D28 - 用 Swift 和公开资讯，打造投资理财的 Apps { 三大法人成交比重实作.3 }

金额计算的部分，在前一篇就完成了，这一篇开始讲 pie chart 的实作。

分析我们要做的事情

设置 PieChartView
依最新的三大法人资讯日期为 key，找出对应 key 的当日台股成交量
依照台股成交量计算三大法人成交比重
将成交比重的值转成 PieChartData
将 PieChartView.data 的值设定好并渲染

1 - 设置 Pie Chart View 的基本 UI

// MARK: ui methods
    private func setup(chartView: PieChartView) {
        
        chartView.usePercentValuesEnabled = true
        chartView.drawSlicesUnderHoleEnabled = false
        chartView.holeRadiusPercent = 0.58
        chartView.transparentCircleRadiusPercent = 0.61
        chartView.chartDescription?.enabled = false
        chartView.setExtraOffsets(left: 5, top: 10, right: 5, bottom: 5)
        
        chartView.drawCenterTextEnabled = true
        
        chartView.drawHoleEnabled = false
        chartView.rotationEnabled = true
        chartView.highlightPerTapEnabled = true
        
        chartView.entryLabelColor = .darkText
        
        let l = chartView.legend
        l.horizontalAlignment = .right
        l.verticalAlignment = .top
        l.orientation = .vertical
        l.drawInside = false
        l.xEntrySpace = 7
        l.yEntrySpace = 0
        l.yOffset = 0
        l.textColor = .black
        //        chartView.legend = l
    }

2 - 依最新的三大法人资讯日期为 key，找出对应 key 的当日台股成交量

/// 获得当下三大法人日期的大盘资讯
    private func getMarketTradingInfo() -> TwMarketTradingInfo? {
        
        let timeInterval = date.timeIntervalSince1970
        
        for info in dailyTradingInfo {
            
            if info.date.timeIntervalSince1970 == timeInterval {
                return info
            }
        }
        return nil
    }

3 - 依照台股成交量计算三大法人成交比重

4 - 将成交比重的值转成 PieChartData

在第 3 步要注意的是，getPieChartData 传进来的值是 [买进 + 卖出] 的值，但比重的计算上，应该是 [买进 + 卖出] / 2 才是合理的。因为台股总成交金额 == 总买进金额 == 总卖出金额，所以要相加除以2。

private func getPieChartData(threeMajorTrading: Double, twMarketTrading: Double) -> PieChartData {
        
				// 三大法人传入值是加总，所以要除以台股总成交後，再除以 2 
        let threeMajorPercentage = (threeMajorTrading / twMarketTrading) / 2

        let nonThreeMajorPercentage = 1 - threeMajorPercentage
        
        let threeMajorTradingData = PieChartDataEntry(value: threeMajorPercentage, label: "三大法人交易额")
        let nonThreeMajorTradingData = PieChartDataEntry(value: nonThreeMajorPercentage, label: "非三大法人交易额")
        
        let dataSet = PieChartDataSet(entries: [threeMajorTradingData, nonThreeMajorTradingData])
        dataSet.colors = [.systemGreen, .systemBlue]
        let data = PieChartData(dataSet: dataSet)
        data.setValueTextColor(.darkText)
        return data
    }

5 - 呼叫上列所有 func 并渲染 pie chart view

/// 计算三大法人占股市交易的额度
    private func updatePieChartThreeMajorPercentage() {
        
        guard let twMarketTradingInfo = getMarketTradingInfo(),
              let threeMajor = totalMajorInvestorInfo?.total else {
            print("找不到和三大法人同日的大盘成交资讯，请检查资料来源")
            return
        }
        
        let threeMajorTrading = threeMajor.totalBuy + threeMajor.totalSell
        let twMarketTrading = twMarketTradingInfo.value ?? 0

        let data = getPieChartData(threeMajorTrading: threeMajorTrading, twMarketTrading: twMarketTrading)
        
        pieChartView.data = data
    }

最後，让这些 func 在 button 中发动

@IBAction func drawPieChartButtonDidTap(_ sender: Any) {
        setup(chartView: self.pieChartView)
        updatePieChartThreeMajorPercentage()
    }

完成这一步的 UI 如下