Graphics Programming Considerations Graphics Programming Considerations Buttons and menus can be monitored in the same window. However, the code will get complicated, and you might consider using different windows when the button and menu structure becomes complex. Only one pull-down menu can be active at any time. Design your windows with the following mechanical and aesthetic considerations: l Keep your windows as simple and uncluttered as possible. Use color carefully and purposefully. l If you are using multiple windows, use similar graphic elements so the screen elements become familiar and intuitive. l Let the operator know what is going on.
Never leave the operator in the dark as to the status of a button push or menu selection. l Whenever possible, have your windows mimic the real work world of the operator. In the interest of clarity, the examples in this chapter have not been generalized. When you actually program an application, use generalized subroutine calls for commonly used code, or your code will quickly become unmanageable. Using IOSTAT( ) The example code in this chapter leaves out critical error detection and recovery procedures. Effective application code requires these procedures. The IOSTAT function should be used to build error-handling routines for use with every ATTACH, FOPEN, FCLOSE, and FSET instruction.
The syntax for using IOSTAT to check the status of I/O requests is: IOSTAT(lun) lun The LUN specified in the previous I/O request. The IOSTAT function returns the following values: 1 if the last operation was successful 0 if the last operation is not yet complete if the last operation failed, a negative number corresponding to a standard Omron Adept error code will be returned. The following code checks for I/O errors: ; Issue I/O instruction (ATTACH, FOPEN, etc.) ;your code to handle the error END ; The ERROR function can be used to return the text IF IOSTAT(lun) 0 THEN eV+Language User's Guide, v2.x, 18318-000 Rev A Page 174