how to pass value between classes -

I have a the following code which is cocoa touch class, which draws a simple pie chart, and with the value CGFloat I can adjust the image to show the correct amount of Pie.

how can i pass a value for example from a slider in the main view controler.swift to it, instead of having it fixed?

    public class PieChart : NSObject {



    public class func drawCanvas1(ratio ratio: CGFloat = 0.75) {

        //// Variable Declarations
        let expression: CGFloat = 90 + ratio * 360


        let ovalPath = UIBezierPath(ovalInRect: CGRect(x: 0, y: -0, width: 112, height: 112))
        UIColor.blackColor().setFill()
        ovalPath.fill()



        let oval2Rect = CGRect(x: 4, y: 4, width: 104, height: 104)
        let oval2Path = UIBezierPath()
        oval2Path.addArcWithCenter(CGPoint(x: oval2Rect.midX, y: oval2Rect.midY), radius: oval2Rect.width / 2, startAngle: -expression * CGFloat(M_PI)/180, endAngle: -90 * CGFloat(M_PI)/180, clockwise: true)
        oval2Path.addLineToPoint(CGPoint(x: oval2Rect.midX, y: oval2Rect.midY))
        oval2Path.closePath()

        UIColor.redColor().setFill()
        oval2Path.fill()
    }
}

and this is my ViewController.swift

    import UIKit

class ViewController: UIViewController {


    @IBOutlet weak var sliderValue: UISlider!


    @IBAction func sliderMoved(sender: UISlider) {

        let mySliderValue = sliderValue.value

// this is where I'm stuck ->

        drawCanvas1 = Float(mySliderValue)


}

EDIT : Added code from where Piechart is Initialised

import UIKit


@IBDesignable


class PCView: UIView {

    /*
    // Only override drawRect: if you perform custom drawing.
    // An empty implementation adversely affects performance during animation.
    override func drawRect(rect: CGRect) {
        // Drawing code
    }
    */
    override func drawRect(rect: CGRect) {

        PieChart.drawCanvas1()

    }

}