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TCollection The Class for Master Detail Relations (Views: 101)


Problem/Question/Abstract:

Getting A master Detail Relation in a component on a way it's easely streamed.
Using a TStream Class Decendant

Answer:

The collection Class is one of my favorit when it comes to storing multiple Data with one component its even posible to include the Collection in its own item making it useful for recursion (The Collection Can have a item withs can hold a other collection.

If you want the standard Editor for Collections u have to use a TOwnedCollection i think its ijn the unit Classes from delphi 4 but if u have D3 u need to Make that class first like this

TOwnedCollection = class(TCollection)
private
  FOwner: TPersistent;
protected
  function GetOwner: TPersistent; override;
public
  // Fil in the AOwner in The Fowner proeprty on the Create Constructor .
  constructor Create(AOwner: TPersistent; ItemClass: TCollectionItemClass);
end;

Heres a Example Of a collection That does that

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TMyCollection = class(TOwnedCollection)

  end;

  TMyCollectionItem = class(TCollectionItem)
  private
    FANummer: Integer;
    FAString: string;
    FMoreCollections: TMyCollection;
    procedure SetANummer(const Value: Integer);
    procedure SetAString(const Value: string);
    procedure SetMoreCollections(const Value: TMyCollection);
  public
    constructor Create(Collection: TCollection); override;
    destructor Destroy; override;
  published
    property AString: string read FAString write SetAString;
    property ANummer: Integer read FANummer write SetANummer;
    property MoreCollections: TMyCollection read FMoreCollections write
      SetMoreCollections;
  end;

  TCollectionWrapper = class(TComponent)

  private
    FCollection: TMyCollection;
    procedure SetCollection(const Value: TMyCollection);
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;

  published
    property Collection: TMyCollection read FCollection write SetCollection;
  end;

implementation

{ TMyCollectionItem }

constructor TMyCollectionItem.Create(Collection: TCollection);
begin
  inherited;
  FMoreCollections := TMyCollection.Create(self, TMyCollectionItem);
end;

destructor TMyCollectionItem.Destroy;
begin
  FMoreCollections.free;
  inherited;

end;

procedure TMyCollectionItem.SetANummer(const Value: Integer);
begin
  FANummer := Value;
end;

procedure TMyCollectionItem.SetAString(const Value: string);
begin
  FAString := Value;
end;

procedure TMyCollectionItem.SetMoreCollections(const Value: TMyCollection);
begin
  FMoreCollections := Value;
end;

{ TCollectionWrapper }

constructor TCollectionWrapper.Create(AOwner: TComponent);
begin
  inherited;
  FCollection := TMyCollection.Create(self, TMyCollectionItem);
end;

destructor TCollectionWrapper.Destroy;
begin
  FCollection.free;
  inherited;

end;

procedure TCollectionWrapper.SetCollection(const Value: TMyCollection);
begin
  FCollection := Value;
end;

end.

This is how you could addres it Run time

procedure TForm1.Button1Click(Sender: TObject);
var
  ACollection: TCollectionWrapper;
begin
  ACollection := TCollectionWrapper.Create(Self);
  try
    // Default add gives u a TCollectionItem So u need to cast it
    with TMyCollectionItem(ACollection.Collection.Add()) do
    begin
      AString := 'Hallo';
      ANummer := 5;
      MoreCollections.add;

    end;

  finally
    ACollection.Free;
  end;
end;

If you register this component u will be able to use the default Collection Editor Design time

Component Download: http://www.xs4all.nl/~suusie/Pieter/Programs/CollectionComponent.zip

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