斯威夫特 - 使用CGContext上用手指画出

Question

我试图做一个绘图应用程序。我有一个自定义的UIView：

class DrawView: UIView {

var touch : UITouch!
var lastPoint : CGPoint!
var currentPoint : CGPoint!

override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
    touch = touches.first as! UITouch
    lastPoint = touch.locationInView(self)
    println(lastPoint)
}

override func touchesMoved(touches: Set<NSObject>, withEvent event: UIEvent) {
    touch = touches.first as! UITouch
    currentPoint = touch.locationInView(self)

    self.setNeedsDisplay()

    lastPoint = currentPoint
}

override func drawRect(rect: CGRect) {
    var context = UIGraphicsGetCurrentContext()
    CGContextSetLineWidth(context, 5)
    CGContextSetStrokeColorWithColor(context, UIColor.blueColor().CGColor)
    CGContextSetLineCap(context, kCGLineCapRound)

    CGContextBeginPath(context)

    if lastPoint != nil {
        CGContextMoveToPoint(context, lastPoint.x, lastPoint.y)
        CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y)
    }

    CGContextStrokePath(context)
}

}

当我运行它，但是，我得到的是一个蓝点，随后我的手指，但没有台词？

我究竟做错了什么？

Answer 1

两件事情：

1. 调用self.setNeedsDisplay不会立即拨打drawRect。它只是设置一个标志，以便将drawRect在不久的将来被调用。既然你设置lastPoint从那之后，currentPoint权，当drawRect被称为lastPoint总是等于currentPoint。
2. drawRect重绘每次调用时整个视图，所以顶多你永远只能看到最近的线路。如果你固定的问题1，你必须按照你的手指，而不是一个点短线。如果你想看到整个线索，你需要点存储在一个数组，它是你的视图的属性，然后画线到所有的点连接在drawRect。

Answer 2

嗨，我做了一些简单的修改和固定代码，希望它可以帮助别人的未来（代码它的更新的斯威夫特3）：

class DrawView: UIView {

    var touch : UITouch!
    var lineArray : [[CGPoint]] = [[CGPoint]()]
    var index = -1

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        touch = touches.first! as UITouch
        let lastPoint = touch.location(in: self)

        index += 1
        lineArray.append([CGPoint]())
        lineArray[index].append(lastPoint)
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        touch = touches.first! as UITouch
        let currentPoint = touch.location(in: self)

        self.setNeedsDisplay()

        lineArray[index].append(currentPoint)
    }

    override func draw(_ rect: CGRect) {

        if(index >= 0){
            let context = UIGraphicsGetCurrentContext()
            context!.setLineWidth(5)
            context!.setStrokeColor((UIColor(red:0.00, green:0.38, blue:0.83, alpha:1.0)).cgColor)
            context!.setLineCap(.round)

            var j = 0
            while( j <= index ){
                context!.beginPath()
                var i = 0
                context?.move(to: lineArray[j][0])
                while(i < lineArray[j].count){
                    context?.addLine(to: lineArray[j][i])
                    i += 1
                }
                context!.strokePath()
                j += 1
            }
        }
    }
}