公司项目 charts2.3 升到charts 3.0，marker标记报错， 然后找了很多方法， 后来用了官方看了官方的Demo终于知道该怎么做了

在charts2.3中， 用的是ChartMarker，但是在Charts3.0后就没有这个类， 替换成了MarkerView和MarkerImage， 实验了一下， 发现这两个都可以成功实现标记，而且区别不大！
上代码：MarkerView

import Foundation
import Charts

open class TBChartMarker: MarkerView
{
  open var color: UIColor?
  open var arrowSize = CGSize(width: 15, height: 11)
  open var font: UIFont?
  open var insets = UIEdgeInsets()
  open var minimumSize = CGSize()
  open var xAxisLabels: [String]!
  open var valuesCount: Int!
  
  fileprivate var labelns: NSString?
  fileprivate var _labelSize: CGSize = CGSize()
  fileprivate var _size: CGSize = CGSize()
  fileprivate var _paragraphStyle: NSMutableParagraphStyle?
  fileprivate var _drawAttributes = [String : AnyObject]()
 
  public init(color: UIColor, font: UIFont, insets: UIEdgeInsets)
  {
    super.init(frame: CGRect())   
    //super.init()   
    //使用MarkerView时， 没有关于MarkerView   init() 的方法， 这个时候会报错， 但是MarkerImage不会， 如果你可以麻烦给我说下你是怎么实现的！
    
    self.color = UIColor(red: 0.2, green: 0.2, blue: 0.2, alpha: 0.5)
    self.font = font
    self.insets = insets
    
    _paragraphStyle = NSParagraphStyle.default.mutableCopy() as? NSMutableParagraphStyle
    _paragraphStyle?.alignment = .center
  }
  
  required public init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  open override func draw(context: CGContext, point: CGPoint)
  {
    if (labelns == nil)
    {
      return
    }

    var rect = CGRect(
      origin: CGPoint(
        //        x: point.x + offset.x,
        //        y: point.y + offset.y),
        x: point.x,
        y: 40),
      size: _size)
    rect.origin.x -= _size.width / 2.0
    rect.origin.y -= _size.height
    
    context.saveGState()
    
    context.setFillColor((color?.cgColor)!)
    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))
    context.addLine(to: CGPoint(x: rect.origin.x + rect.size.width / 2.0, y: rect.origin.y + rect.size.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))
    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()
    
    rect.origin.y += self.insets.top
    rect.size.height -= self.insets.top + self.insets.bottom
    
    UIGraphicsPushContext(context)
    
    labelns?.draw(in: rect, withAttributes: _drawAttributes)
    
    UIGraphicsPopContext()
    
    context.restoreGState()
  }
  
  open override func refreshContent(entry: ChartDataEntry, highlight: Highlight)
  {
    let date = dateForDayOffset(valuesCount - Int(xAxisLabels[Int(entry.x)])! - 1)
    let formatter = DateFormatter()
    formatter.dateFormat = "MM月dd日"
    
    let dateString = formatter.string(from: date)

    let label = dateString.appending("\n\(Int(Double(entry.y.description)!))")
    print("description: \(entry.y.description)")
    labelns = label as NSString
    
    _drawAttributes.removeAll()
    _drawAttributes[NSFontAttributeName] = self.font
    _drawAttributes[NSParagraphStyleAttributeName] = _paragraphStyle
    _drawAttributes[NSForegroundColorAttributeName] = UIColor.white
    
    _labelSize = labelns?.size(attributes: _drawAttributes) ?? CGSize.zero
    _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)
  }
  
  fileprivate func dateForDayOffset(_ offset: Int) -> Date {
    let date = Date()
    let interval = -(offset * 60 * 60 * 24)
    let offsetDate = date.addingTimeInterval(TimeInterval(interval))
    return offsetDate
  }
}

MarkerImage：

import Foundation
import Charts

open class TBChartMarker: MarkerImage
{
  open var color: UIColor?
  open var arrowSize = CGSize(width: 15, height: 11)
  open var font: UIFont?
  open var insets = UIEdgeInsets()
  open var minimumSize = CGSize()
  open var xAxisLabels: [String]!
  open var valuesCount: Int!
  
  fileprivate var labelns: NSString?
  fileprivate var _labelSize: CGSize = CGSize()
  fileprivate var _size: CGSize = CGSize()
  fileprivate var _paragraphStyle: NSMutableParagraphStyle?
  fileprivate var _drawAttributes = [String : AnyObject]()
  
  
  
  
  public init(color: UIColor, font: UIFont, insets: UIEdgeInsets)
  {
   //super.init(frame: CGRect())
    super.init()
    
    self.color = UIColor(red: 0.2, green: 0.2, blue: 0.2, alpha: 0.5)
    self.font = font
    self.insets = insets
    
    _paragraphStyle = NSParagraphStyle.default.mutableCopy() as? NSMutableParagraphStyle
    _paragraphStyle?.alignment = .center
  }
  
  
  
  
  required public init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
 
 open override func offsetForDrawing(atPoint point: CGPoint) -> CGPoint {
   let size = self.size
   var points = point
   points.x -= size.width / 2.0
   points.y -= size.height
   return super.offsetForDrawing(atPoint: points)

}
  
  
  open override func draw(context: CGContext, point: CGPoint)
  {
    if (labelns == nil)
    {
      return
    }

    var rect = CGRect(
      origin: CGPoint(
        //        x: point.x + offset.x,
        //        y: point.y + offset.y),
        x: point.x,
        y: 40),
      size: _size)
    rect.origin.x -= _size.width / 2.0
    rect.origin.y -= _size.height
    
    context.saveGState()
    
    context.setFillColor((color?.cgColor)!)
    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))
    context.addLine(to: CGPoint(x: rect.origin.x + rect.size.width / 2.0, y: rect.origin.y + rect.size.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))
    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()
    
    rect.origin.y += self.insets.top
    rect.size.height -= self.insets.top + self.insets.bottom
    
    UIGraphicsPushContext(context)
    
    labelns?.draw(in: rect, withAttributes: _drawAttributes)
    
    UIGraphicsPopContext()
    
    context.restoreGState()
  }
  
  open override func refreshContent(entry: ChartDataEntry, highlight: Highlight)
  {
    let date = dateForDayOffset(valuesCount - Int(xAxisLabels[Int(entry.x)])! - 1)
    let formatter = DateFormatter()
    formatter.dateFormat = "MM月dd日"
    
    let dateString = formatter.string(from: date)

    let label = dateString.appending("\n\(Int(Double(entry.y.description)!))")
    print("description: \(entry.y.description)")
    labelns = label as NSString
    
    _drawAttributes.removeAll()
    _drawAttributes[NSFontAttributeName] = self.font
    _drawAttributes[NSParagraphStyleAttributeName] = _paragraphStyle
    _drawAttributes[NSForegroundColorAttributeName] = UIColor.white
    
    _labelSize = labelns?.size(attributes: _drawAttributes) ?? CGSize.zero
    _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)
  }
  
  fileprivate func dateForDayOffset(_ offset: Int) -> Date {
    let date = Date()
    let interval = -(offset * 60 * 60 * 24)
    let offsetDate = date.addingTimeInterval(TimeInterval(interval))
    return offsetDate
  }
}