Basic ALV (ABAP List Viewer) beginners tutorial

Here’s how a simple ALV list can be programmed. This is one of the most basic tasks you get assigned to as a developer.

Step I – Declaring variables

REPORT ZALVTEST.

TABLES: t001w.

DATA: gt_plants TYPE TABLE OF t001w.  
DATA: gr_alv    TYPE REF TO   cl_salv_table.

The ‚TABLES‚ keyword declares a structure (type: T001W = table of plants) which is refered to when we define our SELECT-OPTIONS.
gt_plants is an internal table (a.k.a. ‚array‘) which holds the data to be displayed in an ALV
gr_alv is a so called object reference to the ALV class (Transaction SE24 => ‚cl_salv_table‘)

Step II – Creating a selection screen
In order for the user to be able to select certain plants, we give him select options.

SELECT-OPTIONS: so_werks FOR t001w-werks,
                so_land1 FOR t001w-land1.

See how the previously declared structure T001W is referenced here (FOR t001w-werks).

Step III – Reading data with Open SQL

START-OF-SELECTION.

SELECT * FROM t001w
  INTO TABLE gt_plants
  WHERE werks IN so_werks
    AND land1 IN so_land1.

The keyword ‚START-OF-SELECTION‚ declares a so called event. Basically it defines the code block where most of the action happens.
See how the select options are used in the WHERE clause of the SQL statement.
Hint: If the select options are left empty on the selection screen, all data are being selected.

Step IV – Creating and displaying the ALV table

END-OF-SELECTION.

IF NOT gt_plants[] IS INITIAL.
* Build alv reference
  CALL METHOD cl_salv_table=>factory
    IMPORTING
      r_salv_table = gr_alv
    CHANGING
      t_table      = gt_plants. 

* Finally, show alv
  CALL METHOD gr_alv->display( ).
ELSE.
  MESSAGE i208(00) WITH 'No plants found!'.
ENDIF.

The keyword ‚END-OF-SELECTION‚ basically says: All main operations complete, start the final actions.
The first thing we do inside the END-OF-SELECTION code block is to check if the internal table which should be displayed holds any data. If not, we display a basic information.

Now to a little ABAP objects:
In order to display the ALV, we have to do 2 things at least:
a) Create the ALV object
b) Tell the ALV object to display itself.

a) Is done via a static method call of the class CL_SALV_TABLE and method FACTORY.
The internal table GT_PLANTS is handed over to the method and the object reference GR_ALV is given back to us (us = the calling program).
Note:
– You can identify static method calls via the ‚=>‘
– Static method means: You don’t have to create an instance of the class prior to calling the method.

b) This is done via a so called instance method call of the object GR_ALV and method DISPLAY.
Note:
– You can identify instance method calls via the ‚->‘
– Calling instance methods is only possible if you have an object reference which, in this case, we got from a) 🙂

Here is what the complete report looks like in an actual SAP system:
zalvtest

And this is what our very basic ALV looks like:
Very basic ALV

Addendum:
In order to make the select-options more beautiful, i.e. readable, you can do the following:
seltexts

seltexts2

seltexts3

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