Cannot get ComboBox selected item value

Question

I am using this code at the moment. I need to get the String value of the selected item of a ComboBox:

procedure TForm5.BitBtn5Click(Sender: TObject);
var c,k,t,g: string;
begin

 //Get the name of the items
 c := ComboBox1.Items[ComboBox1.ItemIndex];
 k := ComboBox2.Items[ComboBox2.ItemIndex];
 t := ComboBox3.Items[ComboBox3.ItemIndex];
 g := ComboBox4.Items[ComboBox4.ItemIndex];

 //Show it
 ShowMessage(c);

 end;

The ComboBoxes have items inside as you can see here because I fill them in an onCreate event of the Form5. When I press the BitBtn5 I have an error like this:

enter image description here

I have googled my problem and I have found the code is the same, but I have that error. Do you have any idea? (I am using lazarus 1.2.4)

It's *safer* (if that is your aim) to get those values simply by `ComboBox.Text`. — TLama, Sep 04 '14 at 21:50
@TLama I didn't think about it, it's so simply... It works, thank you. But I still don't know why my code is wrong — Alberto Rossi, Sep 04 '14 at 21:51
Remove 'delphi' tag, because it's misleading. Lazarus raises an exception when item index is -1, Delphi does not. — Sertac Akyuz, Sep 04 '14 at 21:53
Probably, some (or all) `ComboBoxN.ItemIndex` returns -1 (item not selected) — Abelisto, Sep 04 '14 at 21:54

score 2 · Accepted Answer · answered Sep 04 '14 at 21:55

2

At least one of your ComboBox's item index is -1. Set them to a valid index at form creatiton, eg:

ComboBox1.ItemIndex := 0;

answered Sep 04 '14 at 21:55

Sertac Akyuz

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So is this an "exception" because I am using Lazarus? (It works now) – Alberto Rossi Sep 04 '14 at 21:57
1

@Alberto - Well, I wouldn't put it that way. This is an exception because item index is not valid is more like it I guess. :) – Sertac Akyuz Sep 04 '14 at 21:58
1

@Alberto - You are welcome. To be frank I only checked the Win32 widget set. I don't actually know if other widget sets are doing the same check and raising the exception. For Win32, exception is raised in 'TWin32ListStringList.Get' function. – Sertac Akyuz Sep 04 '14 at 23:56

score 1 · Answer 2 · answered Aug 04 '15 at 13:42

I'm using Lazarus 1.4.2. The problem is that property ItemIndex is not updating when selecting items from ComboBox. To force this index to get updated I just placed some dummy code (that is accessing the ItemIndex) in OnChange event of ComboBox (see below). Then I can read ItemIndex from other places, and the value is correct.

procedure TForm1.ComboBoxChange(Sender: TObject);
var
  i: integer;
begin
  i := ComboBox.ItemIndex;
end;

I just encountered this problem now and I didn't find a proper solution on the internet. My post is very late but I hope this will help others.

Cannot get ComboBox selected item value

2 Answers2

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