从Swift 4（Xcode 9）开始，Swift标准库提供了在Swift字符串范围（Range<String.Index>）和NSString范围（NSRange）之间进行转换的方法。例：
let str = "a👿b🇩🇪c"
let r1 = str.range(of: "🇩🇪")!
// String range to NSRange:
let n1 = NSRange(r1, in: str)
print((str as NSString).substring(with: n1)) // 🇩🇪
// NSRange back to String range:
let r2 = Range(n1, in: str)!
print(str[r2]) // 🇩🇪
因此，现在可以按以下方式完成文本字段委托方法中的文本替换：
func textField(_ textField: UITextField,
shouldChangeCharactersIn range: NSRange,
replacementString string: String) -> Bool {
if let oldString = textField.text {
let newString = oldString.replacingCharacters(in: Range(range, in: oldString)!,
with: string)
// ...
}
// ...
}
（Swift 3和更早版本的旧答案：）
从Swift 1.2开始，String.Index具有初始化程序
init?(_ utf16Index: UTF16Index, within characters: String)
它可以用于转换NSRange到Range<String.Index>正确（包括表情符号，区域或指标的其他扩展字形簇的所有情况下），没有中间转化为NSString：
extension String {
func rangeFromNSRange(nsRange : NSRange) -> Range<String.Index>? {
let from16 = advance(utf16.startIndex, nsRange.location, utf16.endIndex)
let to16 = advance(from16, nsRange.length, utf16.endIndex)
if let from = String.Index(from16, within: self),
let to = String.Index(to16, within: self) {
return from ..< to
}
return nil
}
}
此方法返回一个可选的字符串范围，因为并非所有NSRanges都对给定的Swift字符串有效。
UITextFieldDelegate然后可以将委托方法编写为
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
if let swRange = textField.text.rangeFromNSRange(range) {
let newString = textField.text.stringByReplacingCharactersInRange(swRange, withString: string)
// ...
}
return true
}
逆转换是
extension String {
func NSRangeFromRange(range : Range<String.Index>) -> NSRange {
let utf16view = self.utf16
let from = String.UTF16View.Index(range.startIndex, within: utf16view)
let to = String.UTF16View.Index(range.endIndex, within: utf16view)
return NSMakeRange(from - utf16view.startIndex, to - from)
}
}
一个简单的测试：
let str = "a👿b🇩🇪c"
let r1 = str.rangeOfString("🇩🇪")!
// String range to NSRange:
let n1 = str.NSRangeFromRange(r1)
println((str as NSString).substringWithRange(n1)) // 🇩🇪
// NSRange back to String range:
let r2 = str.rangeFromNSRange(n1)!
println(str.substringWithRange(r2)) // 🇩🇪
Swift 2更新：
rangeFromNSRange()Serhii Yakovenko已在此答案中给出了Swift 2版本，出于完整性考虑，我在此包括它：
extension String {
func rangeFromNSRange(nsRange : NSRange) -> Range<String.Index>? {
let from16 = utf16.startIndex.advancedBy(nsRange.location, limit: utf16.endIndex)
let to16 = from16.advancedBy(nsRange.length, limit: utf16.endIndex)
if let from = String.Index(from16, within: self),
let to = String.Index(to16, within: self) {
return from ..< to
}
return nil
}
}
的Swift 2版本NSRangeFromRange()是
extension String {
func NSRangeFromRange(range : Range<String.Index>) -> NSRange {
let utf16view = self.utf16
let from = String.UTF16View.Index(range.startIndex, within: utf16view)
let to = String.UTF16View.Index(range.endIndex, within: utf16view)
return NSMakeRange(utf16view.startIndex.distanceTo(from), from.distanceTo(to))
}
}
Swift 3（Xcode 8）更新：
extension String {
func nsRange(from range: Range<String.Index>) -> NSRange {
let from = range.lowerBound.samePosition(in: utf16)
let to = range.upperBound.samePosition(in: utf16)
return NSRange(location: utf16.distance(from: utf16.startIndex, to: from),
length: utf16.distance(from: from, to: to))
}
}
extension String {
func range(from nsRange: NSRange) -> Range<String.Index>? {
guard
let from16 = utf16.index(utf16.startIndex, offsetBy: nsRange.location, limitedBy: utf16.endIndex),
let to16 = utf16.index(utf16.startIndex, offsetBy: nsRange.location + nsRange.length, limitedBy: utf16.endIndex),
let from = from16.samePosition(in: self),
let to = to16.samePosition(in: self)
else { return nil }
return from ..< to
}
}
例：
let str = "a👿b🇩🇪c"
let r1 = str.range(of: "🇩🇪")!
// String range to NSRange:
let n1 = str.nsRange(from: r1)
print((str as NSString).substring(with: n1)) // 🇩🇪
// NSRange back to String range:
let r2 = str.range(from: n1)!
print(str.substring(with: r2)) // 🇩🇪
