CODEWITHSUNDEEP
iosswiftswift3uiimagecore-graphics
shoe
shoe

Reputation: 1070

UIImage won't show on screen

I have a UIImage that I'm trying to display at a particular point, but when I call:

image.draw(at: CGPoint.zero)

the image never shows. However, if I create a UIImageView with the image and add that imageview to one of the UIStackViews in my view hierarchy, the image is clearly shown. How can I draw my image at the window's origin?

Upvotes: 0

Views: 59

Answers (1)

user498982
user498982

Reputation:

Those draw methods don't draw to UIWindows / UIViews, they draw to the current CGContext.

Check out the documentation: https://developer.apple.com/reference/uikit/uiimage/1624132-draw "Draws the image at the specified point in the current context."

For example:

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

If you want to have some sort of image view or whatever to "float above" your application, you can do that with a container view controller.

Here's a playground that shows a quick example where the red square is an image view "floating" above the application:

Playground Example

//: 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

Upvotes: 4

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