Question

我有UIImage我试图在特定点展示，但是当我打电话时：

image.draw(at: CGPoint.zero)

图片永远不会显示。但是，如果我使用图片创建UIImageView并将该图像视图添加到视图层次结构中的UIStackViews之一，则图像会清晰显示。如何在窗口的原点绘制图像？

Answer 1

这些绘制方法不会绘制到UIWindow s / UIView，它们会绘制到当前CGContext。

查看文档：{{3}}“在当前上下文中的指定点绘制图像。”

例如：

UIGraphicsBeginImageContext(image.size)
image.draw(at: CGPoint.zero)
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

如果你想要某种图像视图或任何“漂浮在你的应用程序之上”，你可以使用容器视图控制器。

这是一个操场，显示了一个快速示例，其中红色正方形是一个“浮动”在应用程序上方的图像视图：

https://developer.apple.com/reference/uikit/uiimage/1624132-draw

//: Playground - noun: a place where people can play

import UIKit
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

class ContainerViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor.white
        addImageViewOverlay()
    }

    func addImageViewOverlay() {
        let overlayImageView = UIImageView()
        overlayImageView.backgroundColor = UIColor.red
        overlayImageView.translatesAutoresizingMaskIntoConstraints = false

        view.addSubview(overlayImageView)
        overlayImageView.widthAnchor.constraint(equalToConstant: 50.0).isActive = true
        overlayImageView.heightAnchor.constraint(equalToConstant: 50.0).isActive = true
        overlayImageView.topAnchor.constraint(equalTo: view.topAnchor, constant: 10.0).isActive = true
        overlayImageView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 10.0).isActive = true
    }

    func embed(childController: UIViewController) {
        // In a real application you'd remove the existing child controller first
        addChildViewController(childController)

        childController.view.translatesAutoresizingMaskIntoConstraints = false

        view.insertSubview(childController.view, at: 0)
        childController.didMove(toParentViewController: self)

        childController.view.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        childController.view.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        childController.view.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
        childController.view.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
    }

}

let containerController = ContainerViewController(nibName: nil, bundle: nil)
containerController.view.frame = CGRect(x: 0.0, y: 0.0, width: 320.0, height: 480.0)

let applicationController = UITabBarController(nibName: nil, bundle: nil)

let tabOneController = UIViewController(nibName: nil, bundle: nil)
tabOneController.title = "One"

let tabTwoController = UIViewController(nibName: nil, bundle: nil)
tabTwoController.title = "Two"

applicationController.viewControllers = [tabOneController, tabTwoController]

containerController.embed(childController: applicationController)

PlaygroundPage.current.liveView = containerController.view

UIImage不会在屏幕上显示

1 个答案: