基于 NSData 子集的 Swift NSData 字符串转换

Question

情况

我正在处理中间有一个字符串编码的二进制数据。我想要做的是提取这个字符串，以便我可以“设置”和“获取”它。我想出了一个看起来有点时髦的方法（实际上是 3 个选项）。我已经包含了一个游乐场代码，您可以查看它。

我想知道是否有比我想出的“更好”的方法来处理这些数据。更好意味着更高效或更清晰的代码。

要读取数据，我执行以下操作 -

1. 通过将NSMutableData 转换为UnsafeMutablePoitner<UInt8> 来生成var rawData
2. 从rawData.mutableBytes 创建var ptr : UnsafeMutablePointer<UInt8>
3. 从第一个两个变量的组合中创建 UnsafeMutableBufferPointer<UInt8> 类型的数组 bytes
4. 创建一个新数组，仅由包含字符串bytes[19] - bytes[26] 的字节组成
5. 将此数组提取为字符串

然后设置变量我有 3 种方法，但我认为我会使用的方法是 1. 新建一串8串 2.创建[UInt8]字符串的字符数组 3.循环遍历新数组中的每个字节，并将bytes数组中字节的值设置为有问题的值

我假设有某种方法可以直接使用“父”字节数组，而不是制作子数组来使用。操场代码如下。我正在寻找一种更清洁的方法来做到这一点，也许没有。

谢谢

游乐场代码

import Cocoa
//import AppKit



///This is the raw data
var testBytes : [UInt8] = [0x14, 0x00, 0xAB, 0x45, 0x49, 0x1F, 0xEF, 0x15, 0xA8, 0x89, 0x78, 0x0F, 0x09, 0xA9, 0x07, 0xB0, 0x01, 0x20, 0x01, 0x4E, 0x38, 0x32, 0x35, 0x56, 0x20, 0x20, 0x20, 0x00]

///Convert into msgData
var msgData = NSMutableData(bytes: testBytes, length: testBytes.count)


// Store raw data into a byte array for messing with
var rawData: NSMutableData = NSMutableData(data: msgData)
var ptr: UnsafeMutablePointer<UInt8> = UnsafeMutablePointer<UInt8>(rawData.mutableBytes)
var bytes : UnsafeMutableBufferPointer<UInt8> = UnsafeMutableBufferPointer<UInt8>(start: ptr, count: rawData.length)


// Extract Callsign from the data stream
var callsignArray : [UInt8] = [bytes[19], bytes[20], bytes[21], bytes[22], bytes[23], bytes[24], bytes[25], bytes[26]]
var callsignString = NSString(bytes: callsignArray, length: callsignArray.count, encoding: NSUTF8StringEncoding)
let callsignString0 = callsignString!
println(callsignArray)
println("1. -- Initial Callsign [\(callsignString0)]")


//OPTION #1
// Edit Callsgin Array Directly (sketchy)
// And manually copy the bytes back into the base array
callsignArray[0] = 97
callsignArray[1] = 98
callsignArray[2] = 99
callsignArray[3] = 100

println(callsignArray)

// Write the new "bytes" back into the main array - there must be a better way
for (var i = 0; i <= 7; i++) {
    bytes[19+i] = callsignArray[i]
}

let callsign1 = NSString(bytes: callsignArray, length: callsignArray.count, encoding: NSUTF8StringEncoding)!

println("2. -- Modification of Bytes [\(callsign1)]")

//Option 3 - Go from String to Bytes

let callsign3 = "AABCDEF "
var buf = [UInt8](callsign3.utf8)

for (var i = 0; i <= 7; i++) {
    bytes[19+i] = buf[i]
}
println(rawData)

callsignArray = [bytes[19], bytes[20], bytes[21], bytes[22], bytes[23], bytes[24], bytes[25], bytes[26]]
callsignString = NSString(bytes: callsignArray, length: callsignArray.count, encoding: NSUTF8StringEncoding)

Answer 1

NSMutableData 具有提取和替换子范围的方法：

// Get: 
let subData = msgData.subdataWithRange(NSMakeRange(19, 8))
let string = NSString(data: subData, encoding: NSUTF8StringEncoding)

// Set:
let newString = "AABCDEF "
let newData = newString.dataUsingEncoding(NSUTF8StringEncoding)!
msgData.replaceBytesInRange(NSMakeRange(19, 8), withBytes: newData.bytes, length: newData.length)

也可以直接对[UInt8]数组进行操作：

// Get:
let string = testBytes.withUnsafeBufferPointer {
    NSString(bytes: UnsafePointer($0.baseAddress + 19), length: 8, encoding: NSUTF8StringEncoding)
}

// Set:
testBytes.replaceRange(19 ... 26, with: Array(newString.utf8))