我有一个自定义的 UIView
类,它使用 UIGraphicsImageRenderer
绘制一些线条,我有一些 slider 来更改用于绘制线条的点,但这样做并没有不要删除旧线,它只是在它们上面绘制新线。我试过在方法的顶部和底部附近添加 self.setNeedsDisplay()
,两者都没有任何区别。
我从 hackingwithswift project 27 中了解了如何使用 UIGraphicsImageRenderer
的基本概念- 在那个项目中,他使用 switch 语句调用不同的函数来绘制不同的东西,这似乎可以很好地清除和重绘东西。
我也尝试过 var clearsContextBeforeDrawing: Bool = true
,但我认为我没有正确使用它,我在文档中找到了它。
我还在 setNeedsDisplay
文档中看到它说“您应该使用此方法请求仅当 View 的内容或外观发生变化时才重绘 View 。如果您只是更改 View , View 通常不会重绘”—我猜测“ View 的几何形状”是指转换(缩放/平移/旋转)之类的东西?
func drawLines(pointList: [CGPoint],
cycle: Bool = false,
lineColor: CGColor = UIColor.blue.cgColor,
fillColor: CGColor = UIColor.clear.cgColor) {
// self.setNeedsDisplay()
let renderer = UIGraphicsImageRenderer(size: CGSize(width: 728, height: 984))
// var clearsContextBeforeDrawing: Bool = true
let img = renderer.image { ctx in
ctx.cgContext.move(to: pointList[0])
for v in pointList.dropFirst() {
ctx.cgContext.addLine(to: v)
}
ctx.cgContext.setStrokeColor(lineColor)
ctx.cgContext.strokePath()
}
let iv = UIImageView(image:img)
iv.frame.origin = CGPoint(x: 0, y: 0)
self.addSubview(iv)
// self.setNeedsDisplay()
}
最佳答案
每次调用 drawLines()
时,您都会添加一个新的 UIImageView
。您的代码编写方式,每个 ImageView 都有清晰的背景...因此您会看到“线条”彼此叠加。
您应该已经将一个 UIImageView
添加到self
(我们称它为theDrawingImageView
),并且然后更改您的函数以结束:
//let iv = UIImageView(image:img)
//iv.frame.origin = CGPoint(x: 0, y: 0)
//self.addSubview(iv)
theDrawingImageView.image = img
}
编辑:这是一个完整的演示。您可以直接在 playground 页面中运行它。
它创建一个 View Controller 并添加一个 UIButton
和一个 UIImageView
。每次点击按钮时,将生成一组 12 个随机点并用于在新的 UIImage
上绘制线条,然后用于设置 .image
属性 ImageView 。
import UIKit
import PlaygroundSupport
class TestViewController : UIViewController {
let theDrawingImageView: UIImageView = {
let v = UIImageView()
v.backgroundColor = UIColor.lightGray
v.translatesAutoresizingMaskIntoConstraints = false
return v
}()
let btn: UIButton = {
let b = UIButton()
b.setTitle("Tap to Draw Lines", for: .normal)
b.backgroundColor = .red
b.translatesAutoresizingMaskIntoConstraints = false
return b
}()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor(red: 0.25, green: 0.5, blue: 1.0, alpha: 1.0)
// add button and image view to self.view
self.view.addSubview(btn)
self.view.addSubview(theDrawingImageView)
// button position
btn.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
btn.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 20.0).isActive = true
// image view position
theDrawingImageView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
theDrawingImageView.topAnchor.constraint(equalTo: btn.bottomAnchor, constant: 20.0).isActive = true
// image view width and height
theDrawingImageView.widthAnchor.constraint(equalToConstant: 300.0).isActive = true
theDrawingImageView.heightAnchor.constraint(equalToConstant: 300.0).isActive = true
// add a target for the button tap
btn.addTarget(self, action: #selector(btnTapped(_:)), for: .touchUpInside)
}
// simple random number function
func random(_ range:Range<Int>) -> Int {
return range.lowerBound + Int(arc4random_uniform(UInt32(range.upperBound - range.lowerBound)))
}
func btnTapped(_ sender: Any) {
var pts = [CGPoint]()
let maxX = Int(theDrawingImageView.bounds.size.width)
let maxY = Int(theDrawingImageView.bounds.size.height)
// generate a set of 12 random points
for _ in 1...12 {
let x = random(0..<maxX)
let y = random(0..<maxY)
let pt = CGPoint(x: x, y: y)
pts.append(pt)
}
drawLines(imageView: theDrawingImageView, pointList: pts)
}
func drawLines(imageView: UIImageView,
pointList: [CGPoint],
cycle: Bool = false,
lineColor: CGColor = UIColor.blue.cgColor,
fillColor: CGColor = UIColor.clear.cgColor) {
let renderer = UIGraphicsImageRenderer(size: imageView.bounds.size)
// this creates a new UIImage and draws lines on it
let img = renderer.image { ctx in
ctx.cgContext.move(to: pointList[0])
for v in pointList.dropFirst() {
ctx.cgContext.addLine(to: v)
}
ctx.cgContext.setStrokeColor(lineColor)
ctx.cgContext.strokePath()
}
// set the image view's .image to the new image with the lines drawn on it
imageView.image = img
}
}
let vc = TestViewController()
PlaygroundPage.current.liveView = vc
关于ios - 如何使用 Swift 在 iOS 中刷新/重绘/重新加载 UIGraphicsImageRenderer,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46078906/