ios 使用简单的 CALayer 显示图像或 UIImage
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Display an image or UIImage with a plain CALayer
提问by Glenn Howes
I've often read that using a CALayerrather than a UIImageViewis an performance boost when it comes to heavy image usage. That makes sense, because UIImageViewcauses 3 copies of the image in memory, which is needed for Core Animation. But in my case I don't use Core Animation.
我经常读到，在大量使用图像时，使用 aCALayer而不是 aUIImageView可以提高性能。这是有道理的，因为UIImageView会在内存中生成 3 个图像副本，这是 Core Animation 所需要的。但就我而言，我不使用核心动画。
How can I assign a UIImage(or its image data) to a CALayerand then display it?
如何将 a UIImage（或其图像数据）分配给 aCALayer然后显示它？
回答by Glenn Howes
UIImage* backgroundImage = [UIImage imageNamed:kBackName];
CALayer* aLayer = [CALayer layer];
CGFloat nativeWidth = CGImageGetWidth(backgroundImage.CGImage);
CGFloat nativeHeight = CGImageGetHeight(backgroundImage.CGImage);
CGRect startFrame = CGRectMake(0.0, 0.0, nativeWidth, nativeHeight);
aLayer.contents = (id)backgroundImage.CGImage;
aLayer.frame = startFrame;
or in a Swift playground (you will have to provide your own PNG image in the Playground's resource file. I'm using the example of "FrogAvatar".)
或在 Swift 游乐场中（您必须在 Playground 的资源文件中提供您自己的 PNG 图像。我使用的是“FrogAvatar”示例。）
//: Playground - noun: a place where people can play
import UIKit
if let backgroundImage = UIImage(named: "FrogAvatar") // you will have to provide your own image in your playground's Resource file
{
let height = backgroundImage.size.height
let width = backgroundImage.size.width
let aLayer = CALayer()
let startFrame = CGRect(x: 0, y: 0, width: width, height: height)
let aView = UIView(frame: startFrame)
aLayer.frame = startFrame
aLayer.contentsScale = aView.contentScaleFactor
aLayer.contents = backgroundImage.cgImage
aView.layer.addSublayer(aLayer)
aView // look at this via the Playground's eye icon
}
回答by nevan king
ARC version requires a different cast:
ARC 版本需要不同的演员表：
self.myView.layer.contents = (__bridge id) self.myImage.CGImage;
回答by Denis Kutlubaev
CALayer *layer = [[CALayer alloc] init];
layer.contents = (__bridge id _Nullable)([UIImage imageNamed:@"REWIFISocketOff"].CGImage);
