Xamarin iOS低功耗蓝牙-CBPeripheral.UpdatedCharacteristicValue读取TX特性显示意外数据

Question

I recently received a BLE device for Bluetooth to Serial. It uses TruConnect and I'm trying to get it to communicate with my serial device. The serial device receives communication over a serial cable and echoes back anything that is sent to it as well as any results from a command that is sent.

Right now I'm simply trying to send TruConnect commands to the BLE device to check the current baud rate that the BLE device is set for.

I wrote some code based on this TruConnect guide that I found: https://truconnect.ack.me/1.5/apps/communicating_via_ble#reading_from_a_truconnect_device_serial_interface .

The problem seems to be that whenever I try to read anything from the tx characteristic when there should be data, the data is not right.

Setting up CBPeripheral events:

private void setupPerif(CBPeripheral perf)
{
    selectedPeripheral = perf;

    selectedPeripheral.UpdatedCharacterteristicValue += (sender, e) =>
    {
        var c = e.Characteristic;
        if (c != null)
        {
            var uuid = c.UUID.ToString(true).ToLower();
            if (uuid == UUID_RX)
            {
                //
            }
            else if (uuid == UUID_TX)
            {
                // expecting bytes to contain valid response data
                // it almost always contains twenty 0s.
                byte[] bytes = c.Value.Where(i => i != 13).ToArray();
                var invalidBytes = c.Value.Where(i => i > 127).ToArray();
                var nonZeros = c.Value.Where(i => i != 0).ToArray();
                if (nonZeros.Length < 1)
                {
                    return;
                }
                else
                {
                    foreach (byte b in bytes)
                        handler.handleByteReceived((char)b);
                }
            }
            else if (uuid == UUID_MODE)
            {
                //
            }
        }
    };

    selectedPeripheral.DiscoveredService += (sender, e) =>
    {
        var services = selectedPeripheral.Services;
        if (services != null)
        {
            foreach (CBService service in services)
            {
                if (service.UUID.ToString(true).ToLower() == UUID_TRUCONNECT)
                {
                    truConnect = service;
                    selectedPeripheral.DiscoverCharacteristics(truConnect);
                }
            }
        }
    };

    selectedPeripheral.DiscoveredCharacteristic += (sender, e) =>
    {
        if (truConnect != null && truConnect.Characteristics != null)
        {
            foreach (CBCharacteristic c in truConnect.Characteristics)
            {
                var uuidString = c.UUID.ToString(true).ToLower();
                if (uuidString == UUID_RX)
                {
                    rx = c;

                }
                else if (uuidString == UUID_TX)
                {
                    tx = c;
                }
                else if (uuidString == UUID_MODE)
                {
                    mode = c;
                    // set to stream mode
                    selectedPeripheral.WriteValue(NSData.FromArray(new byte[] { MODE_COMMAND }), mode, CBCharacteristicWriteType.WithResponse);
                }
            }
        }
    };
    selectedPeripheral.WroteCharacteristicValue += (sender, e) =>
    {
        // if UUID is for RX, we just wrote to RX. Drill down to
        // TX characteristic and read it. This will trigger
        // the UpdatedCharacteristicValue event.
        string uuid = e.Characteristic.UUID.ToString(true).ToLower();
        if (uuid == UUID_RX)
        {
            var services = selectedPeripheral.Services;
            if (services != null)
            {
                foreach (CBService s in services)
                {
                    if (s.UUID.ToString(true).ToLower() == UUID_TRUCONNECT)
                    {
                        var charachteristics = s.Characteristics;
                        if (charachteristics != null && charachteristics.Length > 0)
                        {
                            foreach (CBCharacteristic c in charachteristics)
                            {
                                if (c.UUID.ToString(true).ToLower() == UUID_TX)
                                {
                                    Timer t = new Timer(new TimerCallback(delegate(object o)
                                    {
                                        selectedPeripheral.ReadValue(c);
                                    }), null, TimeSpan.FromMilliseconds(100), TimeSpan.FromMilliseconds(-1));
                                }
                            }
                        }
                    }
                }
            }
        }
    };
    manager.ConnectPeripheral(selectedPeripheral);
}

Writes to rx. This is what should be used to actually send commands.

public void sendCommand(string command)
{
    command += endString + "\n";
    if (rx != null)
    {
        NSData d = NSData.FromString(command);

        foreach (CBService s in selectedPeripheral.Services)
        {
            if (s.UUID.ToString(true).ToLower() == UUID_TRUCONNECT)
                foreach (CBCharacteristic c in s.Characteristics)
                {
                    if (c.UUID.ToString(true).ToLower() == UUID_RX)
                        selectedPeripheral.WriteValue(NSData.FromString(command), c, CBCharacteristicWriteType.WithResponse);
                }
        }
    }
}

So my question is, why am I not getting the expected data when the CBPeripheral.UpdatedCharacteristicValue event is called? Occasionally I will get the expected data, but it is quite rare, and I can't seem to find any logical reason or pattern that would explain why this is happening.

Answer 1

AHA! I figured it out!

The problem was that I need to set the notify value for the appropriate characteristics. After doing that, I didn't need to call CBPeripheral.ReadValue(CBCharacteristic) .

    selectedPeripheral.DiscoveredCharacteristic += (sender, e) =>
    {
        if (truConnect != null && truConnect.Characteristics != null)
        {
            foreach (CBCharacteristic c in truConnect.Characteristics)
            {
                var uuidString = c.UUID.ToString(true).ToLower();
                if (uuidString == UUID_RX)
                {
                    rx = c;
                }
                else if (uuidString == UUID_TX)
                {
                    tx = c;
                    // set the notify value to true and poof!
                    // now CBPeripheral.UpdatedCharacteristicValue
                    // event will be triggered at the appropriate time.
                    selectedPeripheral.SetNotifyValue(true, tx);
                }
                else if (uuidString == UUID_MODE)
                {
                    mode = c;
                    // set to remote command mode
                    selectedPeripheral.WriteValue(NSData.FromArray(new byte[] { MODE_COMMAND }), mode, CBCharacteristicWriteType.WithResponse);
                }
            }
        }
    };