I want some operation executed every second. I do not want ticks to be accurate between every two seconds. But for a long term, I want them exact for average.
For example, the ticks may happen in time sequence like this:
0.999, 2.005, 2.995, 3.950, 5.012, ... 999.01, 1000.011, ...
Functions may not executed exactly per second, but in a long term, there would be no (or little enough) error in average.
A simple way is using NSTimer. But there is a problem: If CPU ratio is high, the NSTimer fires with a tinny delay. For example, it may fires as a sequence like this:
1.001, 2.002, 3.004, 4.005, 5.006, ... 999.999, 1001.001, ...
As time elapses, the time error may go more and more greater.
Therefore, is there any way to capture any time elapse event in Xcode? Something like "NSTimeNotificationSecondPassed" or ...?
I have develop a method to achieve my goal:
Create an thread Like This:
- (void)_threadHandleTick:(id)arg
{
while(...)
{
#autoreleasepool
{
[self sleepToNextSecond];
... /* Do what ever you like or raise a noification */
}
}
}
Then the - sleepToNextSecond method:
- (void)sleepToNextSecond
{
NSDateFormatter *microSecondFormat = [[NSDateFormatter alloc] init];
[microSecondFormat setDateFormat:#"SSSSSS"];
NSString *microSecondString = [microSecondFormat stringFromDate:[NSDate date]];
useconds_t microSeconds = 1000000 - ((useconds_t)[microSecondString integerValue]);
usleep(microSeconds);
}
Done.
Related
I created a simple maths based app. The app asks a user 6 multiplication table questions. e.g. Q1 10 x 10
The user enters an answer
The app displays whether the user's answer was correct or incorrect and displays this using the following
IBOutlet NSTextField *CorrectIncorrect;
In a cycle of the app (1 question of 6) CorrectIncorrect is used to display the strings 'correct' or 'incorrect' using this line of code
[CorrectIncorrect setStringValue:receivedAnswer];
[[CorrectIncorrect window] display];
Then as the next question is posed to the user, the either string is cleared using the following code.
[CorrectIncorrect setStringValue:#""];
[[CorrectIncorrect window] display];
Initially, each CorrectIncorrect string was being cleared to quickly, so the user never saw if their answer was 'correct' or 'incorrect'. I therefore used a time delay method to slow the process in order to allow the user to see the display before it was cleared.see below
- (void)TimeDelay
{
startInterval = [NSDate timeIntervalSinceReferenceDate];
stopInterval = [NSDate timeIntervalSinceReferenceDate];
while ((stopInterval - startInterval) <= 1)
{
stopInterval = [NSDate timeIntervalSinceReferenceDate];
}
}
This worked fine in Xcode 5. Does not work in Xcode 7.3.1. Any advice appreciated.
Few things:
1) Time interval is in seconds, so <= 1 really isn't much time, have you tried increasing that time and seeing what it looks like?
2) You should also consider adding a button like "Go to next question". That way you won't need to have a timer
3) If you want to have a timer to reset the string, you should just use Grand Central Dispatch
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 10 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
[CorrectIncorrect setStringValue:#""];
});
one-ish line, and is more intuitive
I've made a game in Xcode 6, using several NSTimers for different things, like a scorer timer, countdown timer, and to move my objects around. The problem is that sometimes (it seems like) the NSTimers stop for like half a second which makes it look like it lags. Example: When the character is moving, it stops for a tiny second and then continues to move. It happens so fast, but it is noticable, and it annoys me so much. I want it to be completely smooth. Any help would be appreciated!
A couple of thoughts:
If you're having a small delay in the timer processing, the most likely issue is that you have something blocking the main queue. Take a careful look at your code and see if you can find anything that could block the main queue.
You can actually use Instruments to find places in your app where the thread might be blocked. If I recall correctly, WWDC 2112 video Building Concurrent User Interfaces on iOS shows the trick with Instruments to find where your app is blocked. It's a bit dated, but the techniques for finding where the main thread blocks still apply.
It's unlikely, but you might want to consider checking the run loop modes that your timer is running on. For example, the default:
[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(tick:) userInfo:nil repeats:YES];
This can pause during certain animations. You might consider using a broader array of run loop modes, e.g.:
NSTimer *timer = [NSTimer timerWithTimeInterval:1.0 target:self selector:#selector(tick:) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
This results in a timer that is less susceptible to certain delays during particular types of animations. It just depends upon what else your app is doing when you see the delay in the user interface.
When using a timer to update animations, better than a NSTimer is a CADisplayLink. For example, define a few properties:
#property (nonatomic, strong) CADisplayLink *displayLink;
#property (nonatomic) CFTimeInterval startTime;
Then you can write code to start and stop the display link:
- (void)startDisplayLink
{
self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:#selector(handleDisplayLink:)];
self.startTime = CACurrentMediaTime();
[self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}
- (void)stopDisplayLink
{
[self.displayLink invalidate];
self.displayLink = nil;
}
- (void)handleDisplayLink:(CADisplayLink *)displayLink
{
CFTimeInterval elapsed = CACurrentMediaTime() - self.startTime;
// update your UI, not on the basis of "this is called x times per second",
// but rather, on the basis that `elapsed` seconds have passed
}
The key in good animation code is that you don't just assume that your routine will be called at a specified frequency, but rather that you update the UI based upon the number of elapsed seconds. This way, a slow device that drops a few frames and a fast device will yield the same animation, the latter would just be a little smoother than the former.
The merits of display links, though, are discussed briefly in WWDC 2014 video - Building Interruptible and Responsive Interactions. There are other longer discussions of the topic that are eluding me at this point, but this might be a good place to get introduced to the topic (even though the vast majority of that video is on other topics).
You may want to try a high resolution timer, like Timer dispatch sources. It looks a bit scary at first, but actually quite easy to use. Sample code (with comments)
dispatch_source_t CreateDispatchTimer(uint64_t interval, uint64_t leeway, dispatch_queue_t queue , dispatch_block_t block) {
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
if (timer) {
// Use dispatch_time instead of dispatch_walltime if the interval is small
dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), interval, leeway);
dispatch_source_set_event_handler(timer, block);
dispatch_resume(timer);
}
return timer;
}
void MyCreateTimer()
{
dispatch_source_t aTimer = CreateDispatchTimer(30 * NSEC_PER_SEC, 1 * NSEC_PER_SEC, dispatch_get_main_queue(), ^{
NSLog(#"Timer fired!");
});
// Keep a reference if you want to, say, stop it somewhere in the future
}
EDIT:
In XCode, if you type dispatch in the editor, it will suggest a snippet called dispatch_source timer - GCD: Dispatch Source (Timer), which will generate the template code for the timer.
I ran the following code expecting to schedule three subsequent calls, at different time intervals (e.g. after 1 sec, after 2.6sec etc..) on the method "displayWarningMessage" but didn't work (it displayed the massage only the first time).
I don't find a method signature in the scheduler that would do the job of displaying it multiple times and with a specific delay. Anyone has some suggestion?
[self scheduleOnce:#selector(displayWarningMessage) delay:0.7f];
[self scheduleOnce:#selector(displayWarningMessage) delay:1.7f];
[self scheduleOnce:#selector(displayWarningMessage) delay:3.7f];
Problem here is, when you call first schedule it is scheduled successfully. But the next immediate call is throwing warning something
CCScheduler#scheduleSelector. Selector already scheduled. Updating interval from: X.2 to X.2
you can see this in the log.
What you can do is when the selector is called, at the end of the method you can schedule it again for the next time, until you are done. You may take a counter to keep track of how many times it has been called, put all of your intervals in an array and then schedule next selector for the interval at the specific index identified by counter. like this:
NSArray *intervals = [NSArray arrayWithObjects:[NSNumber numberWithFloat:0.7],[NSNumber numberWithFloat:1.7],[NSNumber numberWithFloat:3.7], nil];
int counter = 0;
//schedule it for the first time with object at index counter/index 0
[self scheduleOnce:#selector(displayWarningMessage) delay:[(NSNumber *)[intervals objectAtIndex:counter]] floatValue];
now in your selector, do something like this:
-(void)displayWarningMessage
{
//do all your stuff here
//increment counter
counter ++;
if(counter < [intervals count])
{
//schedule it for the next time with object at index counter/index
[self scheduleOnce:#selector(displayWarningMessage) delay:[(NSNumber *)[intervals objectAtIndex:counter]] floatValue];
}
}
intervals and counter should be class ivars of-course.
Try this:
- (void)displayWarningMessage {
//Stuff
}
- (void)callStuff {
CCCallFunc *call = [CCCallFunc actionWithTarget:self selector:#selector(displayWarningMessage)];
CCDelayTime *delay1 = [CCDelayTime actionWithDuration:0.7f];
CCDelayTime *delay2 = [CCDelayTime actionWithDuration:1.7f];
CCDelayTime *delay3 = [CCDelayTime actionWithDuration:3.7f];
CCSequence *actionToRun = [CCSequence actions:delay1, call, delay2, call, delay3, call, nil];
[self runAction:actionToRun];
}
That should work for what you're trying to do, at least that's how I'd imagine doing it. I'm fairly sure you can call that CCCallFunc multiple times in one CCSequence without having to create it three individual times. You could also make those delays variable based if need be, of course. Let me know how it goes.
Method is created.
[self schedule: #selector(displayWarningMessage:) interval:3.2f];
-(void) displayWarningMessage:(ccTime) delta
{
CCLOG(#"alert........!!!!!!");
}
Use the Calling method in not warning message detected.
I am wondering if there is some way that I can create a timer that countdown from a given time. For example, say I want this timer to last an hour. There will be a NSTextField that will show the time remaining (ex. 25 minutes), and will auto update every minute to the new value. And then, when an hour is finally passed, it will run some function. I have seen people suggesting NSTimer and NSDate for this, but am wondering what you all could suggest.
Thanks!
EDIT: My current code (timeInstance is an instance variable):
- (void)awakeFromNib:
{
timeInstance = [[NSDate date] addTimeInterval:(10 * 60)];
[timeInstance retain];
[timer invalidate];
timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:#selector(timer:) userInfo:NULL repeats:YES];
}
- (void)timer:(NSTimer *)myTimer
{
NSDate *now = [NSDate date];
// Compare
}
NSTimer and NSDate sounds perfectly reasonable.
EDIT: As a side note, it might be a good idea to increase the frequency as the target time approaches; allowing you to change from hour display to minute display to second display.
I have got two timevalues in the format: %H%M%S (E.G.161500)
These values are text-based integers.
Is there a simple function in Cocoa that calculates the difference between these two integers using a 60 seconds and minutes scale?
So if
time 1 = 161500
time 2 = 171500
timedifference = 003000
NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateFormat:#"HHmmss"];
NSDate *date1 = [dateFormatter dateFromString:#"161500"];
NSDate *date2 = [dateFormatter dateFromString:#"171500"];
NSTimeInterval diff = [date2 timeIntervalSinceDate:date1]; // diff = 3600.0
The class for manipulating dates is NSDate. The method for getting time intervals is -timeIntervalSinceDate:. The result is a NSTimeInterval value, which is a double representing the interval in seconds.
You can create a NSDate object from a NSString with +dateWithString:, provided that your date is formatted as 2001-03-24 10:45:32 +0600.
try this code.
- (NSTimeInterval)intervalBetweenDate:(NSDate *)dt1 andDate:(NSDate *)dt2 {
NSTimeInterval interval = [dt2 timeIntervalSinceDate:dt1];
NSLog(#"%f",interval);
return interval;
}
I would create an NSFormatter subclass to parse time values in that format from input data (you can put one on a text field to automatically convert user input, or use it to parse from a data source in code). Have it return the combined number of seconds as an NSTimeInterval (double representing seconds) wrapped in an NSNumber. From there it's easy to subtract the difference, and display it using the same NSFormatter class you created. In both parsing and displaying values, you're the one responsible to write code converting from seconds to hours:minutes:seconds or whatever format you like. You could also convert these values to an NSDate like mouviciel mentioned, if it makes sense for your application. Just keep in mind you're always going to be storing the time difference from a reference date, usually Jan 1st 1970 (NSDate has methods to do this for you).