Deselect/Select items programmatically in a ListBox
lazarus / 31-LCL

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maurobio · 2025-04-09 11:55

Dear ALL,

In a form I have a multi-select listbox and an edit control. I want to
programmatically select an item in the listbox corresponding to the
item number typed in the edit control, but I also want to select more
than one item if a '/' is typed in the edit control. so for example if
I type 1/2 the first two items in the list box should be selected.

I have not been able to get the latter part done; is this not possible
with multi-select listboxes?

My test code is attached, could someone out there give me a hand?

Many thanks in advance!

With best regards,

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Zvoni · 2025-04-09 12:11

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Edit1Change(Sender: TObject);Var  s:String;  a:Array Of
String;  i:Integer;begin  If Edit1.Text<>'' Then    Begin     
s:=Edit1.Text;      a:=s.Split('/');      ListBox1.ClearSelection;   
 For i:=Low(a) To High(a) Do If a[i]<>'' Then
ListBox1.Selected[a[i].ToInteger-1]:=True;    end;end;               
No defense whatsoever. No checks on only numeric entries and "/"
Your Job

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maurobio · 2025-04-09 12:29

Hi, Zvoni!

Thanks, but this produces the same results I obtained with my flawed
test code.

I want to have all items selected which correspond to the numbers
typed in the listbox: so, for example, if I type 1/2, the first two
items should be selected and so on.

Currently, both my code and yours select only the last item whose
number is typed in the edit control.

With best regards,

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Zvoni · 2025-04-09 12:33

Quote from: maurobio on April 09, 2025, 02:29:01 pmHi, Zvoni!

Thanks, but this produces the same results I obtained with my flawed
test code.

I want to have all items selected which correspond to the numbers
typed in the listbox: so, for example, if I type 1/2, the first two
items should be selected and so on.

Currently, both my code and yours select only the last item whose
number is typed in the edit control.

With best regards,
Err.... no?
I tested it with 5 Items in my Testproject.
Entering"2/3/5" exactly those items were selected, and any other items
selected before were "deselected"

And as i said: No defense whatsoever if User enters crap

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maurobio · 2025-04-09 12:43

Hi, Zvoni!

Strange, really... but after compiling and running your test project,
it worked fine!

I will implement myself the defences against bad inputs (in fact part
of them are already implemented in my test code).

Thank you very much!

With warmest regards,

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Zvoni · 2025-04-09 13:19

Quote from: maurobio on April 09, 2025, 02:43:33 pmHi, Zvoni!

Strange, really... but after compiling and running your test project,
it worked fine!

I will implement myself the defences against bad inputs (in fact part
of them are already implemented in my test code).

Thank you very much!

With warmest regards,
Beware: My logic is not fully formulated.
It works, if you only have 9 or less items in the Listbox. The Moment
you have 10 or more my sample above doesn't work anymore.
Think about it: How will the Edit-Box know, if you enter "1" (My Code
executes and selects Item1) that there is still a "3" coming (because
you want to select Item 13, in that case DE-Selecting Item1 and
selecting Item13)?

To fully and correctly process the entry,  you'll probably have to
switch from OnChange to OnKeyDown or to OnKeyPress (or a combination
of all 3)
legal Characters: Digits and "/"
in OnKeyDown/OnKeyPress you "wait" for the "/" being entered before
jumping into my code (split, for-loop, if-then-else).
And even that is not bullet-proof, since your Edit-Box will never know
when you're done.

There is still more thinking to do