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Programming => General => Topic started by: noszone on June 21, 2021, 07:00:29 am

Title: Populate combobox with values and custom indexes
Post by: noszone on June 21, 2021, 07:00:29 am

I am quite new in objects and pointers, can anyone please advise how to populate combobox with values and custom indexes. For example:

Code: Pascal  [Select][+][-]

1. cb1.Items.AddObject(value1, customIndex25);
2. cb1.Items.AddObject(value2, customIndex100);

So when I will use

Code: Pascal  [Select][+][-]

1. cb1.ItemIndex

it will return as following:
25
100

I've tried with objects, but no luck (it not returning an ID).

Thanks.

Title: Re: Populate combobox with values and custom indexes
Post by: egsuh on June 21, 2021, 07:12:13 am

Following example works.  You cannot customize indexex of items because they are TStrings property.

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. begin
3.    combobox1.items.clear;
4.    Combobox1.AddItem('Item A', TObject(12));
5.    Combobox1.AddItem('Item B', TObject(25));
6.    Combobox1.AddItem('Item C', TObject(33));
7. end;
8.  
9. procedure TForm1.ComboBox1Change(Sender: TObject);
10. var
11.   Index: Integer;
12.   s: string;
13. begin
14.   Index := ComboBox1.ItemIndex;
15.   if Index <> -1 then begin
16.     s := IntTostr(Integer(ComboBox1.Items.Objects[Index]));
17.     ShowMessage(s)
18.   end
19.   else
20.     ShowMessage('Nothing Selected');
21. end;
22.  

Title: Re: Populate combobox with values and custom indexes
Post by: noszone on June 21, 2021, 07:24:25 am

Incredible, this is exactly what I looked for, thanks.

Title: Re: Populate combobox with values and custom indexes
Post by: wp on June 21, 2021, 11:20:14 am

Quote from: egsuh on June 21, 2021, 07:12:13 am

Code: Pascal  [Select][+][-]

1.     s := IntTostr(Integer(ComboBox1.Items.Objects[Index]));
2.  

Be careful, this code will crash in a 64-bit application where pointers (Combobox.Items.Objects[]) and integers have different size. Use PtrUInt or PtrInt rather than integer which are integer types having the same size as a pointer in any OS:

Code: Pascal  [Select][+][-]

1.     s := IntTostr(PtrUInt(ComboBox1.Items.Objects[Index]));
2.  

Title: Re: Populate combobox with values and custom indexes
Post by: egsuh on June 21, 2021, 11:28:16 am

Quote

Use PtrUInt or PtrInt rather than integer

Oh yes. This is really important information. I experienced some problem in similar occasion. Thank you very much.

Title: Re: Populate combobox with values and custom indexes
Post by: noszone on June 21, 2021, 01:35:27 pm

Such a pro tip, always learning something new :D.