ChartYAxis valueFormatter NSFormatter instead of NSNumberFormatter

[eliotfowler]

Once you have the data you need to place the y-axis labels on the line in order, why do you need the value formatter be a NSNumberFormatter as opposed to just a NSFormatter. The reason I ask is I'm trying to plot times and I'd like to be able to show it in MM:SS format instead of minute.fraction format.

The same could be true with the labels placed above/below the data points.

[danielgindi]

Y values are number, hence NSNumberFormatter, which accepts numbers. If you want to print time, then subclass NSNumberFormatter, parse the time decimal and output a string.

[mathiasgithub]

It would be great to support other formatter types because subclassing NSNumberFormatter and overriding

 func stringFromNumber(number: NSNumber) -> String? 

is a bit awkward if you're creating a new formatter type in that function to for example parse dates.

[liuxuan30]

@mathiasgithub but y axis is meant to be numbers, right? I don't know if the y axis is about dates, how do you draw the charts? What's the meaning? Any examples?

[mathiasgithub]

@liuxuan30 here's one of the formatters I would love to be able to use:

    static var dateComponentsFormatter: NSDateComponentsFormatter {
        let dateComponentsFormatter = NSDateComponentsFormatter()
        dateComponentsFormatter.allowedUnits = [.Minute, .Second]
        dateComponentsFormatter.collapsesLargestUnit = true
        dateComponentsFormatter.zeroFormattingBehavior = .Pad
        return dateComponentsFormatter
    }

I use it to convert seconds (Int) to a string with the format MM:SS

I think it's useful to be able to represent the values on the y axis in any way you might want. NSNumberFormatter limits that.

NSDateComponentsFormatter inherits from NSFormatter

[liuxuan30]

I see. It will calculate the y axis range to determine how we draw the chart. We cannot change it to NSFormatter, since it does not provide a default implementation for converting from double values. We could provide one, but seems it requires a decent work on it, without a high priority. If you want this support, you are more than welcome to file a PR :)

[mathiasgithub]

Thank you! No problem, I understand. I’ll see what I can do with that PR

Cheers

On 14 Dec 2015, at 11:55, Xuan notifications@github.com wrote:

I see. It will calculate the y axis range to determine how we draw the chart. We cannot change it to NSFormatter, since it does not provide a default implementation for converting to double values. We could provide one, but seems like it requires a decent work on it, without a high priority. If you want this support, you are more than welcome to file a PR :)

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