ReadHandler

The ReadHandler interface is the mechanism by which measurement data received from the outstation is passed to user code. This callback interface is specified for each association created. It is invoked for unsolicited and responses to polls.

When a response or unsolicited response is parsed and determined to carry measurement data, callbacks are made in the following order:

1. ReadHandler::beginFragment
2. ReadHandler::handle<TYPE> for each object header in the message.
3. ReadHandler::endFragment

The begin/end methods provide useful information:

• The full header of the response
• Context regarding what triggered the response, e.g. unsolicited, startup integrity scan, periodic poll, etc

tip

It is common to maintain a list of measurement values in your ReadHandler implementation and then use the endFragment method as a trigger for publishing them. Since responses may consist of multiple fragments, you may also want to check that ResponseHeader.Control.Fin is set to true indicating that the current fragment is the final fragment in the response series.