ios Swift图表问题

我使用Charts iOS库（https://github.com/danielgindi/Charts），我有以下代码：

import UIKit
import Charts


    class ChartsViewController: UIViewController , ChartViewDelegate{

        var lineChartView: LineChartView?
        let months = ["Jan" , "Feb", "Mar", "Apr", "May", "June", "July", "August", "Sept", "Oct", "Nov", "Dec"]
        let dollars1 = [1453.0,2352,5431,1442,5451,6486,1173,5678,9234,1345,9411,2212]

        override func viewDidLoad() {
            super.viewDidLoad()

            self.lineChartView = LineChartView(frame: CGRectMake(50, 70, 300, 300))
            self.lineChartView!.delegate = self
            self.lineChartView!.descriptionText = "Tap node for details"
            self.lineChartView!.drawGridBackgroundEnabled = false
            self.lineChartView!.descriptionTextColor = UIColor.whiteColor()
            self.lineChartView!.noDataText = "No data provided"
            setChartData(months)
            self.view.addSubview(self.lineChartView!)



        }
        func setChartData(months : [String]) {

            var yVals1 : [ChartDataEntry] = [ChartDataEntry]()
            for var i = 0; i < months.count; i++ {
                yVals1.append(ChartDataEntry(value: dollars1[i], xIndex: i))
            }

            let set1: LineChartDataSet = LineChartDataSet(yVals: yVals1, label: "First Set")
            set1.lineWidth = 10.0
            set1.circleRadius = 0.0 // the radius of the node circle
            set1.fillColor = UIColor.redColor()
            set1.highlightColor = UIColor.yellowColor()
            set1.drawCircleHoleEnabled = false
            set1.drawVerticalHighlightIndicatorEnabled = false
            var dataSets : [LineChartDataSet] = [LineChartDataSet]()
            dataSets.append(set1)
            let data: LineChartData = LineChartData(xVals: months, dataSets: dataSets)
            data.setValueTextColor(UIColor.whiteColor())
            self.lineChartView!.data = data            
        }

我得到这个：

https://postimg.org/image/6z6nk5nkn/

我的问题是这样的：

我想删除背景上的网格（垂直和水平线），但是我无法删除网格，因为在官方库文档中找不到任何内容。

你能帮助我吗？