user exit on ME21N

hi all,

i have to check something BEFORE click on Save button on this tx, so.. i'm looking for the u.exit/exit/badi/etc inside this tx by the program zuserexit..

This program show me a list of exits.. various of them are'nt created yet and some others have no code inside..

Question: to see which user exit i can use, there are another way to enter one by one and clicking on the break-point button?

I need something (userexit/exit/bapi/badi) that works when i click on SAVE button on me21n, but BEFORE all data will be saved..

sorry for my BAD english..

Regards and have a good week!