无法快速将 NSData 转换为 NSString [英] Can't convert NSData to NSString in swift

问题描述

这是我的职责.首先 println 将正确的哈希打印到控制台，但在下一行程序崩溃.你能帮助我吗?

This is my function. First println print correct hash to console but in the next row program crashes. Can you help me?

func sha256(string: NSString) -> NSString {
    var data : NSData! = string.dataUsingEncoding(NSUTF8StringEncoding)
    var hash = [UInt8](count: Int(CC_SHA256_DIGEST_LENGTH), repeatedValue: 0)
    CC_SHA256(data.bytes, CC_LONG(data.length), &hash)
    let res = NSData(bytes: hash, length: Int(CC_SHA256_DIGEST_LENGTH))
    println(res)
    let resstr = NSString(data: res, encoding: NSUTF8StringEncoding)
    println(resstr)
    return resstr
}

推荐答案

let resstr = NSString(data: res, encoding: NSUTF8StringEncoding)

返回 nil 如果数据不代表有效的 UTF-8 序列(这很有可能).然后下面的 println() 崩溃了.

returns nil if the data does not represent a valid UTF-8 sequence (which is very likely). Then the following println() crashes.

任意二进制数据的一种可能的字符串表示是一个十六进制字符串或一个 Base-64 编码的字符串.

A possible string representation for arbitrary binary data would be a hex string or a Base-64 encoded string.

Base-64 编码的字符串可以简单地通过

let resstr = res.base64EncodedStringWithOptions(nil)

(据我所知)没有将二进制数据转换为十六进制字符串的内置方法.Swift 中的一个可能实现(受到许多可用的 Objective-C 解决方案的启发)是

There is (as far as I know) no built-in method to convert binary data to a hex string. A possible implementation in Swift (inspired by the lots of available Objective-C solutions) is

extension NSData {
    func hexString() -> NSString {
        var str = NSMutableString()
        let bytes = UnsafeBufferPointer<UInt8>(start: UnsafePointer(self.bytes), count:self.length)
        for byte in bytes {
            str.appendFormat("%02hhx", byte)
        }
        return str
    }
}

但是您可以将其直接集成到您的哈希方法中，而无需使用中间 NSData 对象:

But you could integrate that into your hash method directly, without using an intermediate NSData object:

func sha256(string: NSString) -> NSString {
    let data = string.dataUsingEncoding(NSUTF8StringEncoding)!
    var hash = [UInt8](count: Int(CC_SHA256_DIGEST_LENGTH), repeatedValue: 0)
    CC_SHA256(data.bytes, CC_LONG(data.length), &hash)
    let resstr = NSMutableString()
    for byte in hash {
        resstr.appendFormat("%02hhx", byte)
    }
    return resstr
}

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