Swift 3.0 - 用手指在 imageView 上绘图

我一直致力于使用 swift 3.0 在图像视图上绘制红线，并遇到了一些问题。正如您可能猜到的那样，我正在使用堆栈溢出中的一些代码来帮助我进行第一次初步尝试，但遇到了一个奇怪的错误。

当我在图像视图上拖动手指时，它确实绘制了一条红线，但对于每个“帧”，它都会丢弃我在屏幕上进一步绘制的所有内容。因此，当我绘制时，看起来我正在绘制的线条正在下降，然后完全消失在屏幕之外。

我正在寻找的是能够简单地在图像视图上绘图，而不是每帧都向下移动，我希望它保持在相同的位置，类似于它在所有绘图应用程序等上的工作方式。

下面是全部代码：

@IBOutlet weak var mainImageView: UIImageView!
var lastPoint = CGPoint.zero
var fromPoint = CGPoint();
var toPoint = CGPoint.zero
var red: CGFloat = 255.0
var green: CGFloat = 0.0
var blue: CGFloat = 0.0
var brushWidth: CGFloat = 10.0
var opacity: CGFloat = 1.0
var swiped = false

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint)
{
    UIGraphicsBeginImageContextWithOptions(self.mainImageView.bounds.size, false, 0);
    mainImageView.image?.draw(in: CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height))
    let context = UIGraphicsGetCurrentContext()

    context?.move(to: fromPoint)
    context?.addLine(to: toPoint)
    context?.setLineCap(CGLineCap.round)
    context?.setLineWidth(brushWidth)
    context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0)
    context?.setBlendMode(CGBlendMode.normal)
    context?.strokePath()

    mainImageView.image = UIGraphicsGetImageFromCurrentImageContext()
    mainImageView.alpha = opacity
    UIGraphicsEndImageContext()

}
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = false;
    if let touch = touches.first {
        lastPoint = touch.location(in: self.mainImageView)
    }
}
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = true;
    if let touch = touches.first {
        let currentPoint = touch.location(in: mainImageView)
        drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)
        lastPoint = currentPoint
    }
}
override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    if(!swiped){
        self.drawLineFrom(fromPoint: lastPoint, toPoint: lastPoint)
    }
}

感谢各位的帮助！

通过以下代码，您可以使用触摸绘制图像（Swift 3.0）

func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
swiped = false
if let touch = touches.first as? UITouch {
    lastPoint = touch.location(in: self.view)
}
 }
 func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) {

UIGraphicsBeginImageContext(view.frame.size)
let context = UIGraphicsGetCurrentContext()
tempImageView.image?.draw(in: CGRect(x: 0, y: 0, width:     view.frame.size.width, height: view.frame.size.height))


context?.move(to: fromPoint)
context?.addLine(to: toPoint)

context?.setLineCap(CGLineCap.round)
context?.setLineWidth(brushWidth)
context?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0)
context?.setBlendMode(CGBlendMode.normal)
context?.strokePath()


tempImageView.image = UIGraphicsGetImageFromCurrentImageContext()
tempImageView.alpha = opacity
UIGraphicsEndImageContext()

}

 func touchesMoved(touches: Set<NSObject>, withEvent event: UIEvent) {
swiped = true
if let touch = touches.first as? UITouch {
    let currentPoint = touch.location(in: view)
    drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)

    lastPoint = currentPoint
}
}