title: Change Data of itab bound to CL_GUI_ALV_GRID programmatically and fire event DataChanged
body: <p>I'm currently facing the following problem:
  In my abap program I am using an ALV grid to display a list of data.
  Now I have got the requirement to convert the data of cell 5 depending on the value entered in cell 3. Normally I could just do this by implementing a handler method for the DataChanged or DataChangedFinished events.</p>
  
  <p>But in my case the value of cell 3 is written into the backend table i connected to the alv grid when creating it via the method SET_TABLE_FOR_FIRST_DISPLAY. That means the alv does not register it when the data is changed. I also tried to use the method CHANGE_DATA_FROM_INSIDE of CL_GUI_ALV_GRID and this partly works if I set the value of VAL_DATA in the layout structure to 'X' when initializing the grid. The program runs through my handler for the DataChanged event.
  But in my case it results in a short dump because the method can only work with caracter fields and I need cell 3 and cell 5 to be decimals. The dump is caused in the GET_CHANGED_DATA method of CL_GUI_ALV_GRID. When I am applying this mechanism to character fields it works fine.</p>
  
  <p>This question refers to the following thread where I got the idea of setting the VAL_DATA flag of the layout structure from:
  <a href="https://stackoverflow.com/questions/17165710/how-to-trigger-the-data-change-event-of-cl-gui-alv-grid-or-why-isnt-it-trigger">StackOverFlow Question</a></p>
  
  <p>Did anyone ever face the same problem? Do you have any advice for me?</p>