iPhone: How to get current milliseconds?

问题:

What is the best way to get the current system time milliseconds?

回答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.

回答2:

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)

回答3:

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

iPad 3

回答4:

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()

回答5:

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  struct timeval time; gettimeofday(&time, NULL); long millis = (time.tv_sec * 1000) + (time.tv_usec / 1000);

回答6:

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/

回答7:

Swift 2

let seconds = NSDate().timeIntervalSince1970 let milliseconds = seconds * 1000.0

Swift 3

let currentTimeInMiliseconds = Date().timeIntervalSince1970.milliseconds

回答8:

// Timestamp after converting to milliseconds.  NSString * timeInMS = [NSString stringWithFormat:@"%lld", [@(floor([date timeIntervalSince1970] * 1000)) longLongValue]];

回答9:

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  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]

回答10: