Listbox with String Key
lazarus / 8-Other

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BenJones · 2013-05-25 18:08

With a listview control in VB I remember when you added items you
could also add a key, but in a list box this is not possible unless
you do a little coding, anyway I remember I needed something in VB.NET
for adding keys to a normal listbox and combo box, and got around the
problem by doing a tiny class and added it as an object.

Anyway I thought why not try and do the same thing in lazarus as you
can also add objects. Anyway this is what Came up with a tiny bit of
code to allow you to also add key to list box, my key is added as
string but you can change the data type if you like.
Hope this maybe of some help to someone.

Start a new project.
Next we create the smalll class that will house our value and key
add a unit to your project call it LstItem

Add the code below to the class

Code: [Select]unit LstItem;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils;

type
  TLstItem = class
  private
    fName, fKey: string;
  public
    constructor Create(const Caption, Key: string);
    property Caption : string read fName;
    property Key : string read fKey;
  end;

implementation

constructor TLstItem.Create(const Caption,Key : string);
begin
   fName := Caption;
   fKey := Key;
end;

end.
Ok add the class to your form uses
Next add a listbox to the form, use this code below that will add a
new item to the listbox.

Code: [Select]ListBox1.Items.AddObject('Apples',
TLstItem.Create('Apples', 'Fruit'));
As you can see we used our class to enable us to have a key Fruit
To get the key value of a selected item just use this code:

Code: [Select]procedure TForm1.ListBox1Click(Sender: TObject);
var
  t: TLstItem;
begin
  t := ListBox1.Items.Objects[ListBox1.ItemIndex] as TLstItem;
  //Show caption and key.
  ShowMessage(t.Caption);
  ShowMessage(t.Key);
end;

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howardpc · 2013-05-25 20:49

I don't think your TLstItem class needs the FName field. You're
duplicating storage already provided in the the Listbox's Items,
doubling memory use unnecessarily.

Another approach would be to introduce a class helper for TListBox as
in the following example in which a button and a listbox are dropped
onto the main form:

Code: [Select]unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Forms, Dialogs, StdCtrls;

type

  { TListBoxKeysHelper }

  TListBoxKeyHelper =  class helper for TListBox
  private
    function GetKey(anItem: integer): string;
    public
      procedure SetKey(anItemIndex: integer; const aKey: string);
      property Key[anItem: integer] : string read GetKey;
    end;

  { TForm1 }

  TForm1 = class(TForm)
    btnSetListBoxKey: TButton;
    ListBox1: TListBox;
    procedure btnSetListBoxKeyClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  end;


var
  Form1: TForm1;

implementation

{ TForm1 }

procedure TForm1.btnSetListBoxKeyClick(Sender: TObject);
begin
  ListBox1.setkey(0, '1');
  ListBox1.setkey(1, '2');
  ListBox1.setkey(1, '3');
  ShowMessageFmt('Item[1] has key %s',[ListBox1.Key[1]]);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ListBox1.Items.AddStrings(['one','two','three']);
end;

{ TListBoxKeysHelper }

function TListBoxKeyHelper.GetKey(anItem: integer): string;
begin
  Result:= '';
  if Items.Count=0 then Exit;
  if Items.Objects[anItem] <> nil
   then Result := string(Items.Objects[anItem]);
end;

procedure TListBoxKeyHelper.SetKey(anItemIndex: integer; const aKey:
string);
begin
  if (anItemIndex > -1) and (anItemIndex < Items.Count)
   then Items.Objects[anItemIndex] := TObject(akey);
end;

{$R *.lfm}

end.

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BenJones · 2013-05-26 02:08

Thanks for the heads up howardpc, Thanks for example to, I keep it in
my sniplet manager.