References: http://www.cnblogs.com/carysun/archive/2009/12/06/wf4-activitycorrelation.html
The above links have more comprehensive information, which is just a key point. I have spent a few hours experimenting with this experiment. I hope you can avoid detours.
1. Use send to send messages. (Note that you cannot call methods with returned values)
2. Send and receivereply for sending and receiving responses. (Must be used in conjunction with activities)
3. Send key attributes and parameters. (The parameter names must be consistent)
4. receivereply activity key attributes and parameters (The format of the returned parameter name is "method name + result ")
I do not have a very systematic knowledge of WF. The problem may be caused by insufficient understanding of WF. The document is only used as a work note.
Demo download: http://files.cnblogs.com/yizhuqing/WFCallWCF.rar