Objective C to Swift code conversion, can't seem to treat bytes correctly in Swift

Question

I\'m working on a simple Swift bluetooth heart rate monitor iOS App. I found this great tutorial which has objective C code. I\'ve converted it to Swift and I\'m getting data fr

Answer 1

const uint8_t *reportData = [data bytes];

translates to

let reportData = UnsafePointer<UInt8>(data.bytes)

Then reportData has the type UnsafePointer<UInt8> and you can access it as in (Objective-)C:

if (reportData[0] & 0x01) == 0 { ... }

Next,

bpm = reportData[1];

is almost identical in Swift. You have to convert explicitly from UInt8 to UInt16 because – unlike (Objective-)C – Swift does not implicitly convert between types:

bpm = UInt16(reportData[1]) 

Putting it together:

func getHeartBPMData(characteristic: CBCharacteristic!) {
    let data = characteristic.value
    let reportData = UnsafePointer<UInt8>(data.bytes)
    var bpm : UInt16
    if (reportData[0] & 0x01) == 0 {
        bpm = UInt16(reportData[1])
    } else {
        bpm = UnsafePointer<UInt16>(reportData + 1)[0]
        bpm = CFSwapInt16LittleToHost(bpm)
    }

    // ...
}

Note that most of your variables can be declared as constants with let, instead of var. Instead of

bpm = CFSwapInt16LittleToHost(bpm)

you can alternatively use the littleEndian: constructor which is available for all integer types:

bpm = UInt16(littleEndian: bpm)

---

Update for Swift 3/4:

func getHeartBPMData(characteristic: CBCharacteristic) {
    guard  let reportData = characteristic.value else {
        return 
    }

    let bpm : UInt16
    if (reportData[0] & 0x01) == 0 {
        bpm = UInt16(reportData[1])
    } else {
        bpm = UInt16(littleEndian: reportData.subdata(in: 1..<3).withUnsafeBytes { $0.pointee } )
    }

    // ...
}