为什么UIScrollView暂停我的CADisplayLink? [英] Why does UIScrollView pause my CADisplayLink?

问题描述

我有一个由CAEAGLLayer支持的视图，该视图位于UIScrollView内.当我开始滚动时，调用openGL视图的-draw方法的CADisplayLink停止调用.

I have a view backed by a CAEAGLLayer, which is inside a UIScrollView. When I begin scrolling, the CADisplayLink that calls the -draw method of openGL view stops getting called.

我验证了滚动时不会调用我的runloop start/stop方法. -draw方法根本不会在滚动开始后立即被调用，而是在滚动结束后立即被调用.

I verified that my runloop start / stop methods don't get called when scrolling. The -draw method simply doesn't get called as soon as scrolling begins, and resumes getting called as soon as scrolling ends.

UIKit是否会在滚动开始后立即停止CADisplayLink的触发?

Does UIKit stop a CADisplayLink from firing as soon as scrolling starts?

将显示链接添加到运行循环中，如下所示:

The display link is added to the run loop like this:

[dl addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

此运行循环模式和UIScrollView可能存在冲突吗?即使在UIScrollView滚动时，是否还有其他运行循环模式或替代解决方案可保持CADisplayLink触发?

Maybe there is a conflict with this run loop mode and UIScrollView? Are there other run loop modes or alternative solutions to keep a CADisplayLink firing even when a UIScrollView is scrolling?

我认为在任何应用程序中都可以有多个CADisplayLink.错了吗?

I thought there can be more than just one CADisplayLink in any application. Is that wrong?

推荐答案

滚动UIScrollView时您不在NSDefaultRunLoopMode中；您在UITrackingRunLoopMode中.因此，仅为前者安排的任何计时器都不会在后者中触发.您可以通过重复调用addToRunLoop:forMode:将CADisplayLink添加到多个运行循环模式，或使用NSRunLoopCommonModes对其进行一次调用，这涵盖了两种模式.

You're not in NSDefaultRunLoopMode while scrolling a UIScrollView; you're in UITrackingRunLoopMode. So any timer scheduled only for the former won't fire in the latter. You can add your CADisplayLink to multiple run loop modes by calling addToRunLoop:forMode: repeatedly, or call it once with NSRunLoopCommonModes, which covers both modes.

在WWDC 2012的会议223:使用滚动视图增强用户体验"中，他们详细讨论了此问题以及将滚动视图与GL集成的其他问题.我建议您观看视频，因为其中还有许多其他可能与您的情况.

They talked about this in detail, and other issues with integrating scroll views with GL, at WWDC 2012 in Session 223: "Enhancing User Experience with Scroll Views"; I recommend watching the video, as there's lots of other stuff in there that's likely relevant to your situation.

(2016)Swift3中的示例...

An example in (2016) Swift3...

let d = CADisplayLink(target: self, selector: #selector(ThisClassName.updateAlpha))
d.add(to: RunLoop.current, forMode: RunLoopMode.commonModes)


//and then, for example...
func updateAlpha() {
  let a = leader.layer.presentation()?.value(forKey: "opacity") as! CGFloat
  follower.alpha = a
  }

这篇关于为什么UIScrollView暂停我的CADisplayLink?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！