如何使用writeValue与BLE外设通信以发送字符串？

Question

我正在尝试使用swift通过蓝牙连接将字符串发送到Nordic Semiconductor开发套件（nRF52840）。核心蓝牙提供了writeValue，在外围对象上调用它。我该如何使用呢？

我在网上看过，但是找不到如何发送数据的教程或指南。

func writeValue(data: String){
        //let valueString = (data as NSString).data(using: String.Encoding.utf8.rawValue)
        print("Checkpoint 1")
        let cafe = Data(data.utf8)
        //change the "data" to valueString
        if let blePeripheral = BLEControl.BLESingleton.connectedPeripheral{
            print("Checkpoint 2")
            if let txCharacteristic = txCharacteristic {
                print("Checkpoint 3")
                blePeripheral.writeValue(cafe, for: txCharacteristic, type: CBCharacteristicWriteType.withResponse)
            }
        }
    }


'''

The Code I am using is from Nordic Semiconductor's example basic communication found on this GitHub, https://github.com/nar0909/nRFSampleSwiftApp_iOS/tree/master/Basic-Chat-master/Basic%20Chat