NSLocalizedDescription =不允许写

Question

我尝试制作一个将消息从iPhone发送到Bluetooth LE模块的应用程序。但是由于某种原因，它会出现以下错误：

  

NSLocalizedDescription =不允许写。

即使 blePeripheral 和 blePeripheral！.write 的类型为CBCharacteristicWrite.withResponse ，错误表明不允许写作。为什么下面的代码对我不起作用？

func writeValue(data: String) {
    let valueString = (data as NSString).data(using: String.Encoding.utf8.rawValue)
    //change the "data" to valueString
    if let blePeripheral = blePeripheral {
        if let txCharacteristic = txCharacteristic {
            blePeripheral.writeValue(valueString!, for: txCharacteristic, type: CBCharacteristicWriteType.withResponse)
        }
    }
}

func writeCharacteristic(val: Int8) {
    var val = val
    let ns = NSData(bytes: &val, length: MemoryLayout<Int8>.size)
    blePeripheral!.writeValue(ns as Data, for: txCharacteristic!, type: CBCharacteristicWriteType.withResponse)
}

我在其中找到代码的资源是： https://learn.adafruit.com/crack-the-code/communication