Example: Single Data Type Data

The following procedures build a simple application that allows the user to select data from a table, plotting the data in a draw window and optionally displaying the data values in a text widget. The user can switch the table between standard and disjoint selection modes.

Example Code
This example is included in the file table_widget_example1.pro in the examples/doc/widgets subdirectory of the IDL distribution. Run this example procedure by entering table_widget_example1 at the IDL command prompt or view the file in an IDL Editor window by entering .EDIT table_widget_example1.pro. See Running the Example Code if IDL does not run the program as expected.

; Event-handler routine 
PRO table_widget_example1_event, ev 
 
  ; Retrieve the anonymous structure contained in the user value of 
  ; the top-level base widget. 
  WIDGET_CONTROL, ev.top, GET_UVALUE=stash 
 
  ; Retrieve the table's selection mode and selection. 
  disjoint = WIDGET_INFO(stash.table, /TABLE_DISJOINT_SELECTION) 
  selection = WIDGET_INFO(stash.table, /TABLE_SELECT) 
 
  ; Check to see whether a selection exists, setting the 
  ; variable 'hasSelection' accordingly. 
  IF (selection[0] ne -1) THEN hasSelection = 1 $ 
    ELSE hasSelection = 0 
 
  ; If there is a selection, get the value. 
  IF (hasSelection) THEN WIDGET_CONTROL, stash.table, $ 
    GET_VALUE=value, /USE_TABLE_SELECT 
 
  ; The following sections define the application's reactions to 
  ; various types of events. 
 
  ; If the event came from the table, plot the selected data. 
  IF ((ev.ID eq stash.table) AND hasSelection) THEN BEGIN 
    WSET, stash.draw 
    PLOT, value 
  ENDIF 
 
  ; If the event came from the 'Show Selected Data' button, display 
  ; the data in the text widget. 
  IF ((ev.ID eq stash.b_value) AND hasSelection) THEN BEGIN 
    IF (disjoint eq 0) THEN BEGIN 
      WIDGET_CONTROL, stash.text, SET_VALUE=STRING(value, /PRINT) 
    ENDIF ELSE BEGIN 
      WIDGET_CONTROL, stash.text, SET_VALUE=STRING(value) 
    ENDELSE 
  ENDIF 
 
  ; If the event came from the 'Show Selected Cells' button, 
  ; display the selection information in the text widget. Use 
  ; different displays for standard and disjoint selections. 
  IF ((ev.ID eq stash.b_select) AND hasSelection) THEN BEGIN 
    IF (disjoint eq 0) THEN BEGIN 
      ; Create a string array containing the column and row 
      ; values of the selected rectangle. 
      list0 = 'Standard Selection' 
      list1 = 'Left:   ' + STRING(selection[0]) 
      list2 = 'Top:    ' + STRING(selection[1]) 
      list3 = 'Right:  ' + STRING(selection[2]) 
      list4 = 'Bottom: ' + STRING(selection[3]) 
      list = [list0, list1, list2, list3, list4] 
    ENDIF ELSE BEGIN 
      ; Create a string array containing the column and row 
      ; information for the selected cells. 
      n = N_ELEMENTS(selection) 
      list = STRARR(n/2+1) 
      list[0] = 'Disjoint Selection' 
      FOR j=0,n-1,2 DO BEGIN 
        list[j/2+1] = 'Column: ' + STRING(selection[j]) + $ 
          ', Row: ' + STRING(selection[j+1]) 
      ENDFOR 
    ENDELSE 
    WIDGET_CONTROL, stash.text, SET_VALUE=list 
  ENDIF 
 
  ; If the event came from the 'Change Selection Mode' button, 
  ; change the table selection mode and the title of the button. 
  IF (ev.ID eq stash.b_change) THEN BEGIN 
    IF (disjoint eq 0) THEN BEGIN 
      WIDGET_CONTROL, stash.table, TABLE_DISJOINT_SELECTION=1 
      WIDGET_CONTROL, stash.b_change, $ 
        SET_VALUE='Change to Standard Selection Mode' 
    ENDIF ELSE BEGIN 
      WIDGET_CONTROL, stash.table, TABLE_DISJOINT_SELECTION=0 
      WIDGET_CONTROL, stash.b_change, $ 
        SET_VALUE='Change to Disjoint Selection Mode' 
    ENDELSE 
  ENDIF 
 
  ; If the event came from the 'Quit' button, close the 
  ; application. 
  IF (ev.ID eq stash.b_quit) THEN WIDGET_CONTROL, ev.TOP, /DESTROY 
 
END 
 
; Widget creation routine. 
PRO table_widget_example1 
 
  ; Create data to be displayed in the table. 
  data = DIST(7) 
 
  ; Create initial text to be displayed in the text widget. 
  help = ['Select data from the table below using the mouse.'] 
 
  ; Create the widget hierarchy. 
  base = WIDGET_BASE(/COLUMN) 
  subbase1 = WIDGET_BASE(base, /ROW) 
  draw = WIDGET_DRAW(subbase1, XSIZE=250, YSIZE=250) 
  subbase2 = WIDGET_BASE(subbase1, /COLUMN) 
  text = WIDGET_text(subbase2, XS=50, YS=8, VALUE=help, /SCROLL) 
  b_value = WIDGET_BUTTON(subbase2, VALUE='Show Selected Data') 
  b_select = WIDGET_BUTTON(subbase2, VALUE='Show Selected Cells') 
  b_change = WIDGET_BUTTON(subbase2, $ 
    VALUE='Change to Disjoint Selection Mode') 
  b_quit = WIDGET_BUTTON(subbase2, VALUE='Quit') 
  table = WIDGET_TABLE(base, VALUE=data, /ALL_EVENTS) 
 
  ; Realize the widgets. 
  WIDGET_CONTROL, base, /REALIZE 
 
  ; Get the widget ID of the draw widget. 
  WIDGET_CONTROL, draw, GET_VALUE=drawID 
 
  ; Create an anonymous structure to hold widget IDs. This 
  ; structure becomes the user value of the top-level base 
  ; widget. 
  stash = {draw:drawID, table:table, text:text, b_value:b_value, $ 
           b_select:b_select, b_change:b_change, b_quit:b_quit} 
 
  ; Set the user value of the top-level base and call XMANAGER 
  ; to manage everything. 
  WIDGET_CONTROL, base, SET_UVALUE=stash 
  XMANAGER, 'table_widget_example1', base 
 
END

The following things about this example are worth noting:

It is important to check whether a selection exists before using WIDGET_CONTROL to retrieve the selection.

Data from disjoint selections is handled differently than data from standard selections.

For a relatively simple application, passing a group of widget IDs via the top-level base widget's user value allows the use of a single event routine rather than separate event routines for each widget.