Creating custom NMEA messages

Custom NMEA messages can be registered for parsing as well. To create a new message, add the NmeaMessageType attribute to the class, and declare the 5-character message type.

Note: You can use -- as the first two characters to make it independent of the Talker Type.

Next ensure you have a constructor that takes the TypeName string parameter first, and a second string[] parameter that will contain all the message values:

Example:

[NmeaMessageType("PTEST")]
public class CustomMessage : NmeaMessage
{
    public CustomMessage(string type, string[] parameters) : base(type, parameters)
    {
        Value = parameters[0];
    }
    public string Value { get; }
}

Next register this with the NMEA Parser using either:

NmeaMessage.RegisterAssembly(typeof(CustomMessage).Assembly); //Registers all types in the provided assembly
NmeaMessage.RegisterMessage(typeof(CustomMessage).GetTypeInfo());  //Registers a single NMEA message

Note that these methods will throw if the NMEA type has already been registered (there's an overload where you can declare the replace parameter to true to overwrite already registered messages.

Next you should be able to test this method using the Parse method:

var input = "$PTEST,TEST*7C";
var msg = NmeaMessage.Parse(input);

Creating a multi-sentence message

A NMEA message cannot exceed 82 characters, so often messages are split into multiple sentences. To create a custom multi message, either implement IMultiSentenceMessage or simply subclass NmeaMultiSentenceMessage.

[NmeaMessageType("PTST2")]
private class CustomMultiMessage : NmeaMultiSentenceMessage, IMultiSentenceMessage
{   
    public CustomMultiMessage(string type, string[] parameters) : base(type, parameters)
    {
    }
    public string Id { get; private set; }
    public List<string> Values { get; } = new List<string>();
    // Set index in the message where the total count is:
    protected override int MessageCountIndex => 0;
    // Set index in the message where the message number is:
    protected override int MessageNumberIndex => 1;
    protected override bool ParseSentences(Talker talkerType, string[] message)
    {
        // Ensure this message matches the previous message.
        // Use any indicator to detect message difference, so you can error out and avoid
        // appending the wrong message
        if (Id == null)
            Id = message[2]; //First time it's not set
        else if (Id != message[2])
            return false;
        Values.AddRange(message.Skip(3));
        return true;
    }
}

Note that the message is parsed in the ParseSentences method, and not the constructor. Also note that the talkerType is parsed to you, because multi-sentence messages allows a mix of talker types, if you use the -- prefex in the NMEA type.

Next we can parse the two messages and have the second one be appended to the first one:

NmeaMessage.RegisterNmeaMessage(typeof(CustomMultiMessage).GetTypeInfo());
var input1 = "$PTST2,2,1,123,A,B,C,D*2A";
var input2 = "$PTST2,2,2,123,E,F,G,H*21";
var msg1 = NmeaMessage.Parse(input1);
var msg2 = NmeaMessage.Parse(input2, msg1 as IMultiSentenceMessage);

If msg1 and msg2 aren't the same instance, it means the message couldn't be added to the previous message, and a new message was generated.