and compare the two timestamps to get the time difference: SO question: how to get time between 2 NSDate objects.
Good luck.
EDIT:
All the methods to get the battery percentage are in either the first or second link based on your platform. If you want it to determine the time between now, and 5% up/down:
//both percent and date should be properties or instance variables (NSDate and float, respectively)
//You should probably also make the timer one as well, so you can stop it in any method with [tmr invalidate];
date = [NSDate date];
percent = [self getBatteryPercent];
NSTimer* tmr = [NSTimer scheduledTimerWithInterval:1 target:self selector:#selector(someMethod) userInfo:nil repeats:YES];
- (float)getBatteryPercent
{
//You'll have to get this code from one of those methods (first or second link)
}
- (void)someMethod
{
float newPercent = [self getBatteryPercent];
if(percent - newPercent == 5.0 || percent - newPercent == -5.0)
{
//Get the time between timestamps
NSDate* newDate = [NSDate date];
//See third link for how to get the time difference between date and newDate
}
}
The rest is up to you.
I'm trying to access the remaining time of an NSTimer X. I want to update the title of a button every second to reflect remaining mm:ss until zero. I couldn't find anything here.
For example: [btY setTitle:[What to insert here?] forState:UIControlStateSelected];
Or would you rather solve this in a different way?
You can use fireDate
NSTimer *timer = [NSTimer timerWithInterval:1.0 target:self selector:#selector(updateButton) userInfo:nil repeats:YES];
- (void)updateButton:(NSTimer*)timer
{
float timeRemaining = timer.fireDate.timeIntervalSinceNow;
// Format timeRemaining into your preferred string form and
// update the button text
}
This is generally not how you would solve this.
Create a repeating NSTimer set to the resolution at which you want to update the button instead.
So for instance, if you want your button to change every second until zero, create a NSTimer like so:
NSTimer *timer = [NSTimer timerWithInterval:1.0 target:self selector:#selector(updateButton) userInfo:nil repeats:YES];
Then implement updateButton; basically have a counter for remaining seconds, and every time updateButton gets called, decrease the counter by one, and update the title of the button.
You will not be able to get this kind of information, instead you will need to run the timer several times, for example, if you want to update the button with a text one time each 30 seconds, instead of starting a timer with 30 seconds start a timer with 1 sec and repeat it 30 times
I'm currently working on an app that will show a label that will start at zero, and count up to a number I specify. I wanted to do this using a simple loop like this one.
for (counterInt = 0; counterInt < 10; counterInt++)
{
NSLog(#"%i",counterInt);
}
The problem is, that this loop executes in less time than it takes for the view to appear on screen. My console logs 1-9 before the view finally loads with the label with showing 9. I've been researching for several hours trying to find a way to specify a duration for the loop and I can't seem to find any thing on this.
So my overall question is, is it possible to specify how long the loop should take to execute? If so, if anyone can point me in the right direction here it would be greatly appreciated!
Even if you slowed down the loop, it still wouldn't work. UI elements are only updated at the end of the run loop. You need to set up a timer and update the label in the method fired by the timer.
You're using the wrong approach. Try an NSTimer.
[NSTimer scheduledTimerWithTimeInterval:5.0
target:self
selector:#selector(incrementLabel:)
userInfo:nil
repeats:YES];
Then create a method called incrementLabel and have it increment an instance variable and update the label accordingly.
You can sleep a thread:
[NSThread sleepForTimeInterval:1];
However, jrturton and james supply the correct approach. I would place James' code in the viewDidAppear method so your label starts where you want it and the counter begins when the view appears.
In my iPhone app I want to have a UILabel which counts down to a certain date.
So far I have the user select a date from a UIDatePicker, but I can't figure out how to actually logically countdown each unit of the date. It needs to be live as well, so you can watch the date change rather than having to reload the view and see the difference from now until then.
I want to have a format like so (might change it up later, not sure):
dd / mm / yyyy
You will want an NSTimer to fire every time you wish to update the label and then you need to use NSDate's timeIntervalSinceNow method to get the time interval between your date and now. Then use that to update the label.
For instance:
- (void)startTimer {
...
// Set the date you want to count from
self.countdownDate = [NSDate date...]; ///< Get this however you need
// Create a timer that fires every second repeatedly and save it in an ivar
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(updateLabel) userInfo:nil repeats:YES];
...
}
- (void)updateLabel {
NSTimeInterval timeInterval = [self.countdownDate timeIntervalSinceNow]; ///< Assuming this is in the future for now.
/**
* Work out the number of days, months, years, hours, minutes, seconds from timeInterval.
*/
self.countdownLabel.text = [NSString stringWithFormat:#"%#/%#/%# %#:%#:%#", days, months, years, hours, minutes, seconds];
}
To get the actual number of days, months, years, hours, minutes & seconds you could also use NSCalendar and in particular the components:fromDate:toDate:options: method. Take a look at this question for some more discussion on that:
Number of days between two NSDates