提高自定义 UIView 的绘图性能
我有一个自定义的 UIView，它由许多图像组成，它们的位置随着用户触摸而变化。 该视图必须跟踪用户触摸，而我在绘制此类视图时遇到性能瓶颈，导致我无法实时跟踪输入。
一开始，我在 [UIView drawRect:] 方法中绘制所有内容，当然它太慢了，因为即使没有必要，所有内容都会重新绘制。 然后，我使用更多的 CALayers 来仅更新正在更改的层，这给了我更好的响应能力。 但是，当我必须在一个图层上多次绘制相同的图像时，最多需要 500 毫秒。
由于图像放置在固定位置，是否有办法预先绘制它们？我是否应该考虑将它们放入多个 CALayers 中并隐藏/显示它们？ 另外，我不明白为什么存在 [CALayer setNeedsDisplayInRect:] 但委托（显然）无法知道无效的矩形是什么来优化绘图。
解决方案
按照答案中的建议，我最终为图像创建了许多 CALayers，并在第一次显示图层时设置了 contents 属性。这是一种延迟加载的妥协：在第一次尝试中，我在创建时设置了每个图层的内容，但这导致在程序启动时预先绘制任何可能的图像，从而将应用程序冻结几秒钟。
I have a custom UIView which is composed of many images, their positions are changing in response to the user touch.
The view must track the user touch and i'm experiencing a performance bottleneck in the drawing of such view, preventing me to follow the input in realtime.
At the beginning i was drawing everything in the [UIView drawRect:] method and of course it was way too slow because everything was redrawn even if not necessary.
Then, i used more CALayers to update only the layer that was changing and this gave me much better responsiveness.
But still, when i have to draw the same image many times on a layer it takes up to 500ms.
Since the images are placed at fixed positions it there a way to pre-draw them? Should i consider putting them in many CALayers and just hide/show them?
Also, i don't understand why a [CALayer setNeedsDisplayInRect:] exists but the delegate has (apparently) no way to know what the invalid rect is to optimize the drawing.
Solution
Following the advice in the answer I finally created many CALayers for the images and set the contents property the first time the layer was being shown. This is a lazy-loading compromise: in a first attempt i set the contents of every layer at the creation time but this caused to pre-draw any possible image on the program launch, freezing the application for seconds.
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（1）
来自 -[CALayer drawInContext:] 的文档：
显示的默认实现在自动创建的上下文上调用drawInContext：；大概也设置了边界框（大概被传递给drawRect:）。
如果您要绘制多张静态图像，我只需将每张图像粘贴到其自己的 UIView 中即可；我不认为开销有那么大（如果是的话，CALayer 开销应该更小）。如果它们都有动画，我肯定会使用 UIView/CALayer。如果其中一些动画没有（太多）并且您发现速度明显缓慢，则可以预渲染它们。这是在drawRect:（或类似的）中渲染和GPU上的图层合成之间的权衡，但总的来说，我认为后者要快得多。
From the documentation for -[CALayer drawInContext:]:
The default implementation of display calls drawInContext: on an automatically-created context; presumably setting the bounding box as well (which is presumably passed to drawRect:).
If you're drawing several static images, I'd just stick each one in its own UIView; I don't think the overhead is that big (if it is, the CALayer overhead should be smaller). If they all animate, I'd definitely use UIView/CALayer. If some of them don't animate (much) and you notice significant slowness, you can pre-render those. It's a trade-off between rendering in drawRect: (or similar) and layer compositing on the GPU, but in general I'd assume that the latter is much faster.