Swift不会绘制图表（XYPieChart）

我正在使用该XYPieChart库来在我的项目中绘制饼图，但是当我在模拟器中运行该饼图时，它不会绘制该饼图。我在一UITableViewController堂课上尝试过，但结果没有切换到UIViewController相同的结果。我在这里做错了什么？

import Foundation
import XYPieChart

class MainVC:UIViewController,XYPieChartDelegate,XYPieChartDataSource{

    let z = Share.sharedInstance
    let dbm = DatabaseManager()
    var chart_dNameArr = [""]
    var chart_dAmountArr = [0.0]

    override func viewDidLoad() {
        self.view.addGestureRecognizer(self.revealViewController().panGestureRecognizer())
        makeChart()
    }

    func makeChart(){
        let pieChart = XYPieChart()
        let viewWidth: Float = Float(pieChart.bounds.size.width / 2)
        let viewHeight: Float = Float(pieChart.bounds.size.height / 2)
        pieChart.delegate = self
        pieChart.dataSource = self
        pieChart.startPieAngle = CGFloat(M_PI_2)
        pieChart.animationSpeed = 1.5
        pieChart.labelColor = UIColor.whiteColor()
        pieChart.labelShadowColor = UIColor.blackColor()
        pieChart.showPercentage = true
        pieChart.backgroundColor = UIColor.whiteColor()
        //To make the chart at the center of view
        pieChart.pieCenter = CGPointMake(pieChart.bounds.origin.x + CGFloat(viewWidth), pieChart.bounds.origin.y + CGFloat(viewHeight))
        //Method to display the pie chart with values.
        pieChart.reloadData()

        print("made a chart")
    }

    func numberOfSlicesInPieChart(pieChart: XYPieChart!) -> UInt {
      return 2
    }

    func pieChart(pieChart: XYPieChart!, valueForSliceAtIndex index: UInt) -> CGFloat {
        var value: CGFloat = 0.0
        if index % 2 == 0 {
            value = 25
        }
        else {
            value = 75
        }
        return value
    }

    func pieChart(pieChart: XYPieChart!, colorForSliceAtIndex index: UInt) -> UIColor! {
        var color: UIColor
        if index % 2 == 0 {
            color = UIColor.redColor()
        }
        else {
            color = UIColor.greenColor()
        }
        return color
    }     
}