IPF and its communication objects communicate through window and help manager messages. IPF communication objects, and windows that they create, can send messages to IPF and IPF windows for which the communication objects can get a handle. Similarly, IPF can send messages to any window that a communication object creates.

Any message that an application can send to IPF also can be sent by IPF communication objects. As a programmer working with communication objects, you will need to understand the following important help manager messages:

• HM_CONTROL
  
• HM_INFORM
  
• HM_INVALIDATE_DDF_DATA
  
• HM_NOTIFY
  
• HM_QUERY
  
• HM_QUERY_DDF_DATA
  
• HM_SET_COVERPAGE_SIZE
  
• HM_SET_OBJCOM_WINDOW
  
• HM_SET_USERDATA
  
• HM_UPDATE_OBJCOM_WINDOW_CHAIN

For a detailed description of these messages and other IPF messages, see Help Manager Messages.