4. Messages - Messages and system input and output

Several functions are provided in order to receive and submit system messages, i.e. messages to be displayed in an output area or in a status or progress bar. In order to display those messages in a proper place in the application, the application may set an application context (typically the ProjectContext ) by calling Application ::context() . In order to redirect messages submitted by SystemClass functions to the proper output area of the application, the context assigned as system context should overload the subsequent functions:

• input - receive data from user input ( input() )
• output - write message to standard output area ( SystemClass ::Message() , output() )
• startProgress - initialize progress display ( startProgress() )
• displayProgress - display progress state ( displayProgress() )
• stopProgress - deinitialize progress display stopProgress() )
• statusMessage - show message on status line ( statusMessage() )

Those functions allow submitting messages by calling the appropriate SystemClass functions