How to impliment a stringlist property in a custom delphi component?

Question

I am creating my first custom Delphi component. Its basically a custom Tpanel with header and lines text displayed on it.

I want to be able to add multiple lines text using a stringlist.

When testing the component I cannot get the text lines to display on the panel when adding lines: NewLinesText.add('line1 text')

It does however work when I create and populate a new stringlist at runtime and then assign it to my control : controlPanelitem.NewLinesText = MyNewStringlist

I want to be able to add lines like this: NewLinesText.add('line1 text')

I am using Delphi 7 professional on WinXP. See code below.

Any help would be appreciated!


unit ControlPanelItem;

interface

uses
  SysUtils, Classes, Controls, ExtCtrls, Graphics, AdvPanel, StdCtrls,
  Windows,Forms,Dialogs;

type
  tControlPanelItem = class(TAdvPanel)
  private
    fLinesText : TStrings;
    procedure SetLinesText(const Value: TStrings);
    procedure SetText;
  protected
  public
    constructor Create(AOwner : TComponent); override;
    destructor Destroy; override;
  published
    property NewLinesText  : TStrings read FLinesText write SetLinesText;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('Samples', [tControlPanelItem]);
end;

constructor tControlPanelItem.Create(AOwner: TComponent);
begin
  inherited;
  fLinesText := TStringList.Create;
end;

destructor tControlPanelItem.Destroy;
begin
  fLinesText.Free;
  inherited;
end;

procedure tControlPanelItem.SetLinesText(const Value: TStrings);
begin
  fLinesText.Assign(value);
  SetText;
end;

procedure tControlPanelItem.SetText;
var
   count : Integer;
begin
 for count := 0 to fLinesText.Count - 1 do
  ShowMessage(fLinesText.strings[count]);

end;

end.

Andreas Rejbrand Andreas Rejbrand · Accepted Answer · 2010-10-29T09:28:07

You should do

procedure SetLines(Lines: TStrings);
begin
  FLinesText.Assign(Lines);
  // Repaint, update or whatever you need to do.
end;

You may also need to set the OnChange property of the FLines (do this in the constructor of your custom control, as soon as you have created it). Set it to any TNofifyEvent-compatible (private or protected, I guess) procedure of your component. In this procedure, you can do the repainting, updating etc. you need.

That is, do

constructor TControlPanelItem.Create(AOwner: TComponent);
begin
  inherited;
  FLinesText := TStringList.Create;
  TStringList(FLinesText).OnChange := LinesChanged;
end;

procedure TControlPanelItem.LinesChanged(Sender: TObject);
begin
  // Repaint, update or whatever you need to do.
end;

How to impliment a stringlist property in a custom delphi component?

1 Answers