如何在两点之间画一条线

Question

In my app I have an UIImageView where I can draw inside of that. How to draw a lines between two points in this way: The user press inside the UIImageView and when leave the press the code create the lines between the first CGPoint and the last CGPoint .

This is the code I've used to let drawing (Inside a touchesMoved delegate):

    let touch = touches.first

    let currentPoint = touch!.locationInView(imageView)

    let context = UIGraphicsGetCurrentContext()

    UIGraphicsBeginImageContext(self.imageView.frame.size)
    self.imageView.image?.drawInRect(CGRectMake(0, 0, self.imageView.frame.size.width,self.imageView.frame.size.height))
    CGContextMoveToPoint(context, lastPoint.x, lastPoint.y)
    CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y)
    CGContextSetLineCap(context,.Butt)
    CGContextSetLineWidth(context, 2.0)
    CGContextSetRGBStrokeColor(context,1.0, 1.0, 1.0, 1.0)
    CGContextStrokePath(context)
    self.imageView.image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    lastPoint = currentPoint

Answer 1

Try switching the order of these two lines:

let context = UIGraphicsGetCurrentContext()

UIGraphicsBeginImageContext(self.imageView.frame.size)

Since you're not in a drawRect method, it is very likely that UIGraphicsGetCurrentContext() will return nil initially, so you will be drawing to nothing. After you begin an image context, UIGraphicsGetCurrentContext() should return that context.