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Definition of ALV.
ALV(ABAP List Viewer) is a flexible tool for displaying lists. The tool provides common list operations as generic functions and can be enhanced by self-defined options.

ALV types and Corresponding Function modules.

1. ALV List or ALV Grid Display.
2. Hierarchical Sequential ALV Display.
3. Blocked ALV.
4. Blocked Hierarchical Sequential ALV Display.

In General, Otherthan OOPs concepts, ALV is just calling right Function module in the SE38 report and passing right parameters to the function module.
Function modules used for different kind of ALVs.

TYPE-POOLS:SLIS.
We define global internal tables, structures and Variables in the dictionary using TYPE GROUPS. To use those in the program we use TYPE-POOLS statement. All parameters which pass through Function module should refer SLIS variables, Structures, Internal tables.
Fieldcatalog.
It contains field descriptions which are displayed on output using ALV. We build fieldcatalog internal table.
Events in ALV
If we use ALV function modules to produce Output, Classical events are not triggered.For example TOP-OF-PAGE , END-OF-PAGE and secondary list events AT LINE-SELECTION, AT USER-COMMANDs.
If you want to know what are the events available for different kind of ALV specified above, Execute REUSE_ALV_EVENTS_GET function module and list type.Possible list types:0,1,2,3,4.

• 0 = simple list REUSE_ALV_LIST_DISPLAY
• 1 = hierarchcal-sequential list REUSE_ALV_HIERSEQ_LIST_DISPLAY
• 2 = simple block list REUSE_ALV_BLOCK_LIST_APPEND
• 3 = hierarchical-sequential block list REUSE_ALV_BLOCK_LIST_HS_APPEND
• 4 = Fullscreen REUSE_ALV_GRID_DISPLAY

For Any kind of ALV report, minimum required events are

1. TOP_OF_PAGE.
2. USER_COMMAND.
3. PF_STATUS_SET.
4. END_OF_LIST.