（2）样例代码

import UIKit
import Charts
 
class ViewController: UIViewController, ChartViewDelegate {
     
    //折线图
    var chartView: LineChartView!
     
    override func viewDidLoad() {
        super.viewDidLoad()
         
        //创建折线图组件对象
        chartView = LineChartView()
        chartView.frame = CGRect(x: 20, y: 80, width: self.view.bounds.width - 40,
                                 height: 270)
        chartView.delegate = self //设置代理
        self.view.addSubview(chartView)
         
        //生成10条随机数据
        var dataEntries = [ChartDataEntry]()
        for i in 0..<10 {
            let y = arc4random()%100
            let entry = ChartDataEntry.init(x: Double(i), y: Double(y))
            dataEntries.append(entry)
        }
        //这10条数据作为1根折线里的所有数据
        let chartDataSet = LineChartDataSet(values: dataEntries, label: "图例1")
 
        //目前折线图只包括1根折线
        let chartData = LineChartData(dataSets: [chartDataSet])
         
        //设置折线图数据
        chartView.data = chartData
    }
     
    //折线上的点选中回调
    func chartValueSelected(_ chartView: ChartViewBase, entry: ChartDataEntry,
                            highlight: Highlight) {
        print("选中了一个数据")
        //显示该点的MarkerView标签
        self.showMarkerView(value: "\(entry.y)")
    }
     
    //显示MarkerView标签
    func showMarkerView(value:String){
        let marker = MarkerView(frame: CGRect(x: 20, y: 20, width: 80, height: 20))
        marker.chartView = self.chartView
        let label = UILabel(frame: CGRect(x: 0, y: 0, width: 80, height: 20))
        label.text = "数据：\(value)"
        label.textColor = UIColor.white
        label.font = UIFont.systemFont(ofSize: 12)
        label.backgroundColor = UIColor.gray
        label.textAlignment = .center
        marker.addSubview(label)
        self.chartView.marker = marker
    }
     
    //折线上的点取消选中回调
    func chartValueNothingSelected(_ chartView: ChartViewBase) {
        print("取消选中的数据")
    }
     
    //图表通过手势缩放后的回调
    func chartScaled(_ chartView: ChartViewBase, scaleX: CGFloat, scaleY: CGFloat) {
        print("图表缩放了")
    }
     
    //图表通过手势拖动后的回调
    func chartTranslated(_ chartView: ChartViewBase, dX: CGFloat, dY: CGFloat) {
       print("图表移动了")
    }
}

import Foundation
import Charts
 
open class BalloonMarker: MarkerImage
{
    open var color: UIColor
    open var arrowSize = CGSize(width: 15, height: 11)
    open var font: UIFont
    open var textColor: UIColor
    open var insets: UIEdgeInsets
    open var minimumSize = CGSize()
     
    fileprivate var label: String?
    fileprivate var _labelSize: CGSize = CGSize()
    fileprivate var _paragraphStyle: NSMutableParagraphStyle?
    fileprivate var _drawAttributes = [NSAttributedStringKey : AnyObject]()
     
    public init(color: UIColor, font: UIFont, textColor: UIColor, insets: UIEdgeInsets)
    {
        self.color = color
        self.font = font
        self.textColor = textColor
        self.insets = insets
         
        _paragraphStyle = NSParagraphStyle.default.mutableCopy()
            as? NSMutableParagraphStyle
        _paragraphStyle?.alignment = .center
        super.init()
    }
     
    open override func offsetForDrawing(atPoint point: CGPoint) -> CGPoint
    {
        var offset = self.offset
        var size = self.size
         
        if size.width == 0.0 && image != nil
        {
            size.width = image!.size.width
        }
        if size.height == 0.0 && image != nil
        {
            size.height = image!.size.height
        }
         
        let width = size.width
        let height = size.height
        let padding: CGFloat = 8.0
 
        var origin = point
        origin.x -= width / 2
        origin.y -= height
 
        if origin.x + offset.x < 0.0
        {
            offset.x = -origin.x + padding
        }
        else if let chart = chartView,
            origin.x + width + offset.x > chart.bounds.size.width
        {
            offset.x = chart.bounds.size.width - origin.x - width - padding
        }
         
        if origin.y + offset.y < 0
        {
            offset.y = height + padding;
        }
        else if let chart = chartView,
            origin.y + height + offset.y > chart.bounds.size.height
        {
            offset.y = chart.bounds.size.height - origin.y - height - padding
        }
         
        return offset
    }
     
    open override func draw(context: CGContext, point: CGPoint)
    {
        guard let label = label else { return }
         
        let offset = self.offsetForDrawing(atPoint: point)
        let size = self.size
         
        var rect = CGRect(
            origin: CGPoint(
                x: point.x + offset.x,
                y: point.y + offset.y),
            size: size)
        rect.origin.x -= size.width / 2.0
        rect.origin.y -= size.height
         
        context.saveGState()
         
        context.setFillColor(color.cgColor)
 
        if offset.y > 0
        {
            context.beginPath()
            context.move(to: CGPoint(
                x: rect.origin.x,
                y: rect.origin.y + arrowSize.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x + (rect.size.width - arrowSize.width) / 2.0,
                y: rect.origin.y + arrowSize.height))
            //arrow vertex
            context.addLine(to: CGPoint(
                x: point.x,
                y: point.y))
            context.addLine(to: CGPoint(
                x: rect.origin.x + (rect.size.width + arrowSize.width) / 2.0,
                y: rect.origin.y + arrowSize.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x + rect.size.width,
                y: rect.origin.y + arrowSize.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x + rect.size.width,
                y: rect.origin.y + rect.size.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x,
                y: rect.origin.y + rect.size.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x,
                y: rect.origin.y + arrowSize.height))
            context.fillPath()
        }
        else
        {
            context.beginPath()
            context.move(to: CGPoint(
                x: rect.origin.x,
                y: rect.origin.y))
            context.addLine(to: CGPoint(
                x: rect.origin.x + rect.size.width,
                y: rect.origin.y))
            context.addLine(to: CGPoint(
                x: rect.origin.x + rect.size.width,
                y: rect.origin.y + rect.size.height - arrowSize.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x + (rect.size.width + arrowSize.width) / 2.0,
                y: rect.origin.y + rect.size.height - arrowSize.height))
            //arrow vertex
            context.addLine(to: CGPoint(
                x: point.x,
                y: point.y))
            context.addLine(to: CGPoint(
                x: rect.origin.x + (rect.size.width - arrowSize.width) / 2.0,
                y: rect.origin.y + rect.size.height - arrowSize.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x,
                y: rect.origin.y + rect.size.height - arrowSize.height))
            context.addLine(to: CGPoint(
                x: rect.origin.x,
                y: rect.origin.y))
            context.fillPath()
        }
 
        if offset.y > 0 {
            rect.origin.y += self.insets.top + arrowSize.height
        } else {
            rect.origin.y += self.insets.top
        }
 
        rect.size.height -= self.insets.top + self.insets.bottom
         
        UIGraphicsPushContext(context)
         
        label.draw(in: rect, withAttributes: _drawAttributes)
         
        UIGraphicsPopContext()
         
        context.restoreGState()
    }
     
    /**
    open override func refreshContent(entry: ChartDataEntry, highlight: Highlight)
    {
        setLabel(String(entry.y))
    }
     **/
     
    open func setLabel(_ newLabel: String)
    {
        label = newLabel
         
        _drawAttributes.removeAll()
        _drawAttributes[.font] = self.font
        _drawAttributes[.paragraphStyle] = _paragraphStyle
        _drawAttributes[.foregroundColor] = self.textColor
         
        _labelSize = label?.size(withAttributes: _drawAttributes) ?? CGSize.zero
         
        var size = CGSize()
        size.width = _labelSize.width + self.insets.left + self.insets.right
        size.height = _labelSize.height + self.insets.top + self.insets.bottom
        size.width = max(minimumSize.width, size.width)
        size.height = max(minimumSize.height, size.height)
        self.size = size
    }
}

//显示MarkerView标签
func showMarkerView(value:String){
    //使用气泡状的标签
    let marker = BalloonMarker(color: UIColor(white: 180/255, alpha: 1),
                               font: .systemFont(ofSize: 12),
                               textColor: .white,
                               insets: UIEdgeInsets(top: 8, left: 8, bottom: 20, right: 8))
    marker.chartView = self.chartView
    marker.minimumSize = CGSize(width: 80, height: 40)
    marker.setLabel("数据：\(value)")
    self.chartView.marker = marker
}