ios - 带计时器的绘图应用程序。绘图时间少于 20 秒后计时器开始滞后
问题描述
我在一些朋友的帮助下构建了这个应用程序。我真的不知道代码是如何工作的。
基本上使用苹果铅笔记录数据(平板电脑上的时间,苹果铅笔的速度,笔画计数等)。然而,随着时间的流逝和更多的绘图发生,计时器与实时不同步。
这个应用程序的目的是用于痴呆症研究,我让患者在平板电脑上画画,然后收集相关信息。如果计时器发臭,我无法进行研究。
我尝试禁用所有计时器,但延迟保持不变。我有一种感觉,这与笔画的采样方式有关。我只需要一个笔画数,我不需要它来显示每分钟的笔画数(这是它目前正在做的事情)。我认为中风计数器可能是原因???
这是程序: https ://drive.google.com/open?id=1lwzKwG7NLcX1qmE5yoxsdq5HICV2TNHm
class StrokeSegment {
var sampleBefore: StrokeSample?
var fromSample: StrokeSample!
var toSample: StrokeSample!
var sampleAfter: StrokeSample?
var fromSampleIndex: Int
var segmentUnitNormal: CGVector {
return segmentStrokeVector.normal!.normalized!
}
var fromSampleUnitNormal: CGVector {
return interpolatedNormalUnitVector(between: previousSegmentStrokeVector, and: segmentStrokeVector)
}
var toSampleUnitNormal: CGVector {
return interpolatedNormalUnitVector(between: segmentStrokeVector, and: nextSegmentStrokeVector)
}
var previousSegmentStrokeVector: CGVector {
if let sampleBefore = self.sampleBefore {
return fromSample.location - sampleBefore.location
} else {
return segmentStrokeVector
}
}
var segmentStrokeVector: CGVector {
return toSample.location - fromSample.location
}
var nextSegmentStrokeVector: CGVector {
if let sampleAfter = self.sampleAfter {
return sampleAfter.location - toSample.location
} else {
return segmentStrokeVector
}
}
init(sample: StrokeSample) {
self.sampleAfter = sample
self.fromSampleIndex = -2
}
@discardableResult
func advanceWithSample(incomingSample: StrokeSample?) -> Bool {
if let sampleAfter = self.sampleAfter {
self.sampleBefore = fromSample
self.fromSample = toSample
self.toSample = sampleAfter
self.sampleAfter = incomingSample
self.fromSampleIndex += 1
return true
}
return false
}
}
class StrokeSegmentIterator: IteratorProtocol {
private let stroke: Stroke
private var nextIndex: Int
private let sampleCount: Int
private let predictedSampleCount: Int
private var segment: StrokeSegment!
init(stroke: Stroke) {
self.stroke = stroke
nextIndex = 1
sampleCount = stroke.samples.count
predictedSampleCount = stroke.predictedSamples.count
if (predictedSampleCount + sampleCount) > 1 {
segment = StrokeSegment(sample: sampleAt(0)!)
segment.advanceWithSample(incomingSample: sampleAt(1))
}
}
func sampleAt(_ index: Int) -> StrokeSample? {
if index < sampleCount {
return stroke.samples[index]
}
let predictedIndex = index - sampleCount
if predictedIndex < predictedSampleCount {
return stroke.predictedSamples[predictedIndex]
} else {
return nil
}
}
func next() -> StrokeSegment? {
nextIndex += 1
if let segment = self.segment {
if segment.advanceWithSample(incomingSample: sampleAt(nextIndex)) {
return segment
}
}
return nil
}
}
例如,在真正的 25 秒时,应用程序会在 20 秒时显示总时间。
解决方案
ATimer
不是计算经过时间的东西。它是一种用于在经过一段时间后触发执行的工具。但是只是“在”一段时间过去之后,而不是“恰好在”一段时间过去之后。因此,例如执行以下操作:
var secondsElapsed: TimeInterval = 0.0
let timeInitiated = Date()
Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in
secondsElapsed += 1
print("\(secondsElapsed) seconds should have passed but in reality \(Date().timeIntervalSince(timeInitiated)) second have passed")
}
您会看到两者并不相同,但非常接近。但是一旦我添加了一些额外的工作,如下所示:
var secondsElapsed: TimeInterval = 0.0 让 timeInitiated = Date()
func countTo(_ end: Int) {
var string = ""
for i in 1...end {
string += String(i)
}
print("Just counted to string of lenght \(string.count)")
}
Timer.scheduledTimer(withTimeInterval: 1.0/60.0, repeats: true) { _ in
countTo(100000)
}
Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in
secondsElapsed += 1
print("\(secondsElapsed) seconds should have passed but in reality \(Date().timeIntervalSince(timeInitiated)) second have passed")
}
我们会遇到像“应该已经过了 14.0 秒,但实际上已经过了 19.17617702484131 秒”这样的情况。
我们让应用程序繁忙,所以它没有时间正确计数。
在您的情况下,您将需要使用以下两种解决方案之一:
- 如果您对经过的时间感兴趣,只需
timeIntervalSince
按照第一个代码片段中的说明使用。 - 如果您需要确保每秒钟触发一次
N
,您应该优化您的代码,考虑多线程......但主要记住,您只能接近“N
每秒钟”,不可能保证每秒钟执行一次N
。