swift 3；范围 'Out of bounds'

Question

我刚刚将 Xcode 更新到 8.0 beta 2 和 swift 3.0。从 swift 2.3 更新后，我遇到了很多错误。

我有一个字符串扩展，它将“self”字符串中的范围转换为 NSRange:

extension String {

    func NSRangeFromRange(_ range : Range<String.Index>) -> NSRange {

        let utf16view = self.utf16
        let from = String.UTF16View.Index(range.lowerBound, within: utf16view)
        let to = String.UTF16View.Index(range.upperBound, within: utf16view)

        print("to: \(to) from: \(from)")
        print(self.characters.count)

        return NSMakeRange(utf16view.startIndex.distance(to: from), from.distance(to: to))
    //    return NSMakeRange(0, 0)    // <-- removes exception
    }
}

执行 NSMakeRange 时出现错误:

Terminating app due to uncaught exception 'NSRangeException', reason: 'NSMutableRLEArray objectAtIndex:effectiveRange:: Out of bounds'

当我打印 to- 和 from-index 时，我得到:

to: Index(_offset: 194) from: Index(_offset: 181)

字符串的字符数是 210，这似乎是正确的。

所以，我不明白为什么它告诉我索引超出范围，当它们小于总数时。

在我更新到 swift 3 之前，这条线运行良好。当时它看起来像这样:

return NSMakeRange(utf16view.startIndex.distanceTo(from), from.distanceTo(to))

自动转换器没有将语法从 swift 2.3 更新到 3.0，我自己做了。

有什么线索吗？

Answer 1

在 Swift 3 中，“Collections move their index”，参见 A New Model for Collections and Indices关于 Swift 演进。

在 Swift 2.2 中，advancedBy()和 distanceTo()方法是在索引上调用:

let u16 = "12345".utf16
let i1 = u16.startIndex.advancedBy(1)
let i2 = u16.startIndex.advancedBy(3)
let d = i1.distanceTo(i2)
print(d) // 2

这个方法在 Swift 3 中仍然存在，但给出了意想不到的结果，至少在字符集合上是这样:

let u16 = "12345".utf16
let i1 = u16.startIndex.advanced(by: 1)
let i2 = u16.startIndex.advanced(by: 3)
let d = i1.distance(to: i2)
print(d) // -2

正确的方法是使用 index()和 distance()方法 集合本身:

let u16 = "12345".utf16
let i1 = u16.index(u16.startIndex, offsetBy: 1)
let i2 = u16.index(u16.startIndex, offsetBy: 3)
let d = u16.distance(from: i1, to: i2)
print(d) // 2

应用于您的问题，这就是您可以转换 Range<String.Index>到对应的NSRange在 swift 3(从 https://stackoverflow.com/a/30404532/1187415 复制):

extension String {
    func nsRange(from range: Range<String.Index>) -> NSRange {
        let utf16view = self.utf16
        let from = range.lowerBound.samePosition(in: utf16view)
        let to = range.upperBound.samePosition(in: utf16view)
        return NSMakeRange(utf16view.distance(from: utf16view.startIndex, to: from),
                              utf16view.distance(from: from, to: to))
    }
}

为了完整起见，这是相反的转换

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(from16, offsetBy: nsRange.length, limitedBy: utf16.endIndex),
            let from = String.Index(from16, within: self),
            let to = String.Index(to16, within: self)
        else { return nil }
        return from ..< to
    }
}