如何等待两个独立的UIGraphicsImageRenderer任务完成

Question

我有两个带有不同呈现器的UIGraphicsImageRenderer任务，当我运行这个任务时，由于它是同步的，所以只返回一个任务，如何等待两个任务都创建了映像后才返回它们？

func createShareImage(callback: @escaping (_ image: UIImage, _ bgImage: UIImage) -> Void) {

    let canvas = UIView()
    ...

    let format = UIGraphicsImageRendererFormat()
    format.scale = UIScreen.main.scale

    let renderer = UIGraphicsImageRenderer(size: canvas.bounds.size, format: format)
    let stickerImage = renderer.image { _ in
        canvas.drawHierarchy(in: canvas.bounds, afterScreenUpdates: true)
    }

    let bgImageView = UIView()
    ...

    let bgRenderer = UIGraphicsImageRenderer(size: bgImageView.bounds.size, format: format)
    let bgImage = bgRenderer.image { _ in
        bgImageView.drawHierarchy(in: bgImageView.bounds, afterScreenUpdates: true)
    }

    callback(stickerImage, bgImage)
    
}

Answer 1

测试您的代码

func createShareImage(callback: @escaping (_ image: UIImage, _ bgImage: UIImage) -> Void) {

    let canvas = UIView(frame: CGRect.init(x: 0, y: 0, width: 200, height: 200))
    canvas.backgroundColor = .red
    let format = UIGraphicsImageRendererFormat()
    format.scale = UIScreen.main.scale
    print("1:",Thread.isMainThread)
    let renderer = UIGraphicsImageRenderer(size: canvas.bounds.size, format: format)
    let stickerImage = renderer.image { _ in
        canvas.drawHierarchy(in: canvas.bounds, afterScreenUpdates: true)
        print("2:",Thread.isMainThread)
    }

    let bgImageView = UIView(frame: CGRect.init(x: 0, y: 0, width: 2000, height: 2000))
    bgImageView.backgroundColor = .green
    let bgRenderer = UIGraphicsImageRenderer(size: bgImageView.bounds.size, format: format)
    let bgImage = bgRenderer.image { _ in
        bgImageView.drawHierarchy(in: bgImageView.bounds, afterScreenUpdates: true)
        print("3:",Thread.isMainThread)
    }

    print("4:",Thread.isMainThread)
    callback(stickerImage, bgImage)
}

获取

1: true
2: true
3: true
4: true

这意味着不存在异步部分，所有代码都是同步的和串行的，不需要等待。