range, and therefore interval, is NaN in computeAxisValues

[pingd]

For some reason min and max in computeAxis are NaN, which causes a problem with calculating range and interval in computeAxisValues (as referenced in my PR).

Here is a piece of code that breaks every time (after calling reloadDataTap).

class ViewController: UIViewController {

    @IBOutlet weak var chartView: CandleStickChartView!

    private let entries = [CandleChartDataEntry(x: 0, shadowH: 1.001, shadowL: 0.990, open: 0.999, close: 0.999), CandleChartDataEntry(x: 1, shadowH: 1.01, shadowL: 0.999, open: 0.997, close: 0.998), CandleChartDataEntry(x: 2, shadowH: 1.001, shadowL: 0.992, open: 1.002, close: 0.0989), CandleChartDataEntry(x: 3, shadowH: 1.0031, shadowL: 0.995, open: 1, close: 1.001), CandleChartDataEntry(x: 4, shadowH: 1.007, shadowL: 0.999, open: 0.997, close: 0.997)]
    private let entries2 = [CandleChartDataEntry(x: 5, shadowH: 1.001, shadowL: 0.990, open: 0.999, close: 0.999), CandleChartDataEntry(x: 6, shadowH: 1.001, shadowL: 0.990, open: 0.999, close: 0.999), CandleChartDataEntry(x: 7, shadowH: 1.001, shadowL: 0.990, open: 0.999, close: 0.999), CandleChartDataEntry(x: 8, shadowH: 1.001, shadowL: 0.990, open: 0.999, close: 0.999), CandleChartDataEntry(x: 94, shadowH: 1.001, shadowL: 0.990, open: 0.999, close: 0.999)]

    override func viewDidLoad() {
        super.viewDidLoad()
    
        setupChart()
    
        addEntries(entries: entries)
        addEntries(entries: entries2)
    }

    private func setupChart() {
        chartView.highlightPerDragEnabled = false
        chartView.doubleTapToZoomEnabled = false
        chartView.dragDecelerationEnabled = false
        chartView.pinchZoomEnabled = false
        chartView.scaleYEnabled = false
        chartView.scaleXEnabled = true
    
        chartView.chartDescription?.text = nil
        chartView.legend.enabled = false
    
        chartView.xAxis.spaceMin = 3.0
        chartView.xAxis.spaceMax = 5.0
        chartView.xAxis.setLabelCount(4, force: false)
    
        chartView.rightAxis.setLabelCount(7, force: false)
    
        chartView.leftAxis.enabled = false
    
        chartView.minOffset = 0
        chartView.setExtraOffsets(left: 0, top: 5, right: 0, bottom: 25)
    }

    private func createSet() -> CandleChartDataSet {
        let candleChartDataSet = CandleChartDataSet(values: nil, label: nil)
        candleChartDataSet.axisDependency = .right
        candleChartDataSet.drawIconsEnabled = false
        candleChartDataSet.drawValuesEnabled = false
    
        return candleChartDataSet
    }

    private func addEntries(entries: [CandleChartDataEntry]) {
        if chartView.data == nil {
            chartView.data = CandleChartData()
        }
    
        let data = chartView.candleData!
        
        var set = data.getDataSetByIndex(0)
        if set == nil {
            set = createSet()
            data.addDataSet(set)
        }
        
        for entry in entries {
            data.addEntry(entry, dataSetIndex: 0)
        }
        
        data.notifyDataChanged()
        
        chartView.notifyDataSetChanged()
        
        chartView.autoScaleMinMaxEnabled = true
        chartView.setVisibleXRange(minXRange: Double(5), maxXRange: Double(15))

        chartView.setNeedsDisplay()
    }

    @IBAction func reloadDataTap(_ sender: UIButton) {
        chartView.clear()
        addEntries(entries: entries)
    }
}

[liuxuan30]

You don't debug and walk through ChartsDemo very well, it's wrong calling chartView.data = CandleChartData() without any valid data, leading _xAxis._axisMinimum to be +inf and causes the matrix became a mess in the first place.

Never init an empty chart data because a lot of calculation involved in data setter. Another thing is data.notifyDataChanged() is not needed, chartView.notifyDataSetChanged() will do the job

I am going to close your PR as well, since we don't want to silent the mistakes people made or a true bug.

[pingd]

If initializing the chart with empty data is leading to problems, then perhaps a better design would be to either prevent doing so, or check if the data is empty before doing any calculations. I use the same logic in an Android app using MPAndroidChart library and have not run into that issue there.

[liuxuan30]

I admit. It's a bit tricky here. the data setter has been modified several times to avoid different issues.