OpenEuphoria

1. NEWT :: selecting an item from a listbox

• Posted by K_D_R Dec 25, 2012
• 2088 views

I have been having a rough time trying to "capture" an item selected from a newt listbox form.

Consider example6.ex: The value assigned to listboxState appears to be an arbitrarily assigned pointer. But how can that value be used to reference the element in the sequence to which it refers?

The documentation states that "Each entry in a listbox is a ordered pair of the text which should be displayed for that item and a key, which is a void * thatuniquely identifies that listbox item. Many applications pass integers in as keys, but using arbitrary pointers makes many applications significantly easier to code." But how exactly does an application pass an integer in as a key? http://gnewt.sourceforge.net/tutorial-4.html#ss4.12

Any assistance will be deeply appreciated.

Kenneth Rhodes

3. Re: NEWT :: selecting an item from a listbox

• Posted by K_D_R Dec 26, 2012
• 1983 views

Thanks, Greg, for the sample code. I am still having problems - here is the code I have been working with, the comments will show variations I have tried.

 include ../newt.e 
include std/machine.e 
procedure main() 
 
-- create a simple list of things  
sequence fruits = { "Apples", "Bananas", "Oranges" }  
     
    newtComponent form,  
	listbox, 
	buttonSubmit 
     
    newt:Init() 
    newt:Cls() 
     
    newt:CenteredWindow( 64, 24, "*Select Item" ) 
  
 -- create a new list box  
    listbox = newt:Listbox( 2, 2, 5, NULL )  
--  listbox = newt:Listbox( 2, 2, 5, NEWT_FLAG_RETURNEXIT )  
--  listbox = newt:Listbox( 18, 3, 10, NEWT_FLAG_SCROLL )  
--  listbox = newt:Listbox( 18, 3, 10, NEWT_FLAG_SCROLL ) 
--  newt:ListboxAppendEntry(listbox, "", 0) 
--  newt:ListboxAppendEntries(listbox, fruits, 0) 
     
  -- loop through the items  
  for index = 1 to length( fruits ) do  
    
	    -- allocate some memory  
	   atom ptr = allocate( 4, 1 ) -- 1 = automatically free  
	     
	    -- store the index of this item  
	    poke4( ptr, index )  
		      
	    --  add the item to the list box  
     newt:ListboxAppendEntry( listbox, fruits[index], ptr )  
  end for  
			        
    buttonSubmit = newt:Button( 22, 20, "Submit" ) 
     
    form = newt:Form( NULL, NULL, 0 ) 
    newt:FormAddComponents( form, { 
	listbox, 
	buttonSubmit 
	}) 
     
    --// run the form here //--  
    newt:FormRun(form) 
     
    -- get the selected "item" (our pointer above)  
    atom ptr = newt:ListboxGetCurrent( listbox )  
				  
    -- fetch the index from the pointer  
    integer index = peek4s( ptr )  
				   
    -- display the result  
    printf( 1, "you selected: %s\n", fruits[index] )  
     
    newt:FormDestroy(form) 
    newt:Finished() 
end procedure 
main() 
 

This is the ex.err file: 
 
/home/ken/euphoria/euprogs/eunewt/demo/fruit_listbox.ex:57 in procedure main()  
subscript value 32880 is out of bounds, reading from a sequence of length 3  
    retval (from inlined routine 'Finished' at 213) = <no value> 
    retval (from inlined routine 'Init' at 6) = <no value> 
    fruits = { 
               {65'A',112'p',112'p',108'l',101'e',115's'}, 
               {66'B',97'a',110'n',97'a',110'n',97'a',115's'}, 
               {79'O',114'r',97'a',110'n',103'g',101'e',115's'} 
             } 
    form = 18612064 
    listbox = 18755504 
    buttonSubmit = 18620320 
    index = 3 
    ptr = <no value> 
    ptr = 16715776 
    index = 32880 
 
... called from /home/ken/euphoria/euprogs/eunewt/demo/fruit_listbox.ex:62  
 
 
Public & Export & Global & Local Variables 
 
 /home/ken/euphoria/include/std/memconst.e: 
    DEP_really_works = 0 
    use_DEP = 1 
    FREE_RID = 2 
    kernel_dll = <no value> 
    memDLL_id = <no value> 
    VirtualAlloc_rid = <no value> 
    VirtualLock_rid = <no value> 
    VirtualUnlock_rid = <no value> 
    VirtualProtect_rid = <no value> 
    GetLastError_rid = <no value> 
    GetSystemInfo_rid = <no value> 
 
 /home/ken/euphoria/include/std/memory.e: 
    edges_only = <no value> 
    check_calls = 1 
    VirtualFree_rid = <no value> 
 
 /home/ken/euphoria/include/std/types.e: 
    Defined_Sets = { 
                     {98'b',99'c',100'd',102'f',103'g',104'h',106'j',107'k', 
108'l',109'm',110'n',112'p',113'q',114'r',115's',116't',118'v',119'w',120'x', 
121'y',122'z',66'B',67'C',68'D',70'F',71'G',72'H',74'J',75'K',76'L',77'M', 
78'N',80'P',81'Q',82'R',83'S',84'T',86'V',87'W',88'X',89'Y',90'Z'}, 
                     {97'a',101'e',105'i',111'o',117'u',65'A',69'E',73'I', 
79'O',85'U'}, 
                     { 
                       {48'0',57'9'}, 
                       {65'A',70'F'}, 
                       {97'a',102'f'} 
                     }, 
                     {32' ',9,10,13,11,160}, 
                     { 
                       {32' ',47'/'}, 
                       {58':',63'?'}, 
                       {91'[',96'`'}, 
                       {123'{',126'~'} 
                     }, 
                     { 
                       {32' ',126'~'} 
                     }, 
                     { 
                       {32' ',126'~'}, 
                       {32' ',32' '}, 
                       {9,9}, 
                       {10,10}, 
                       {13,13}, 
                       {8,8}, 
                       {7,7} 
                     }, 
                     { 
                       {97'a',122'z'} 
                     }, 
                     { 
                       {65'A',90'Z'} 
                     }, 
                     { 
                       {48'0',57'9'}, 
                       {97'a',122'z'}, 
                       {65'A',90'Z'} 
                     }, 
                     { 
                       {48'0',57'9'}, 
                       {97'a',122'z'}, 
                       {65'A',90'Z'}, 
                       {95'_',95'_'} 
                     }, 
                     { 
                       {97'a',122'z'}, 
                       {65'A',90'Z'} 
                     }, 
                     { 
                       {0,127} 
                     }, 
                     { 
                       {0,31}, 
                       {127,127} 
                     }, 
                     { 
                       {48'0',57'9'} 
                     }, 
                     { 
                       {33'!',126'~'} 
                     }, 
                     { 
                       {0,255} 
                     }, 
                     {95'_'}, 
                     {1,0} 
                   } 
 
 /home/ken/euphoria/include/std/machine.e: 
    FREE_ARRAY_RID = 1 
    page_size = 4096 
 
 /home/ken/euphoria/euprogs/eunewt/demo/../newt.e: 
    libnewt = 16605808 
 

Any suggestions will be appreciated!

Kennneth Rhodes

5. Re: NEWT :: selecting an item from a listbox

• Posted by K_D_R Dec 26, 2012
• 1898 views

Still no joy.

http://openeuphoria.org/pastey/180.wc

7. Re: NEWT :: selecting an item from a listbox

• Posted by gbonvehi May 09, 2013
• 1766 views

Hi Ken,

Here you've a working example using pointers as you first tried: http://openeuphoria.org/pastey/216.wc

Of course, your solution is the correct one, but to prove you could store a pointer as data I got this example working.

The problem was that you allocated memory and got a pointer to it but that memory was set to autofree. As the pointer is "forgotten" by Euphoria and passed to Newt, Euphoria deallocates it as thinks it's not used anymore. So the key was to allocate the memory and not free it until the end.

By the way, I've just realized my code has a memory leak since I only free the selected's item memory. So be sure to check that if you're going to store pointers as data in the listboxes :)

Cheers,
Guillermo

PS: Relevant documentation: http://openeuphoria.org/docs/std_machine.html#_5596_allocate_data

9. Re: NEWT :: selecting an item from a listbox

• Posted by K_D_R May 12, 2013
• 1701 views

Here I have attempted to make a bit more generic eunewt listbox include file.

-- 
-- listbox.e 
-- Kenneth Rhodes 
-- wolfmanjacques@gmail.com 
-- simple newt-euphoria list box demo 
-- 
-- Newt for Euphoria by Greg Haberek 
-- https://bitbucket.org/ghaberek/eunewt/downloads/eunewt.zip 
-- 
-- http://gnewt.sourceforge.net/tutorial.html#toc1 
-- 
-- Demonstrates how to pass an integer "key" (sequence index) to the  
-- newt application which may be used to access a list box selection,  
-- instead of allowing the application to set an arbitrary pointer  
-- to the value selected. 
-- 
-- Comments illustrate the alternate method of using pointers. 
 
include edx/newt.e 
 
sequence list = {} 
sequence selection= " " 
 
integer centered_window_width, centered_window_height, 
	listbox_left_margin, listbox_top_margin, listbox_height, 
	button_left_margin, button_top_margin, 
	ll 
 
    centered_window_height = 18 
    centered_window_width = 45 
     
    listbox_height = 10 
    listbox_left_margin = 2 
    listbox_top_margin = 2 
     
    button_left_margin = 5 
    button_top_margin = centered_window_height -3 
 
 
 
procedure main() 
     
    newtComponent form,  
	listbox, 
	buttonSubmit -- not needed, if NEWT_FLAG_RETURNEXIT flag is used 
 
    newt:Init() 
    newt:Cls() 
     
    newt:CenteredWindow( 
			centered_window_width, 
			centered_window_height,     
			"Arrow up/down/right/Enter to Submit"  
			) 
     
    -- create a new list box  
    listbox = newt:Listbox(  
			    listbox_left_margin,  
			    listbox_top_margin,      
			    listbox_height,         
			    NEWT_FLAG_SCROLL   
--                              NEWT_FLAG_RETURNEXIT    
--                              does not require submit button, scrolling slider  
--                              is not shown 
			    )  
     
    --  loop through the items in the list sequence  
    --  add the items to the list box, assigning the 
    --  items sequence index as the "key", which would 
    --  by default be a pointer automatically assigned by 
    --  the application 
    for index = 1 to length(list) do  
      
     newt:ListboxAppendEntry(     
				listbox,         -- newt component 
				list[index],     -- text item 
				index            --<==== key, an integer, the sequence item index 
						 --      will now be returned, instead of a 
						 --      pointer assigned by the application                                         
			     ) 
     
    end for 
     
    -- not needed if  NEWT_FLAG_RETURNEXIT flag is used 
    buttonSubmit = newt:Button(  
				button_left_margin,  
				button_top_margin,  
				"Submit"  
				)    
     
    form = newt:Form( NULL, NULL, 0 ) 
    newt:FormAddComponents( form, { listbox, buttonSubmit } ) 
--  newt:FormAddComponents( form, { listbox})  -- if NEWT_FLAG_RETURNEXIT flag is used 
     
    --// run the form here //--  
    newt:FormRun(form) 
     
    -- get the selected "item" 
    atom index = newt:ListboxGetCurrent( listbox ) 
     
    newt:FormDestroy(form) 
    newt:Finished() 
 
    selection = sprintf("%s", {list[index]}) 
end procedure 
 
public function listbox( sequence items ) 
    list = items 
    ll = length(list) 
    for i = 1 to ll do 
	if length(list[i])>centered_window_width then 
	    centered_window_width = length(list[i]) + 6 
	end if 
    end for 
main() 
return selection 
end function