How to add event to ofxSimpleGuiToo

I want ofxSimpleGuiToo to be able to notify my app when it is saving so it can save some other stuff. So I tried hacking an event into ofxSimpleGuiToo.h by adding a pointer to the function…

  
class ofxSimpleGuiToo {  
  
class i2App;  
  
typedef void(i2App::*notifySave)();  

However then I get the compiler warning:

…\dependencies\ofxmsaof\ofxSimpleGuiToo\src\ofxSimpleGuiToo.h|145|error: `ofxSimpleGuiToo’ does not name a type|

On this line:

  
extern ofxSimpleGuiToo gui;  

What strategy do I need to employ here ?

Best regards,

Chris.