Finishing the Widget Program

The final steps of the program involve closing the widgets and cleaning up the pointers. The event handler for the Done button closes the TLB widget, which closes all the other widgets. But the pointers you designated in the state structure still exist within IDL until you free them, which is done in the cleanup event handler.

Creating the Done Button Event Handler

This event handler is very simple, because it just destroys the top-level widget, which destroys all the other widgets within it. Place this event handling routine after the droplist procedure and above the primary procedure. (The primary procedure must always be the last procedure in the file.) 

; Event handler for the Done button. 
PRO basic_draw_doc_done, event 
 
  ; Destroy the top-level widget 
  ; (which destroys all other widgets). 
  WIDGET_CONTROL, event.top, /DESTROY 
END

In addition to this routine, you must also add some information to the WIDGET_BUTTON definition, telling it which event handler to use.

  1. Find the following lines in the basic_draw_doc procedure:
    2. button = WIDGET_BUTTON(base2, VALUE='Done', $ 
      UVALUE='done'
  2. At the end, add a comma and EVENT_PRO='basic_draw_doc_done' so that the lines now read:
    3. button = WIDGET_BUTTON(base2, VALUE='Done', $ 
      UVALUE='done', $ 
      EVENT_PRO='basic_draw_doc_done')
  3. Save the file, compile and run it.

You can now choose images from the droplist, resize, and close the widget. In the next section, we will add the final necessary event handler to clean up the pointers for the widget program.

Creating the Cleanup Procedure

The cleanup procedure frees the pointers on closing the widget. If you do not clean up the pointers, they are still available to IDL and may cause problems if you run another instance of the program.

Place this routine after the basic_draw_doc_done procedure and above the primary procedure, basic_draw_doc. (The primary procedure must always be the last procedure in the file.) 

; Cleanup procedure cleans up the pointers on closing the widget. 
PRO basic_draw_doc_cleanup, base 
 
  ; Clean up pointers. 
  WIDGET_CONTROL, base, GET_UVALUE=state 
  IF N_Elements(state) EQ 0 THEN RETURN 
  PTR_FREE, state.image 
END

In addition to this routine, you must also edit the XMANAGER statement, defining the cleanup procedure to use.

  1. Find the following lines at the end of the basic_draw_doc routine:
    2. XMANAGER, 'basic_draw_doc', base
  2. Add a comma and a line break ($) on the second line. Then add the third line as shown below:
    3. XMANAGER, 'basic_draw_doc', base, $ 
      Cleanup='basic_draw_doc_cleanup'
  3. Save the file, compile and run it.

Congratulations - you have just written an IDL widget program!

The program is now complete and should run as intended. You can choose any image from the droplist, resize the window and image, and cleanly close the program.

See IDL Pointers and Freeing Pointers for more information.

Note
If the program does not work correctly, check your code against the different routines shown in this tutorial. It's easy to miss adding the extra lines in the primary routine after you add the event handling routines. You can also compare your code to the full example program (draw_basic_doc.pro) in the examples\doc\widgets subfolder of your IDL distribution. Open the program by typing the following command on the IDL command line (or simply click on the link): .edit draw_basic_doc.pro