ios Charts 3.0 - Align x labels (dates) with plots

Question

I am having a hard time to migrate library Charts (from Daniel Gindi) from version 2 (Swift 2.3) to 3 (Swift 3).

Basically, I can\'t have the x labels (dates) aligne

Answer 1

here is the Solution of xValuesNumberFormatter

let xValuesFormatter = DateFormatter()
    xValuesFormatter.dateFormat = "MM/dd"
let xValuesNumberFormatter = ChartXAxisFormatter(referenceTimeInterval: referenceTimeInterval, dateFormatter: xValuesFormatter)
    xValuesNumberFormatter.dateFormatter = xValuesFormatter // e.g. "wed 26"
    xAxis.valueFormatter = xValuesNumberFormatter

Answer 2

OK, got it!

You've got to define a reference time Interval (the "0" for the x axis). And then calculate the additional time interval for each x value.

The ChartXAxisFormatter becomes:

import Foundation
import Charts

class ChartXAxisFormatter: NSObject {
    fileprivate var dateFormatter: DateFormatter?
    fileprivate var referenceTimeInterval: TimeInterval?

    convenience init(referenceTimeInterval: TimeInterval, dateFormatter: DateFormatter) {
        self.init()
        self.referenceTimeInterval = referenceTimeInterval
        self.dateFormatter = dateFormatter
    }
}


extension ChartXAxisFormatter: IAxisValueFormatter {

    func stringForValue(_ value: Double, axis: AxisBase?) -> String {
        guard let dateFormatter = dateFormatter,
        let referenceTimeInterval = referenceTimeInterval
        else {
            return ""
        }

        let date = Date(timeIntervalSince1970: value * 3600 * 24 + referenceTimeInterval)
        return dateFormatter.string(from: date)
    }

}

And, then, when I create my data entries, it works like so:

// (objects is defined as an array of struct with date and value)

// Define the reference time interval
var referenceTimeInterval: TimeInterval = 0
if let minTimeInterval = (objects.map { $0.date.timeIntervalSince1970 }).min() {
        referenceTimeInterval = minTimeInterval
    }


    // Define chart xValues formatter
    let formatter = DateFormatter()
    formatter.dateStyle = .short
    formatter.timeStyle = .none
    formatter.locale = Locale.current

    let xValuesNumberFormatter = ChartXAxisFormatter(referenceTimeInterval: referenceTimeInterval, dateFormatter: formatter)



    // Define chart entries
    var entries = [ChartDataEntry]()
    for object in objects {
        let timeInterval = object.date.timeIntervalSince1970
        let xValue = (timeInterval - referenceTimeInterval) / (3600 * 24)

        let yValue = object.value
        let entry = ChartDataEntry(x: xValue, y: yValue)
        entries.append(entry)
    }

// Pass these entries and the formatter to the Chart ...

The result is much nicer (I removed cubic by the way):

Answer 3

If you exactly know how many labels you need in the x-axis,you can write this code to solve it.For example,If I need seven labels to appear on the x-axis,Then this should be enough.The reason is the chart library is not properly calculating the intervals between the two x-axis points and hence the plot-label mismatch.When we force the library to plot against the given number of labels,The issue seems to be gone.

 let xAxis = chart.xAxis
 xAxis.centerAxisLabelsEnabled = false
 xAxis.setLabelCount(7, force: true) //enter the number of labels here

Answer 4

I solved this issue using this answer https://stackoverflow.com/a/44554613/2087608

I suspected that these offsets come from adjusting X axis value to a specific time of the day in my case

Here is my code

for i in 0..<valuesViewModel.entries.count {
  let dataEntry = ChartDataEntry(x: roundDate(date: valuesViewModel.entries[i].date).timeIntervalSince1970, y: valuesViewModel.entries[i].value)
  dataEntries.append(dataEntry)
}



func roundDate(date: Date) -> Date {
  var comp: DateComponents = Calendar.current.dateComponents([.year, .month, .day], from: date)
  comp.timeZone = TimeZone(abbreviation: "UTC")!
  let truncated = Calendar.current.date(from: comp)!
  return truncated
}