How can I get a Decimal Tab Stop on iOS when NSTextTab on iOS doesn't offer that option?

Question

When developing for OS X, you have the option of specifying the DecimalTabStopType to get a tab stop on the decimal point of a column of numbers. However, this option isn't available in iOS - is there some way to achieve the same affect?

Answer 1

Currently there's a built-in support for decimal tab stops, see https://developer.apple.com/documentation/uikit/nstexttab/1535107-columnterminators

Can be used as follows

let paragraphStyle = NSMutableParagraphStyle()
let terms = NSTextTab.columnTerminators(for: NSLocale.current)
let tabStop0 = NSTextTab(textAlignment: .right, location: 100, options: 
[NSTabColumnTerminatorsAttributeName:terms])

Answer 2

With a little bit of effort, you can easily achieve the same effect on iOS. First, you add a Right tab stop. Then, you add a Left tab stop a very tiny bit to the right. [It appears that the tabStop array is sorted by their offset, so you cannot use exactly the same offset.]

let centerTab = NSTextTab(textAlignment: .Right, location: width - 100, options: [:])
let leftTab = NSTextTab(textAlignment: .Left, location: width - 100 + 0.001, options: [:])

When you have a plan number - no decimal point - you would append text of "value\t" - the value is aligned to the left of the first tab stop, then the tab character takes you to the next tab. If you have a string with a decimal point, split the string into two parts, and then pass the string "firstPart" + "\t + "." "secondPart".

let nString: String
if case let array = item.value.componentsSeparatedByString(".") where array.count == 2 {
   nString = array[0] + "\t." + array[1]
} else {
   nString = item.value + "\t"
}
// append nString

You can also use this to align numbers some of which are values and others which have trailing percent signs (using similar techniques).