TComboBox: How can I remove duplicates from list?

[AMJF]

I have written a routine that scans the files in a folder and adds them to the TComboBox control on my form, but while I can sort the items alphabetically, I haven't found the means of removing duplicate entries added to the control.

Is there a means of doing this, or will I have to resort to a TStringList and then copy it over to the TComboBox to achieve what I want?

[h-elsner]

I don't let them in.

Code: Pascal  [Select][+][-]

1. procedure Merkliste(ml: TComboBox; maxNumberItems: integer);
2. begin                                              {fill a DropDownList}
3.   if (ml.Text<>'') and
4.      (ml.Items.IndexOf(ml.Text)<0) then            {not in list yet}
5.     ml.Items.Insert(0, ml.Text);
6.   if ml.Items.Count>MaxNumberItems then               {limit the number of entries}
7.     ml.Items.Delete(MaxNumberItems);
8. end;
9.  

However, TComboBox is TStrings and has all on-board to delete, insert and so on. No need for a StringList.

br HE

[AMJF]

I clean forgot about IndexOf to see if the string was already there or not before addition. Have made the changes, program works fine now. Thanks!

[krexon]

Code: Pascal  [Select][+][-]

1. var
2.   SL: TStringList;
3. begin
4.   ComboBox1.Items.BeginUpdate;
5.   try
6.     SL := TStringList.Create;
7.     try
8.       SL.Sorted := True; // Required for Duplicates to work
9.       SL.Duplicates := dupIgnore;
10.       SL.AddStrings(ComboBox1.Items);
11.       ComboBox1.Items.Assign(SL);
12.     finally
13.       SL.Free;
14.     end;
15.   finally
16.     ComboBox1.Items.EndUpdate;
17.   end;
18. end;

[JuhaManninen]

This is slightly off-topic, not related to only ComboBoxes, but I would like to advertise the unit LookupStringList in LazUtils package.
Class TLookupStringList is an unsorted StringList with a fast lookup feature.
Internally it uses a balanced tree container (TStringMap) to store the strings again which is then used for Contains, IndexOf and Find methods.
It is very memory efficient, because:
1. Strings have reference count and lazy copy semantics. It means only a reference to a string is copied to the other container.
2. A balanced tree is memory efficient compared to a hash map.

This class is useful when you must preserve the order in list, but also need to do fast lookups to see if a string exists, or you must prevent duplicates.

There is also a function Deduplicate().

[AlexTP]

Juha,
Thanks for that info!
Useful.
Why don't you give link to https://wiki.lazarus.freepascal.org/LazUtils#TLookupStringList ?

[JuhaManninen]

Why don't you give link to https://wiki.lazarus.freepascal.org/LazUtils#TLookupStringList ?

I forgot that wiki page. It's information is rather limited. The page is about the whole LazUtils but it lists only 2 items.