Values on X axis issue

[milosmilakovic-oviva]

I use ScatterChart. On the x axis labels should be hours (00:00, 06:00, 12:00, 18:00). But, If I put minimum = 0 and maximum = 1440 (minutes in day) and and label count to 5 I get graph like this:

If I set labelCount to 4, labels on xAxis are: 00:00, 06:40 (400), 13:20 (800), 20:00 (1200).
If labelCount = 3 axis are 00:00, 08:20 (500), 16:40 (1000)

This is my setup:
vwChart.xAxis.axisMinimum = 0 vwChart.xAxis.axisMaximum = 1440 vwChart.setVisibleXRangeMaximum(1440) vwChart.setVisibleXRangeMinimum(1440) vwChart.xAxis.labelCount = 4 // 5, 6, 3, 2

Is there a way to specify interval between labels, so I can display each 6h?

[liuxuan30]

check computeAxisValues(), where it generate the x axis labels. You can override it with your own

[JCMcLovin]

@liuxuan30 - does the demo project have an example that overrides computeAxisValues()? I can't seem to find one that does.

[liuxuan30]

no, it's default one. The logic is simple, just do math or none

[tianli91]

So when we need to manually override the computeAxisValues() for the XAxisRenderer. Here is an example @JCMcLovin :

class NonUniformXAxisRenderer: XAxisRenderer {
    override func computeAxisValues(min: Double, max: Double) {
        super.computeAxisValues(min: min, max: max)
 
        guard let axis = self.axis else { return }
         
        let labelCount = axis.labelCount
        let interval = 86400000.0
         
       // Ensure stops contains at least n elements.
        axis.entries.removeAll(keepingCapacity: true)
        axis.entries.reserveCapacity(labelCount)
        axis.entries.append(min)
        var v = min + 26423301
        
        for _ in 0 ..< labelCount - 2
        {
            axis.entries.append(v)
            v += interval
        }
        axis.entries.append(max)
         
    }
}

let transformer = chartView.getTransformer(forAxis:.left)
let viewPortHandler = chartView.xAxisRenderer.viewPortHandler
chartView.xAxisRenderer = NonUniformXAxisRenderer(viewPortHandler: viewPortHandler, xAxis: chartView.xAxis, transformer: transformer)

Take note you cannot use your own transformer and viewPortHandler instance.
This matrix transforms the dataset x values to the pixels on screen. the default transformer re-calculate the mapping matrix when viewPort changes

ChartXAxis Value Not Displayed
So first check xAxis.entries in computeAxisValues(), and then drawLabels()
You can try debug xAxis.drawLabels() at if viewPortHandler.isInBoundsX(position.x) to see if it meets the condition.

@liuxuan30 the logic is simple but it did take me hours to figure out why the axis label not showing. I used my own transformer and viewPortHandler instance and read all the related source code to know why it does not work.