如何在图表 ios 中设置自定义 x 轴 0 标签

Question

I am using Charts by Daniel Gindi

How can I set a String 0 label on x Axis? I want it to show "Now" instead of a Date type. I've seen the function that helps to format one particular label only, but I can't get how it works. Moreover, I haven't seen any examples of it. So, how does getFormattedLabel(index: Int) work? This is what I need my xAxis to look like:

Thank you!

Answer 1

You can set your xAxis.valueFormatter to your own custom class and then return now when your x value is 0. Like:

class ChartValueFormatter: NSObject, IAxisValueFormatter {

    func stringForValue(_ value: Double, axis: AxisBase?) -> String {

        if value == 0 {

            return "Now"
        }

        let dateFormatter = DateFormatter()
        dateFormatter.setLocalizedDateFormatFromTemplate("dd MMM")
        dateFormatter.locale = .current

        let date = Date(timeIntervalSince1970: value)

        return dateFormatter.string(from: date)
    }
}

For this to work you need to sort your values based on date and then set then now value timestamp to zero.

Answer 2

It took a while to figure out, but I found a great tutorial on Medium by Spencer Mandrusiak

I needed to make the first label of a String type and all the others should still be Date types. What I did:

• Created an X axis formatting class.
• Added an enum with only one label
• When returning a value, I return time if there are no custom labels left.

This solution works well for me!

class ChartXAxisFormatter: NSObject, IAxisValueFormatter {

    enum CustomLabel: Int {
        case firstLabel

        var label: String {
            switch self {
            case .firstLabel: return "Now"                
                }
            }
        }

 func stringForValue(_ value: Double, axis: AxisBase?) -> String {
            let dateFormatterPrint = DateFormatter()
            dateFormatterPrint.dateFormat = "hh:mm"

            let date = Date(timeIntervalSince1970: value)
            let time = dateFormatterPrint.string(from: date)

            let intVal = Int(value)
            let customLabel = CustomLabel(rawValue: intVal)
            return customLabel?.label ?? "\(time)"


    }
}

Answer 3

This is a snippet that helps me convert an X axis into timeline and also make the last label on the chart of a String type.

index == count - 2 was used because the label count on X axis was set to 3 by force:

chart.xAxis.setLabelCount(3, force: true)
chart.xAxis.avoidFirstLastClippingEnabled = false
chart.xAxis.forceLabelsEnabled = true

class ChartXAxisFormatter: NSObject, IAxisValueFormatter {

    func stringForValue(_ value: Double, axis: AxisBase?) -> String {

        if let index = axis?.entries.firstIndex(of: value), let count = axis?.entries.count  , index == count - 2 {
            return "Now"
        }

        let dateFormatterPrint = DateFormatter()
        dateFormatterPrint.dateFormat = "HH:mm:ss"

        let date = Date(timeIntervalSince1970: value)
        let time = dateFormatterPrint.string(from: date)

            return time
      }
}