我做了一个小应用程序测量心率从iWatch。图表按预期显示当前心率，但我对设计有几个问题。下面你可以找到我的图表的图像和它在swift中的设置。

// chart set up
self.chtChart.delegate = self as? ChartViewDelegate
self.chtChart.noDataTextColor = UIColor.white
self.chtChart.noDataText = "Press Start button to display the chart"

let set_a: LineChartDataSet = .init(entries: [ChartDataEntry(x: Double(Int(0)), y: self.valueHR)], label: "BPM")
set_a.drawCirclesEnabled = false
set_a.setColor(UIColor.systemPink)
set_a.drawValuesEnabled = false
set_a.lineWidth = 5.0

// remove vertical grid and labels
self.chtChart.xAxis.drawGridLinesEnabled = false
self.chtChart.rightAxis.drawLabelsEnabled = false
self.chtChart.xAxis.drawLabelsEnabled = false

// change label 'BPM' color
self.chtChart.legend.textColor = UIColor.white
// change left numbers (bpm values)
self.chtChart.leftAxis.labelTextColor = UIColor.white
// change right border line color
self.chtChart.rightAxis.axisLineColor = UIColor.white
// change left border line to white
self.chtChart.leftAxis.axisLineColor = UIColor.white

// change values from decimal to int on left axis
let fmt = NumberFormatter()
fmt.numberStyle = .decimal
fmt.maximumFractionDigits = 0
fmt.groupingSeparator = ","
fmt.decimalSeparator = "."
self.chtChart.leftAxis.valueFormatter = DefaultAxisValueFormatter(formatter: fmt)

self.chtChart.data = LineChartData(dataSets: [set_a])

正如你所看到的，我的图表没有底部边框，我也不能改变图表内部网格线的颜色（我想把它改为白色）。我试着执行以下命令，但没有任何变化：

self.chtChart.xAxis.axisLineColor = UIColor.white
self.chtChart.borderColor = UIColor.white
self.chtChart.xAxis.gridColor = UIColor.white