Animating 5 views coordinated together

I'm trying to create my own loadbar; It consists of 5 bars, sliding in from the bottom from the left to the right, then sliding out to the top in the same order. There should be a fixed amount of time (say, 0.2 seconds) between all of them slid开发者_开发知识库ing in.

Currently, i'm using a timer to start them one by one, and then let themselves repeat. However, if there's some lag during start or something, they get messed up. The first two or sometimes 3 bars go almost simultaneously, the gap is bigger, just name it and it happened. I currently just set fixed times when each animation should start, but some lag makes them go bogus.

Any given bar moves up in about 0.3 seconds, waits there for 0.2 seconds, then moves further up in 0.3 seconds. They start 0.2 second after their left neighbour, from left to right. Once they started, they just repeat it.

So, what could i use to coordinate them in such a way, that there will always be the same amount of time between them?

Other things i have considered was just using a lot of images (but that will need lots of images i suppose), or using Key Value Observing (KVO) to see when the previous bar is at the desired height.

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According to the NSTimer documentation, NSTimer objects are not guaranteed to be realtime accurate on iOS.

A timer is not a real-time mechanism; it fires only when one of the run loop modes to which the timer has been added is running and able to check if the timer’s firing time has passed. 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.

It's an issue that effects NSTimer as well as OpenGL based games. Michael Daley mentions something similar in his book about how to set things up properly for an openGL based game. I suspect that this is suffering from the same similar situation.

That said, I would suggest preloading those images a adding them to the view just outside the bounds or frame of the visible view before you need then so that they are immediately available when you need them.

Addendum:

After thinking about this, I'm wondering if the C function wait() will help you here. It's a long shot, but perhaps it's worth a try. If not, then the answer may very well be that there is none.

Addendum 2:

I have no idea if this is going to help you either, but I found this page, which discusses pausing a program for less than a second.