在swift中使用NSData

Question

所以我已经想出如何在swift中提取NSData但是我对设置它感到困惑:

var testBytes : [Byte] = [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]

var msgData = NSData(bytes: testBytes, length: testBytes.count)

println("\(msgData)")


var length : Int = testBytes.count

var out: NSInteger = 0

let ptr = UnsafePointer<UInt8>(msgData.bytes)
var bytes = UnsafeBufferPointer<UInt8>(start: ptr, count: 28)

因此,如果我想访问一个特定的字节,我可以用以下内容获取它:

let targetAddress = UInt32(bytes[2]) << 16 |
    UInt32(bytes[3]) << 8 |
    UInt32(bytes[4]) << 0

现在说我想用以下内容设置一个值:

bytes[11] = UInt8(UInt32(bytes[11]) | 0x0FF)

我得到一个错误Cannot assign the result of this expression).我也试过用&bytes[11]它似乎也不会飞.

我假设这是因为数组使用不安全的缓冲区指针.是否有一个轻松的电话,我有一些如何掩饰,以使作业正常工作？

Answer 1

如果要修改从NSData 对象检索的字节,则应将字节复制到单独的数组中

var bytes = [UInt8](count: msgData.length, repeatedValue: 0)
msgData.getBytes(&bytes, length: bytes.count)

bytes[11] = UInt8(UInt32(bytes[11]) | 0x0FF)

NSData 是一个不可变的对象,和

let ptr = UnsafePointer<UInt8>(msgData.bytes)

是一个常量指针,因此您不能修改指向的数据.

或者,从一开始就使用可变数据对象:

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

let ptr = UnsafeMutablePointer<UInt8>(msgData.mutableBytes)
var bytes = UnsafeMutableBufferPointer<UInt8>(start: ptr, count: msgData.length)

bytes[11] = UInt8(UInt32(bytes[11]) | 0x0FF)

注意使用msgData.mutableBytes而不是msgData.bytes.这将msgData直接修改数据.