How to configure DateFormatter to capture microseconds

Question

iOS Date() returns date with at least microsecond precision.
I checked this statement by calling Date().timeIntervalSince1970 which results in

Answer 1

The resolution of (NS)DateFormatter is limited to milliseconds, compare NSDateFormatter milliseconds bug. A possible solution is to retrieve all date components (up to nanoseconds) as numbers and do a custom string formatting. The date formatter can still be used for the timezone string.

Example:

let date = Date(timeIntervalSince1970: 1490891661.074981)

let formatter = DateFormatter()
formatter.dateFormat = "ZZZZZ"
let tzString = formatter.string(from: date)

let cal = Calendar.current
let comps = cal.dateComponents([.year, .month, .day, .hour, .minute, .second, .nanosecond],
                               from: date)
let microSeconds = lrint(Double(comps.nanosecond!)/1000) // Divide by 1000 and round

let formatted = String(format: "%04ld-%02ld-%02ldT%02ld:%02ld:%02ld.%06ld",
                       comps.year!, comps.month!, comps.day!,
                       comps.hour!, comps.minute!, comps.second!,
                       microSeconds) + tzString

print(formatted) // 2017-03-30T18:34:21.074981+02:00