尝试研究UIBezierPath，它将对您画线有很大帮助。这是文档。这是一个例子：

override func drawRect(rect: CGRect) {
    let aPath = UIBezierPath()

    aPath.move(to: CGPoint(x:<#start x#>, y:<#start y#>))
    aPath.addLine(to: CGPoint(x: <#end x#>, y: <#end y#>))

    // Keep using the method addLine until you get to the one where about to close the path
    aPath.close()

    // If you want to stroke it with a red color
    UIColor.red.set()
    aPath.lineWidth = <#line width#>
    aPath.stroke()
}

确保drawRect像上面的示例一样，将此代码放在中。

如果您需要更新工程图，只需致电setNeedsDisplay()进行更新。