Functional

*) void KIWAY::ExpressMail( FRAME_T aDestination, MAIL_T aCommand, const std::string& aPayload, wxWindow* aSource=NULL );
*) virtual void KiwayMailIn( KIWAY_EXPRESS& aEvent );
*) enum MAIL_T expansion into the brave new world if cross KIWAY_PLAYER communications.

Let the KIWAY_PLAYING begin.....
through well conceived mail from one KIWAY_PLAYER to another.
Get thinking now.  Add a new MAIL_T value, then send ExpressMail(), 
and receive it in KiwayMailIn(), it's that easy.

common/kiway.cpp

@@ -37,6 +37,7 @@ KIFACE* KIWAY::m_kiface[KIWAY_FACE_COUNT];
 int     KIWAY::m_kiface_version[KIWAY_FACE_COUNT];
 
 
+
 KIWAY::KIWAY( PGM_BASE* aProgram, wxFrame* aTop ):
     m_program( aProgram ),
     m_top( 0 )
@@ -317,8 +318,7 @@ bool KIWAY::ProcessEvent( wxEvent& aEvent )
 
         if( alive )
         {
-#if 0
-            // This is still broken, but is the way to go.
+#if 1
             return alive->ProcessEvent( aEvent );
 #else
             alive->KiwayMailIn( *mail );

common/kiway_express.cpp

@@ -27,7 +27,18 @@
 //IMPLEMENT_DYNAMIC_CLASS( KIWAY_EXPRESS, wxEvent )
 
 
+#if 0   // requires that this code reside in only a single link image, rather than
+        // in each of kicad.exe, _pcbnew.kiface, and _eeschema.kiface as now.
+        // In the current case wxEVENT_ID will get a different value in each link
+        // image.  We need to put this into a shared library for common utilization,
+        // I think that library should be libki.so.  I am reluctant to do that now
+        // because the cost will be finding libki.so at runtime, and we need infrastructure
+        // to set our LIB_ENV_VAR to the proper place so libki.so can be reliably found.
+        // All things in due course.
 const wxEventType KIWAY_EXPRESS::wxEVENT_ID = wxNewEventType();
+#else
+const wxEventType KIWAY_EXPRESS::wxEVENT_ID = 30000;    // commmon accross all link images, hopefully unique.
+#endif
 
 
 KIWAY_EXPRESS::KIWAY_EXPRESS( const KIWAY_EXPRESS& anOther ) :

common/kiway_player.cpp

@@ -8,7 +8,9 @@
 BEGIN_EVENT_TABLE( KIWAY_PLAYER, EDA_BASE_FRAME )
     /* have not been able to get this to work yet:
     EVT_KIWAY_EXPRESS( KIWAY_PLAYER::kiway_express )
-    Use Connect() in constructor until this can be sorted out
+    Use Connect() in constructor until this can be sorted out.
+
+    OK the problem is KIWAY_PLAYER::wxEVENT_ID not being unique accross all link images.
     */
 END_EVENT_TABLE()
 

eeschema/cross-probing.cpp

@@ -30,6 +30,7 @@
 #include <fctsys.h>
 #include <pgm_base.h>
 #include <kiface_i.h>
+#include <kiway_express.h>
 #include <macros.h>
 #include <eda_dde.h>
 #include <wxEeschemaStruct.h>
@@ -176,19 +177,27 @@ void SCH_EDIT_FRAME::SendMessageToPCBNEW( EDA_ITEM* aComponent, SCH_COMPONENT* a
             SendCommand( MSG_TO_PCB, packet.c_str() );
         else
         {
-            Kiway().ExpressMail( FRAME_PCB, 0, packet, this );
+            // Typically ExpressMail is going to be s-expression packets, but since
+            // we have existing interpreter of the cross probe packet on the other
+            // side in place, we use that here.
+            Kiway().ExpressMail( FRAME_PCB, MAIL_CROSS_PROBE, packet, this );
         }
     }
 }
 
 
-#include <kiway_express.h>
-
 void SCH_EDIT_FRAME::KiwayMailIn( KIWAY_EXPRESS& mail )
 {
-    // @todo switch on command type
-    std::string payload = mail.GetPayload();
+    const std::string& payload = mail.GetPayload();
 
+    switch( mail.Command() )
+    {
+    case MAIL_CROSS_PROBE:
         ExecuteRemoteCommand( payload.c_str() );
+        break;
+
+    // many many others.
+
+    }
 }
 

include/kiway_express.h

@@ -29,6 +29,20 @@
 #include <wx/wx.h>
 #include <frame_type.h>
 
+
+/**
+ * Enum MAIL_T
+ * is the set of mail types sendable via KIWAY::ExpressMail() and supplied as
+ * the @a aCommand parameter to that function.  Such mail will be received in
+ * KIWAY_PLAYER::KiwayMailIn( KIWAY_EXPRESS& aEvent ) and aEvent.Command() will
+ * match aCommand to ExpressMail().
+ */
+enum MAIL_T
+{
+    MAIL_CROSS_PROBE,
+};
+
+
 /**
  * Class KIWAY_EXPRESS
  * carries a payload from one KIWAY_PLAYER to anothing within a PROJECT.
@@ -42,6 +56,15 @@ public:
      */
     FRAME_T  Dest()                         { return m_destination; }
 
+    /**
+     * Function Command
+     * returns the EXPRESS_MAIL_T associated with this mail.
+     */
+    MAIL_T Command()
+    {
+        return (MAIL_T) GetId();    // re-purposed control id.
+    }
+
     /**
      * Function Payload
      * returns the payload, which can be any text but it typicall self

pcbnew/cross-probing.cpp

@@ -13,6 +13,7 @@
 #include <fctsys.h>
 #include <pgm_base.h>
 #include <kiface_i.h>
+#include <kiway_express.h>
 #include <wxPcbStruct.h>
 #include <eda_dde.h>
 #include <macros.h>
@@ -206,19 +207,27 @@ void PCB_EDIT_FRAME::SendMessageToEESCHEMA( BOARD_ITEM* aSyncItem )
             SendCommand( MSG_TO_SCH, packet.c_str() );
         else
         {
-            Kiway().ExpressMail( FRAME_SCH, 0, packet, this );
+            // Typically ExpressMail is going to be s-expression packets, but since
+            // we have existing interpreter of the cross probe packet on the other
+            // side in place, we use that here.
+            Kiway().ExpressMail( FRAME_SCH, MAIL_CROSS_PROBE, packet, this );
         }
     }
 }
 
 
-#include <kiway_express.h>
-
 void PCB_EDIT_FRAME::KiwayMailIn( KIWAY_EXPRESS& mail )
 {
-    // @todo switch on command type
-    std::string payload = mail.GetPayload();
+    const std::string& payload = mail.GetPayload();
 
+    switch( mail.Command() )
+    {
+    case MAIL_CROSS_PROBE:
         ExecuteRemoteCommand( payload.c_str() );
+        break;
+
+    // many many others.
+
+    }
 }