RobotStudio event

How to record signals via RS SDK

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Hi ,         
          I want to design my add-ins to record the signals into text file.The RobotStudio has the APIs about how to do this ,but it doesn't give a thorough example.I don't understand how to do it.I have tried to use DataRecorderSignal  and create a singal sink,but I don't know how I get the value of the signal.Could  anyone help me ? Thanks for the help!