ABAP Dialog 为什么用自定义OK_code 而不用系统变量sy-ucomm

In each PAI event that a user triggers by choosing either a pushbutton on the screen or an element in a GUI status, the corresponding function code is placed into the system field syst-ucomm or sy-ucomm and placed in the OK_CODE field (as long as the function code is not empty). Empty function codes are placed in neither the sy-ucomm field nor the OK_CODE field. In each PAI event that a u