Question

Good morning,

I am retrieving a stream of bytes from a serial device that connects to the iPad. Once connected the supplied SDK will call a delegate method with the bytes that have been forwarded.

The readings forwarded by the serial device via the SDK are in the following format:

!X1:000.0;

Once connected to the serial device the delegated methods will start receiving data immediately – this could be in various states of completion i.e.

:000.00;

What I need to do is establish a concrete way of splitting the readings returned from the serial device so that I can manipulate the data.

Some of the tried options are:

Simply concatenate the received strings for a fixed period and then split the NSString on the “;” character. This is a little inefficient though and does not allow me to manipulate the data dynamically

-(void)receivingDelegateMethod:(NSString *)aString    {
      if(counter < 60){
          [self.PropertyString stringByAppendingString:aString];
      }else{
          NSArray *readings = [self.PropertyString componentsSeparatedByString: @";"];
      }    
}

Determine a starting point by looking for the “!” character and then appending the resulting substring to a NSString property. All previous calls to the delegated method will append to this property and then remove the first 10 characters.

I know there are further options such as NSScanners and RegEx but I wanted to get the opinion of the community before wasting more time of different methods.

Thanks

Answer 1

Make a BOOL flag that indicates that the stream has been initialized, and set it to false. When you receive the next chunk of data, check the flag first. If it is not set, skip all characters until you see an exclamation point '!'. Once you see it, discard everything in front of it, and copy the rest of the string into the buffer. If the “is initialized” flag is set, append the entire string to the buffer without skipping characters.

Once you finish the append, scan the buffer for ! and ; delimited sections. For each occurrence of that pattern, call a designated method with a complete portion of the pattern. You can get fancy, and define your own “secondary” delegate for processing pre-validated strings.

You may need to detect disconnections, and set the “is initialized” flag back to NO.