Diff between at line selection and HIDE technique

Question

hi all,
       wht is the diff between at-line-selection and HIDE technique.
        wht r code instructor
        wht is extended testing
        how can we find selected error records in session                          method ex:-if there r errors in 4th 9th 13th record.
tthnx in advance

Answer 1

HIDE
Syntax
HIDE dobj.
Effect
This statement stores - in the current list level - the content of the variable dobj together with the current list line whose line number is contained in sy-linno. The data type of the variables dobj must be flat and no field symbols can be specified that point to rows of internal tables, and no class attributes can be specified. The stored values can be read as follows:
For each user action in a displayed screen list that leads to a list result, all the row values stored using HIDE - that is, the row on which the screen cursor is positioned at the time of the event - are assigned to the respective variables.
If a list row of an arbitrary list level is read or modified using the statements READ LINE or MODIFY LINE, all the values of this row stored using HIDE are assigned to the respective variables.
Notes
The HIDE statement works independently of whether the list cursor was set. In particular, variables for empty list rows can be stored - that is, rows in which the list cursor was positioned using statements like SKIP.
The HIDE statement should be executed immediately at the statement that has set the list cursor in the row.
Outside of classes, constants and literals that cannot be read in list results and in the statement READ LINE can be specified for dobj outside of classes.
Example
Storing square numbers and cubic numbers for a list of numbers. The example shows that arbitrary variables can be stored independently of row content. In the real situation, one would more likely store only the number and execute the calculation, when required, in the the event block for AT LINE-SELECTION.
REPORT ...
DATA: square TYPE i,
      cube   TYPE i.
START-OF-SELECTION.
  FORMAT HOTSPOT.
  DO 10 TIMES.
    square = sy-index ** 2.
    cube   = sy-index ** 3.
    WRITE / sy-index.
    HIDE: square, cube.
  ENDDO.
AT LINE-SELECTION.
  WRITE: square, cube.
AT LINE-SELECTION
Syntax
AT LINE-SELECTION.
Effect
This statement defines an event block whose event is triggered by the ABAP runtime environment during the display of a screen list - provided the scren cursor is on a list line and you select a function using the function code PICK. Through the definition of this event block, the standard list status is automatically enhanced in such a way that the function code F2 and, with it, the double-click mouse function is linked up to the function code PICK.
Note
If the function key F2 is linked with a function code different than PICK, each double click will trigger its even, usually AT USER-COMMAND, and not AT LINE-SELECTION.
Example
This program works with the standard list status. A line selection with the left mouse key causes the event AT LINE-SELECTION and creates details lists.
REPORT demo_at_line_selection.
START-OF-SELECTION.
  WRITE 'Click me!' COLOR = 5 HOTSPOT.
AT LINE-SELECTION.
  WRITE: / 'You clicked list', sy-listi,
         / 'You are on list',  sy-lsind.
  IF sy-lsind < 20.
    SKIP.
    WRITE: 'More ...' COLOR = 5 HOTSPOT.
  ENDIF.
Thanks,