的UIImage不會在屏幕上顯示

Question

我有一個UIImage，我試圖在特定點進行顯示，但是當我打電話：

image.draw(at: CGPoint.zero) 

圖像從不顯露。但是，如果我創建的圖像UIImageView和ImageView的添加到我的視圖層次的UIStackViews之一，圖像清楚地顯示。我怎樣才能在窗口的原點畫出我的形象？

Answer 1

那些繪製方法不畫到UIWindow s/UIView s，它們畫到目前CGContext。

退房的文檔：https://developer.apple.com/reference/uikit/uiimage/1624132-draw「在目前情況下指定點繪製的圖像。」

例如：

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

如果你想有某種圖像視圖或任何以「漂浮在」您的應用程序，你可以做到這一點的容器視圖控制器。

以下示範操場一個簡單的例子，其中紅色廣場的形象圖「浮」在應用上面：

//: 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