Change LineColor Stroke when graph already displayed

[inkrementz]

I have my Graph already displayed. If I tap on a button, i'd like to change the strokecolor of the lineLayer. So I added this in the class:

public func changeLineColor(color : UIColor) {    
  lineLayer?.strokeColor = color.CGColor
}

But if I call it from my view like: myGraph.changeLineColor(myColor) , it will return the error:

fatal error: use of unimplemented initializer 'init(layer:)' for class 'TestGraph.ScrollableGraphViewDrawingLayer'

I can still change the background color by adding this function and it works:

public func changeBackgroundColor(color : UIColor) {
drawingView.backgroundColor = color
}

BUT do you have any idea why I can't change the linecolor ? :/ thanks !!