swift - 在Swift 4中按功能转换UTF16View.Index高级

因此，在Swift 3中，我使用此函数将代表Hexa数据的String转换为Data类型：

extension String {

public func fromHexStringtoData() -> Data? {
    func convertToUInt8(u: UInt16) -> UInt8? {
        switch(u) {
        case 0x30 ... 0x39:
            return UInt8(u - 0x30)
        case 0x41 ... 0x46:
            return UInt8(u - 0x41 + 10)
        case 0x61 ... 0x66:
            return UInt8(u - 0x61 + 10)
        default:
            return nil
        }
    }

    let utf16 = self.utf16
    guard let data = NSMutableData(capacity: utf16.count/2) else { return nil }
    var i = utf16.startIndex
    while i != utf16.endIndex {
        guard let hi = convertToUInt8(u: utf16[i]) else { return nil }

        //Need to convert following line to Swift 4
        guard let lo = convertToUInt8(u: utf16[i.advanced(by: 1)]) else { return nil }

        var value = hi << 4 + lo
        data.append(&value, length: 1)

        //Need to convert following line to Swift 4
        i = i.advanced(by: 2)
    }
    return data as Data
}

}

如何以最佳方式转换advanced(by: n)？

最佳答案

您必须像这样使用：

extension String {
    public func fromHexStringtoData() -> Data? {
        func convertToUInt8(u: UInt16) -> UInt8? {
            switch(u) {
            case 0x30 ... 0x39:
                return UInt8(u - 0x30)
            case 0x41 ... 0x46:
                return UInt8(u - 0x41 + 10)
            case 0x61 ... 0x66:
                return UInt8(u - 0x61 + 10)
            default:
                return nil
            }
        }

        let utf16 = self.utf16
        guard let data = NSMutableData(capacity: utf16.count/2) else { return nil }
        var i = utf16.startIndex
        while i != utf16.endIndex {
            guard let hi = convertToUInt8(u: utf16[i]) else { return nil }

            //changed to Swift 4
            guard let lo = convertToUInt8(u: utf16[utf16.index(i, offsetBy: 1)]) else { return nil }

            var value = hi << 4 + lo
            data.append(&value, length: 1)

            //changed to Swift 4
            i = utf16.index(i, offsetBy: 2)
        }
        return data as Data
    }
}