fix for crash when interval is NaN

[pingd]

After clearing a working chart and then adding new data (dataset), the chart crashes in AxisRendererBase.swift line 125 with "Double value cannot be converted to Int because it is either infinite or NaN". The reason for that is "min" and "max" are NaN (because the Transformer._matrixValueToPx is somewhat invalid(?), why does it happen?).

The issue is referenced here: https://stackoverflow.com/questions/45496912/how-to-clear-a-chart-and-then-add-data-to-it-in-swift-3-using-chartview-clear and here: #2168 (josman185hotm's comment from 17 Jun).

[codecov-io]

Codecov Report

Merging #2804 into master will decrease coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #2804     +/-   ##
=========================================
- Coverage   19.64%   19.54%   -0.1%     
=========================================
  Files         113      113             
  Lines       13791    13878     +87     
=========================================
+ Hits         2709     2713      +4     
- Misses      11082    11165     +83

Impacted Files	Coverage Δ
Source/Charts/Renderers/AxisRendererBase.swift	59.02% <100%> (ø)	⬆️
...s/Renderers/Scatter/ChevronDownShapeRenderer.swift	0% <0%> (ø)	⬆️
...rts/Renderers/Scatter/ChevronUpShapeRenderer.swift	0% <0%> (ø)	⬆️
Source/Charts/Highlight/Highlight.swift	0% <0%> (ø)	⬆️
...Charts/Renderers/Scatter/CircleShapeRenderer.swift	0% <0%> (ø)	⬆️
...arts/Renderers/Scatter/TriangleShapeRenderer.swift	0% <0%> (ø)	⬆️
.../Charts/Renderers/Scatter/CrossShapeRenderer.swift	0% <0%> (ø)	⬆️
Source/Charts/Filters/DataApproximator.swift	0% <0%> (ø)	⬆️
...urce/Charts/Renderers/Scatter/XShapeRenderer.swift	0% <0%> (ø)	⬆️
...Charts/Renderers/Scatter/SquareShapeRenderer.swift	0% <0%> (ø)	⬆️
... and 2 more

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[liuxuan30]

#2377 is my thought to fix. Have you checked it's the reason why you saw NaN on your side?

[liuxuan30]

I looked at your change again, it seems not the same thing. range should not be NaN at all.
Do you have the exact values that causes NaN? We'd like to investigate.

In the code, min/max are coming from:

    @objc open func computeAxis(min: Double, max: Double, inverted: Bool)
    {
        var min = min, max = max
        
        if let transformer = self.transformer
        {
            // calculate the starting and entry point of the y-labels (depending on zoom / contentrect bounds)
            if let viewPortHandler = viewPortHandler
            {
                if viewPortHandler.contentWidth > 10.0 && !viewPortHandler.isFullyZoomedOutY
                {
                    let p1 = transformer.valueForTouchPoint(CGPoint(x: viewPortHandler.contentLeft, y: viewPortHandler.contentTop))
                    let p2 = transformer.valueForTouchPoint(CGPoint(x: viewPortHandler.contentLeft, y: viewPortHandler.contentBottom))
                    
                    if !inverted
                    {
                        min = Double(p2.y)
                        max = Double(p1.y)
                    }
                    else
                    {
                        min = Double(p1.y)
                        max = Double(p2.y)
                    }
                }
            }
        }
        
        computeAxisValues(min: min, max: max)
    }

which basically take the contentRect coordinates to calculate. If this goes wrong, the chart setup is a mess in the first place then, which should not happen at all.

Adding a NaN check is the last resort to prevent crash, but we don't want to silent the crash first, it will be more difficult to notice.

[liuxuan30]

please open an issue to track NaN crash for your case, with details or values that causes NaN, thanks.

[pingd]

I am not able to open an issue with actual code for about two weeks, as I am away. However, it happens roughly when you do something like in the SO issue.

In my case, the steps go like this:

1. Set up a CandleStickChartView.
2. Create a new CandleChartData with no underlaying dataset. Set chart.data to it.
3. Create an empty CandleChartDataSet. Add it to chart data.
4. Add values to chart. (At this point everything works correctly, the chart is displayed, the values can be update real time and so on).
5. When I need to switch to another ViewController, I stop my data updates and clear chart.
6. When I go back to a ViewController with chart, I repeat the process from step 2. After adding values and calling notifyDataSetChanged(), I get "Double value cannot be converted to Int because it is either infinite or NaN" on line 125 in AxisRendererBase.

I will open an actual issue with code once I am back.

[maciejtrybilo]

+1 Having the same issue.

[liuxuan30]

I logged the reason in #2845 why closing this.

[SeRG1k17]

@liuxuan30
I think this will be useful to many.
And, it is required to use only a ChartData class, because any subclass also calls crash( < ios11).

override var data: ChartData? {
        get { return super.data }
        set {
            guard let newData = newValue, newData.entryCount > 0 else {
                super.data = ChartData(dataSet: ChartDataSet(values: [ChartDataEntry()]))
                return
            }
            
            super.data = newData
            notifyDataSetChanged()
        }
    }

[atalayasa]

Hello @SeRG1k17 I had same issue too but no other solutions worked for me where should I put your code ? Thanks

[atalayasa]

I have solved the issue using following answer https://stackoverflow.com/questions/45496912/how-to-clear-a-chart-and-then-add-data-to-it-in-swift-3-using-chartview-clear