定时器常用来做一些定时任务,iOS定时 实现有如下
NSTimer,0.1s 误差 50-100 milliseconds.
dispatch_source_set_timer,
CADisplayLink 每秒 60 帧,间隔 16.67 ms
dispatch_after
performSelector() after
mach_timebase_info_data_t 最高精度,可以达到 nano妙
/// RepeatingTimer mimics the API of DispatchSourceTimer but in a way that prevents
/// crashes that occur from calling resume multiple times on a timer that is
/// already resumed (noted by https://github.com/SiftScience/sift-ios/issues/52
class RepeatingTimer {
let timeInterval: TimeInterval
init(timeInterval: TimeInterval) {
self.timeInterval = timeInterval
}
private lazy var timer: DispatchSourceTimer = {
let t = DispatchSource.makeTimerSource()
t.schedule(deadline: .now() + self.timeInterval, repeating: self.timeInterval)
t.setEventHandler(handler: { [weak self] in
self?.eventHandler?()
})
return t
}()
var eventHandler: (() -> Void)?
private enum State {
case suspended
case resumed
}
private var state: State = .suspended
deinit {
timer.setEventHandler {}
timer.cancel()
/*
If the timer is suspended, calling cancel without resuming
triggers a crash. This is documented here https://forums.developer.apple.com/thread/15902
*/
resume()
eventHandler = nil
}
func resume() {
if state == .resumed {
return
}
state = .resumed
timer.resume()
}
func suspend() {
if state == .suspended {
return
}
state = .suspended
timer.suspend()
}
}
网友评论