let commandsToPrint: NSData = ...
 
// Create char array with the required size:
var dataToSentToPrinter = [CUnsignedChar](count: commandsToPrint.length,repeatedValue: 0)
 
// Fill with bytes from NSData object:
commandsToPrint.getBytes(&dataToSentToPrinter,length: sizeofValue(dataToSentToPrinter))

更新：实际上你根本不需要复制数据(两者都没有)
Objective-C代码也不在Swift中).有一个指向数据的指针就足够了.
所以你的代码看起来像这样(比较
Error (“‘()’ is not identical to ‘UInt8′”) writing NSData bytes to NSOutputStream using the write function in Swift
对于类似的问题)：

let dataToSentToPrinter = UnsafePointer<CUnsignedChar>(commandsToPrint.bytes)
let commandSize = commandsToPrint.length
var totalAmountWritten = 0
 
while totalAmountWritten < commandSize {
    let remaining = commandSize - totalAmountWritten
    let amountWritten = starPort.writePort(dataToSentToPrinter,totalAmountWritten,remaining)
    totalAmountWritten += amountWritten
    // ...
}