[英]Objective C to Swift code conversion, can't seem to treat bytes correctly in Swift
我正在研究一款简单的Swift蓝牙心率监测器iOS App。 我发现这个很棒的教程有客观的C代码。 我已将它转换为Swift,我从心率监测器获取数据。 我的问题是我似乎无法正确访问和转换Swift中的字节数据。
这是Objective C代码:
// Instance method to get the heart rate BPM information
- (void) getHeartBPMData:(CBCharacteristic *)characteristic error:(NSError *)error
{
// Get the Heart Rate Monitor BPM
NSData *data = [characteristic value]; // 1
const uint8_t *reportData = [data bytes];
uint16_t bpm = 0;
if ((reportData[0] & 0x01) == 0) { // 2
// Retrieve the BPM value for the Heart Rate Monitor
bpm = reportData[1];
}
else {
bpm = CFSwapInt16LittleToHost(*(uint16_t *)(&reportData[1])); // 3
}
// Display the heart rate value to the UI if no error occurred
if( (characteristic.value) || !error ) { // 4
self.heartRate = bpm;
self.heartRateBPM.text = [NSString stringWithFormat:@"%i bpm", bpm];
self.heartRateBPM.font = [UIFont fontWithName:@"Futura-CondensedMedium" size:28];
[self doHeartBeat];
self.pulseTimer = [NSTimer scheduledTimerWithTimeInterval:(60. / self.heartRate) target:self selector:@selector(doHeartBeat) userInfo:nil repeats:NO];
}
return;
}
这是Swift代码:
func peripheral(peripheral: CBPeripheral!,
didUpdateValueForCharacteristic characteristic: CBCharacteristic!,
error: NSError!) -> String
{
// Get the Heart Rate Monitor BPM
var data = characteristic.value
var reportData = data.bytes
var bpm : UInt16
var rawByte : UInt8
var outputString = ""
rawByte = UInt8(reportData[0])
bpm = 0
if ((rawByte & 0x01) == 0) { // 2
// Retrieve the BPM value for the Heart Rate Monitor
bpm = UInt16( reportData[4] )
}
else {
bpm = CFSwapInt16LittleToHost(UInt16(reportData[1]))
}
outputString = String(bpm)
return outputString
}
const uint8_t *reportData = [data bytes];
翻译成
let reportData = UnsafePointer<UInt8>(data.bytes)
然后reportData
的类型为UnsafePointer<UInt8>
,您可以像在(Objective-)C中一样访问它:
if (reportData[0] & 0x01) == 0 { ... }
下一个,
bpm = reportData[1];
在Swift中几乎完全相同。 您必须显式地从UInt8
转换为UInt16
因为 - 与(Objective-)C不同 - Swift不会在类型之间隐式转换:
bpm = UInt16(reportData[1])
把它放在一起:
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)
}
// ...
}
请注意,大多数变量都可以使用let
而不是var
声明为常量 。 代替
bpm = CFSwapInt16LittleToHost(bpm)
您也可以使用littleEndian:
构造函数,它可用于所有整数类型:
bpm = UInt16(littleEndian: bpm)
Swift 3/4更新:
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 } )
}
// ...
}
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