I find dates very non-intuitive and confusing so here goes.
I have an array of events with dates and if the date of any single one is more than an hour in the past, I want to delete it.
Code I am using is:
NSDate *now = [NSDate date];
Events *event = mutableEventsArray[i];
if (event.date!=nil) {
NSTimeInterval sinceNow = [event.date timeIntervalSinceNow];
NSLog(#"sinceNow%#",sinceNow);
NSTimeInterval hourInterval = 3600;
if (sinceNow<hourInterval) {
[mutableEventsArray removeObjectAtIndex:i];
}
}
The problem is that it is removing events that are less than an hour in the past.
In one example I just ran, logging now to console shows:
Mon May 7 11:52:31 2018
Logging event.date shows: Mon May 7 11:35:42 2018
The difference is 17 minutes or about 1020 seconds, way less than an hour.
However, when I log the time interval sinceNow to console I am getting a negative number: sinceNow-97005.383634. This number is bigger than 3600 let alone 1020. So something seems wrong with the calculation NSTimeInterval sinceNow = [event.date timeIntervalSinceNow];
I have read that using NSTimeInterval does not take into account DaylightSavings Time and leap years, but don't see how that would be applicable here.
Would appreciate any suggestions on what issue might be.
You might be happier if you turn the calculation around:
NSTimeInterval ageOfEvent = [now timeIntervalSinceDate:event.date];
This gives ageOfEvent the meaning you expect: it is the elapsed time since the event, in seconds. So you can then say
if (ageOfEvent > 3600) {
[mutableEventsArray removeObjectAtIndex:i];
}
-[NSDate timeIntervalSinceNow] returns a negative value for a date in the past and a positive value for a date in the future.
To check if a date is more than an hour ago, you should check if timeIntervalSinceNow is < -3600
I'm developing a social media app and I need to implement a countdown timer that will keep running, even after the app is shutdown completely. Basically exactly how Snaps in Snapchat behave. Is there a way I can do this within the app, or does this need to be done from the database that will contain app records, users, friends, etc? I'm fairly new to Swift, and I'm using Swift 4, so please keep answers to Swift 3/4.
Thanks!
A good question to ask yourself is if a Timer is necessary or if you could simply just store a start Date and then calculate the current time compared to that stored start Date and check if it exceeds your countdown time. If you wanted to demonstrate a countdown timer in a UI similar to a snap in snapchat disappearing perhaps the following simple example would help:
let allowableViewTimeInterval = TimeInterval(10) // 10 Seconds
let refreshTimeInterval = TimeInterval(1) // 1 Second refresh time on the label
let snapOpenedDate = Date() // the date they opened the snap
let label = UILabel(frame: .zero) // a label to display the countdown
let timer = Timer.scheduledTimer(withTimeInterval: refreshTimeInterval, repeats: true) {
let currentDate = Date()
let calendar = Calendar.current
let dateComponents = calendar.components(CalendarUnit.CalendarUnitSecond, fromDate: snapOpenedDate, toDate: currentDate, options: nil)
let seconds = dateComponents.second
label.text = "\(seconds)"
}
// If the countdown finishes or a user leaves the snap we need to make sure we invalidate the timer.
timer.invalidate()
You can then adapt this to your solution by storing the snapOpenedDate and looking it up again when an app resumes from background.
This question already has answers here:
How can I make a countdown timer like in a music player?
(2 answers)
Closed 7 years ago.
I'm trying to make an app that tell us the rest of time from the present time till one hour later.
This is the code but now it only has a function that tell us the countdown time by decreasing one second from the present time.
I'm thinking that I haven't definite the definition of the "cnt"
so that's why I'm thinking it doesn't work.
Can somebody tell me the reason and a solution?
import UIKit
class ViewController: UIViewController {
var cnt : Int = 0
var timer : NSTimer!//NSTimerというデフォルト機能から引っ張る
var myInt:Int = 0
override func viewDidLoad() {
let myDate: NSDate = NSDate()
let myCalendar: NSCalendar = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian)!
let myComponents = myCalendar.components([.Year, .Hour, .Minute, .Second],
fromDate: myDate) // myDate、すなわちNSDateから要素として引っ張り出してる
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "onUpdate:", userInfo: nil, repeats: true)//カウントダウンのインターバル
timer.fire()
var myStr: String = "\(myComponents.hour)"
myStr += "\(myComponents.minute)"
myStr += "\(myComponents.second)"
myInt = Int(myStr)! // toInt()がSwift2より無効になったようです。myInt=Str(my components,hour,minute,second)=現時刻
}
func onUpdate(timer : NSTimer){
cnt += 1//cnt+1=cnt,
let count = myInt - cnt //残り時間＝現在時刻ー現在時刻に１時間足した時刻
print(count) // println()は、Swift2よりDeprecatedになりました。
}
}
It is difficult to understand what you're asking, but I will do my best.
In your viewDidLoad method, you're setting myInt to the integer representation of myStr. If the time is 18:30:50, myInt will be equal to 183050. That is not an appropriate representation of the time. Time is base 60, integers are base 10, for one thing. If you want to represent time as a single number, you can use timeIntervalSinceDate, or timeIntervalSinceReferenceDate or timeIntervalSince1970 to get the NSTimeInterval (ie. fractional seconds) representation of the date relative to a certain epoch either of your choosing or one built into Foundation.
Subtracting 1 from myInt each time the timer fires isn't going to give you an indication of the time remaining.
Also, NSTimer is not an accurate way to keep time. You should instead save the start date as a property and determine the time remaining based on timeIntervalSinceDate
e.g.
func onUpdate(timer : NSTimer){
let currentTime = NSDate()
let timeElapsed = currentTime.timeIntervalSinceDate(myDate)
println(timeElapsed)
}
If you want to show time elapsed in minutes, you can divide it by 60. You can look into NSDateComponentsFormatter to easily get a string representation of time intervals.
If you want the countdown to stop after an hour, then check for when timeElapsed is over 3600.
If you want it to show a countdown from 1 hour, then subtract the timeElapsed from 3600.
trying to figure out how to get the time passed since timer started.
this is what i did :
Feel free to suggest other ways to get the time passed since the page loaded
Declared timer :
var runner = NSTimer()
runner = NSTimer.scheduledTimerWithTimeInterval(0.6, target: self, selector: Selector("time"), userInfo: nil, repeats: true)
Than tried this in the function,returns the interval i set(obviously)
func time() {
println(self.runner.timeInterval)
}
anyway if getting how much time passes since it started? (it's in the didload section so it like saying how much time passes since the page loaded). thanks ! :D
Put this in a playground. I added the loop just to create a time lag. Time in seconds down to fractions of a second.
var startTime = NSDate.timeIntervalSinceReferenceDate()
var currentTime: NSTimeInterval = 0
for var i = 0; i < 10000; i++ {
if i == 99 {
currentTime = NSDate.timeIntervalSinceReferenceDate()
println(i)
}
}
var elapsedTime = currentTime - startTime
println(Double(elapsedTime))
From:
https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSDate_Class/#//apple_ref/occ/instp/NSDate/timeIntervalSinceReferenceDate
timeIntervalSinceReferenceDate
Returns the interval between the date object and January 1, 2001, at 12:00 a.m. GMT. (in seconds)
The method is establishing a startTime whenever you want to start. It is a time in seconds since the reference. Later we set the currentTime to be equal to the new time since the reference time. Subtracting one from the other gives elapsed time. There is several decimal place precision.
What is the best way to get the current system time milliseconds?
If you're looking at using this for relative timing (for example for games or animation) I'd rather use CACurrentMediaTime()
double CurrentTime = CACurrentMediaTime();
Which is the recommended way; NSDate draws from the networked synch-clock and will occasionally hiccup when re-synching it against the network.
It returns the current absolute time, in seconds.
If you want only the decimal part (often used when syncing animations),
let ct = CACurrentMediaTime().truncatingRemainder(dividingBy: 1)
[[NSDate date] timeIntervalSince1970];
It returns the number of seconds since epoch as a double. I'm almost sure you can access the milliseconds from the fractional part.
I benchmarked all the other answers on an iPhone 4S and iPad 3 (release builds). CACurrentMediaTime has the least overhead by a small margin. timeIntervalSince1970 is far slower than the others, probably due to NSDate instantiation overhead, though it may not matter for many use cases.
I'd recommend CACurrentMediaTime if you want the least overhead and don't mind adding the Quartz Framework dependency. Or gettimeofday if portability is a priority for you.
iPhone 4S
CACurrentMediaTime: 1.33 µs/call
gettimeofday: 1.38 µs/call
[NSDate timeIntervalSinceReferenceDate]: 1.45 µs/call
CFAbsoluteTimeGetCurrent: 1.48 µs/call
[[NSDate date] timeIntervalSince1970]: 4.93 µs/call
iPad 3
CACurrentMediaTime: 1.25 µs/call
gettimeofday: 1.33 µs/call
CFAbsoluteTimeGetCurrent: 1.34 µs/call
[NSDate timeIntervalSinceReferenceDate]: 1.37 µs/call
[[NSDate date] timeIntervalSince1970]: 3.47 µs/call
In Swift we can make a function and do as follows
func getCurrentMillis()->Int64{
return Int64(NSDate().timeIntervalSince1970 * 1000)
}
var currentTime = getCurrentMillis()
Though its working fine in Swift 3.0 but we can modify and use the Date class instead of NSDate in 3.0
Swift 3.0
func getCurrentMillis()->Int64 {
return Int64(Date().timeIntervalSince1970 * 1000)
}
var currentTime = getCurrentMillis()
To get milliseconds for current date.
Swift 4+:
func currentTimeInMilliSeconds()-> Int
{
let currentDate = Date()
let since1970 = currentDate.timeIntervalSince1970
return Int(since1970 * 1000)
}
So far I found gettimeofday a good solution on iOS (iPad), when you want to perform some interval evaluation (say, framerate, timing of a rendering frame...) :
#include <sys/time.h>
struct timeval time;
gettimeofday(&time, NULL);
long millis = (time.tv_sec * 1000) + (time.tv_usec / 1000);
Swift 2
let seconds = NSDate().timeIntervalSince1970
let milliseconds = seconds * 1000.0
Swift 3
let currentTimeInMiliseconds = Date().timeIntervalSince1970.milliseconds
It may be useful to know about CodeTimestamps, which provide a wrapper around mach-based timing functions. This gives you nanosecond-resolution timing data - 1000000x more precise than milliseconds. Yes, a million times more precise. (The prefixes are milli, micro, nano, each 1000x more precise than the last.) Even if you don't need CodeTimestamps, check out the code (it's open source) to see how they use mach to get the timing data. This would be useful when you need more precision and want a faster method call than the NSDate approach.
http://eng.pulse.me/line-by-line-speed-analysis-for-ios-apps/
// Timestamp after converting to milliseconds.
NSString * timeInMS = [NSString stringWithFormat:#"%lld", [#(floor([date timeIntervalSince1970] * 1000)) longLongValue]];
I needed a NSNumber object containing the exact result of [[NSDate date] timeIntervalSince1970]. Since this function was called many times and I didn't really need to create an NSDate object, performance was not great.
So to get the format that the original function was giving me, try this:
#include <sys/time.h>
struct timeval tv;
gettimeofday(&tv,NULL);
double perciseTimeStamp = tv.tv_sec + tv.tv_usec * 0.000001;
Which should give you the exact same result as [[NSDate date] timeIntervalSince1970]
CFAbsoluteTimeGetCurrent()
Absolute time is measured in seconds relative to the absolute reference date of Jan 1 2001 00:00:00 GMT. A positive value represents a date after the reference date, a negative value represents a date before it. For example, the absolute time -32940326 is equivalent to December 16th, 1999 at 17:54:34. Repeated calls to this function do not guarantee monotonically increasing results. The system time may decrease due to synchronization with external time references or due to an explicit user change of the clock.
This is basically the same answer as posted by #TristanLorach, just recoded for Swift 3:
/// Method to get Unix-style time (Java variant), i.e., time since 1970 in milliseconds. This
/// copied from here: http://stackoverflow.com/a/24655601/253938 and here:
/// http://stackoverflow.com/a/7885923/253938
/// (This should give good performance according to this:
/// http://stackoverflow.com/a/12020300/253938 )
///
/// Note that it is possible that multiple calls to this method and computing the difference may
/// occasionally give problematic results, like an apparently negative interval or a major jump
/// forward in time. This is because system time occasionally gets updated due to synchronization
/// with a time source on the network (maybe "leap second"), or user setting the clock.
public static func currentTimeMillis() -> Int64 {
var darwinTime : timeval = timeval(tv_sec: 0, tv_usec: 0)
gettimeofday(&darwinTime, nil)
return (Int64(darwinTime.tv_sec) * 1000) + Int64(darwinTime.tv_usec / 1000)
}
Try this :
NSDate * timestamp = [NSDate dateWithTimeIntervalSince1970:[[NSDate date] timeIntervalSince1970]];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"YYYY-MM-dd HH:mm:ss.SSS"];
NSString *newDateString = [dateFormatter stringFromDate:timestamp];
timestamp = (NSDate*)newDateString;
In this example, dateWithTimeIntervalSince1970 is used in combination of the formatter #"YYYY-MM-dd HH:mm:ss.SSS" that will return the date with year, month, day and the time with hours, minutes, seconds, and milliseconds. See the example : "2015-12-02 04:43:15.008". I used the NSString to be sure that the format will be has written before.
func currentmicrotimeTimeMillis() -> Int64{
let nowDoublevaluseis = NSDate().timeIntervalSince1970
return Int64(nowDoublevaluseis*1000)
}
let timeInMiliSecDate = Date()
let timeInMiliSec = Int (timeInMiliSecDate.timeIntervalSince1970 * 1000)
print(timeInMiliSec)
This is what I used for Swift
var date = NSDate()
let currentTime = Int64(date.timeIntervalSince1970 * 1000)
print("Time in milliseconds is \(currentTime)")
used this site to verify accuracy http://currentmillis.com/
NSTimeInterval time = ([[NSDate date] timeIntervalSince1970]); //double
long digits = (long)time; //first 10 digits
int decimalDigits = (int)(fmod(time, 1) * 1000); //3 missing digits
/*** long ***/
long timestamp = (digits * 1000) + decimalDigits;
/*** string ***/
NSString *timestampString = [NSString stringWithFormat:#"%ld%03d",digits ,decimalDigits];
[NSDate timeIntervalSinceReferenceDate] is another option, if you don't want to include the Quartz framework. It returns a double, representing seconds.