Refreshing the user interface

Genero BDL only refreshes the user interface when the runtime waits for user interaction. In certain scenarios, this can result in information displayed in an I4GL application not being displayed when running as a Genero BDL application.

To optimize the display, the Genero runtime system only refreshes the screen when the user gets the control back. In other words, when an interactive instruction (a dialog) waits for a user interaction.

Important: In most cases, the user interface refresh behavior of Genero BDL (where the output is delayed until the runtime waits for a user interaction) does not introduce any display problem in legacy programs. However, attention is required when information must be immediately visible while the runtime continues processing code. A typical example is a "Please wait..." message, displayed just before a lengthy processing.

IBM® Informix® 4GL behavior

IBM Informix 4GL (I4GL) only supports a TUI mode, displaying screens on dumb terminal or terminal emulators.

When a program executes an instruction displaying information to the user, IBM Informix 4GL refreshes the screen immediately.

For example, when doing successive DISPLAY ... AT instructions in a loop, I4GL will show screen changes for each DISPLAY instruction:
MAIN
    DEFINE i INTEGER
    MENU "Test"
        COMMAND "Start"
            FOR i=1 TO 50000
                DISPLAY i AT 5,5
            END FOR
        COMMAND "Quit"
            EXIT MENU
    END MENU
END MAIN

Genero BDL in TUI mode

The application runs in text (TUI) mode when FGLGUI=0. This section refers to an application running in TUI mode.

With the above code running in TUI mode, the screen will not show the numbers. It will only show the final number, when the MENU gives the control back to the user.

To display all of the numbers to the end user, force the screen refresh with an ui.Interface.refresh() API call.
MAIN
    DEFINE i INTEGER
    MENU "Test"
        COMMAND "Start"
            FOR i=1 TO 50000
                DISPLAY i AT 5,5
                CALL ui.Interface.refresh()
            END FOR
        COMMAND "Quit"
            EXIT MENU
    END MENU
END MAIN
Important: Forcing the user interface refresh as shown in this example must only be done when using the TUI mode. See GUI mode case for details.

Genero BDL in GUI mode

When using the GUI mode of Genero, instead of displaying directly to the terminal screen, the runtime system communicates with a front-end. See The dynamic user interface for more details.

With GUI mode, if the program refreshes the user interface too often, it will produce a lot of unnecessary network traffic. The user interface should be refreshed periodically rather than continuously, to avoid network clogging.

In the following code example, we have added the (i MOD 100)==0 test to reduce the number of refresh calls.

MAIN
    DEFINE i INTEGER
    MENU "Test"
        COMMAND "Start"
            FOR i=1 TO 5000000
                IF (i MOD 100) == 0 THEN
                    DISPLAY i AT 5,5
                    CALL ui.Interface.refresh()
                END IF
            END FOR
        COMMAND "Quit"
            EXIT MENU
    END MENU
END MAIN
Important: This code example is provide to explain the Genero behavior. Do not use this as a programming pattern! Let the runtime system refresh the user interface automatically when needed, and ONLY use ui.Interface.refresh() to update the display of messages like "Please wait..." before a lengthy processing.