使用普通的 CALayer 显示图像或 UIImage

Question

我经常读到，在大量使用图像时，使用 CALayer 而不是 UIImageView 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，这是核心动画所需的。但就我而言，我不使用核心动画。

如何将 UIImage （或其图像数据）分配给 CALayer 然后显示它？

Answer 1

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;

或者在 Swift Playground 中（您必须在 Playground 的资源文件中提供自己的 PNG 图像。我使用的是“FrogAvatar”的示例。）

  //: 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 

Answer 2

ARC 版本需要不同的演员表：

self.myView.layer.contents = (__bridge id) self.myImage.CGImage;

Answer 3

CALayer *layer = [[CALayer alloc] init];
layer.contents = (__bridge id _Nullable)([UIImage imageNamed:@"REWIFISocketOff"].CGImage);