delphi component with a collection of TPictures

Question

I'm trying to create a VCL component like TImage, that lets me add a variable amount of different sized TPictures. The Goal is to be able to assign that number of TPictures through the VCL editor in the property list.

delphi component property: TObjectList<TPicture> here we came to the conclusion, that a TCollection with TCollectionItems should be used. This is what I'm trying to do now, but as many times before i end up with the compiler error: "Published property 'Pictures' can not be of Type ARRAY" in this line: property Pictures[Index: Integer]: TPic read GetPic write SetPic;

unit ImageMultiStates;

interface

uses
  Vcl.Graphics, Vcl.StdCtrls, System.SysUtils, System.Classes, Vcl.Controls, Vcl.ExtCtrls, Forms, Generics.Collections;

type

  TPic = class(TCollectionItem)
  private
    FPicture: TPicture;
  public
    procedure Assign(Source: TPersistent); override;
    constructor Create(Collection: TCollection); override;
    destructor Destroy; override;
  published
    property Picture: TPicture read FPicture write FPicture;
  end;

  TPictures = class(TCollection)
  private
    function GetPic(Index: Integer): TPic;
    procedure SetPic(Index: Integer; APicture: TPic);
  public
    constructor Create;
  published
    property Pictures[Index: Integer]: TPic read GetPic write SetPic;
  end;

  TImageMultiStates = class(TImage)
  private
    FPictures: TPictures;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    procedure Activate(Index: Integer);
  end;

procedure Register;

implementation

constructor TPic.Create(Collection: TCollection);
begin
  inherited Create(Collection);
end;

destructor TPic.Destroy;
begin
  FPicture.Free;
  inherited Destroy;
end;

procedure TPic.Assign(Source: TPersistent);
begin
  FPicture.Assign(Source);
end;


constructor TPictures.Create;
begin
  inherited Create(TPic);
end;

procedure TPictures.SetPic(Index: Integer; APicture: TPic);
begin
  Items[Index].Assign(APicture);
end;

function TPictures.GetPic(Index: Integer): TPic;
begin
  Result := TPic(inherited Items[Index]);
end;


constructor TImageMultiStates.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
end;

destructor TImageMultiStates.Destroy;
begin
  FPictures.Free;
  inherited Destroy;
end;

procedure TImageMultiStates.Activate(Index: Integer);
begin
  Picture.Assign(FPictures.Items[Index]);
end;

procedure Register;
begin
  RegisterComponents('Standard', [TImageMultiStates]);
end;

end.

Since noone seems to expect this error to be thrown, maybe it's related to my installed components? I used the internal GetIt Package-Manager to install the Jedi Code Library 2.8, Jedi Visual Component Library and PNGComponents 1.0. I guess that's about it as far as TImage-related components are concerned. Maybe one of these overrides some of my TImage contents with funky stuff...

Answer 1

I experimented a little and derived a TPicturePanel from TPanel. It has a Pictures property, which is a TPictures, a descendant of TOwnedCollection and which contains TPics. Each TPic has a Picture property. I can install this component, and it allows me to edit the Pictures collection using the so called Collection editor, which allows you to add or remove TPic instances. If you select a TPic in the Collection editor, you can assign a picture to its Picture property, i.e. load from file, etc.

Here is the working code for TPicturePanel. You can model your component after this:

unit PicturePanels;

interface

uses
  System.SysUtils, System.Classes, Vcl.Controls, Vcl.ExtCtrls, Vcl.Graphics;

type
  TPic = class(TCollectionItem)
  private
    FPicture: TPicture;
    procedure SetPicture(const Value: TPicture);
  public
    procedure Assign(Source: TPersistent); override;
    constructor Create(AOwner: TCollection); override;
    destructor Destroy; override;
  published
    property Picture: TPicture read FPicture write SetPicture;
  end;

  TPictures = class(TOwnedCollection)
  private
    function GetItem(Index: Integer): TPic;
    procedure SetItem(Index: Integer; const Value: TPic);
  public
    constructor Create(AOwner: TPersistent);
    property Items[Index: Integer]: TPic read GetItem write SetItem;
  end;

  TPicturePanel = class(TPanel)
  private
    FPictures: TPictures;
    procedure SetPictures(const Value: TPictures);
  published
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    property Pictures: TPictures read FPictures write SetPictures;
  end;

procedure Register;

implementation

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

{ TPicturePanel }

constructor TPicturePanel.Create(AOwner: TComponent);
begin
  inherited;
  FPictures := TPictures.Create(Self);
end;

destructor TPicturePanel.Destroy;
begin
  FPictures.Free;
  inherited;
end;

procedure TPicturePanel.SetPictures(const Value: TPictures);
begin
  FPictures.Assign(Value);
end;

{ TPic }

procedure TPic.Assign(Source: TPersistent);
begin
  inherited;
  if Source is TPic then
    FPicture.Assign(TPic(Source).FPicture);
end;

constructor TPic.Create(AOwner: TCollection);
begin
  inherited;
  FPicture := TPicture.Create;
end;

destructor TPic.Destroy;
begin
  FPicture.Free;
  inherited;
end;

procedure TPic.SetPicture(const Value: TPicture);
begin
  FPicture.Assign(Value);
end;

{ TPictures }

constructor TPictures.Create(AOwner: TPersistent);
begin
  inherited Create(AOwner, TPic);
end;

function TPictures.GetItem(Index: Integer): TPic;
begin
  Result := inherited GetItem(Index) as TPic;
end;

procedure TPictures.SetItem(Index: Integer; const Value: TPic);
begin
  inherited SetItem(Index, Value);
end;

end.