Xcode Objective-C | iOS: delay function / NSTimer

Question

So I'm developing my first iOS application and I need help..

Simple program for now, I have about 9 buttons and when I press the first button, or any button, I just want the first button to highlight for 60 milliseconds, unhighlight, second button highlights, wait 60 milliseconds, unhighlight and so on for the rest of the buttons so it looks like a moving LED.

I've looked tried sleep/usleep but once that sleep duration is done it seems like it skips the highlight/unhighlight all together.

For example:

- (void) button_circleBusy:(id)sender{
firstButton.enabled = NO;
sleep(1);
firstButton.enabled = YES;

and so on for the rest of the buttons. It DOES delay, but it doesn't delay the "firstButton.enabled = NO;". I have a picture for each button's "disabled state" and I never see it.

Any help's appreciated! I've looked into NSTimer but I was unsure on how to implement it.

Thanks.

-Paul

Answer 1

sleep doesn't work because the display can only be updated after your main thread returns to the system. NSTimer is the way to go. To do this, you need to implement methods which will be called by the timer to change the buttons. An example:

- (void)button_circleBusy:(id)sender {
    firstButton.enabled = NO;
    // 60 milliseconds is .06 seconds
    [NSTimer scheduledTimerWithTimeInterval:.06 target:self selector:@selector(goToSecondButton:) userInfo:nil repeats:NO];
}
- (void)goToSecondButton:(id)sender {
    firstButton.enabled = YES;
    secondButton.enabled = NO;
    [NSTimer scheduledTimerWithTimeInterval:.06 target:self selector:@selector(goToThirdButton:) userInfo:nil repeats:NO];
}
...

Answer 2

Try

NSDate *future = [NSDate dateWithTimeIntervalSinceNow: 0.06 ];
[NSThread sleepUntilDate:future];

Answer 3

Less code is better code.

[NSThread sleepForTimeInterval:0.06];

Swift:

Thread.sleep(forTimeInterval: 0.06)

Answer 4

A slightly less verbose way is to use the performSelector: withObject: afterDelay: which sets up the NSTimer object for you and can be easily cancelled

So continuing with the previous example this would be

[self performSelector:@selector(goToSecondButton) withObject:nil afterDelay:.06];

More info in the doc

Answer 5

I would like to add a bit the answer by Avner Barr. When using int64, it appears that when we surpass the 1.0 value, the function seems to delay differently. So I think at this point, we should use NSTimeInterval.

So, the final code is:

NSTimeInterval delayInSeconds = 0.05;

dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

//do your tasks here

});

Answer 6

int64_t delayInSeconds = 0.6;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
     do something to the button(s)
});