Releasing interface with inner interfaces issue

Question

I have a code here:

unit Unit1;

interface

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

type
  IInnerTest = interface (IInterface)
    procedure DoSth;
  end;

  TRekScannerData = record
    Source: Integer;
    Device: IInnerTest;
  end;

  ITest = interface (IInterface)
    procedure DoSth;
  end;

  ATest = class(TInterfacedObject, ITest)
  private
    FInner: Array of TRekScannerData;
  public
    procedure DoSth;
    constructor Create();
    Destructor Destroy();override;
  end;

  AInnerTest = class (TInterfacedObject, IInnerTest)
  private
    FMainInt: ITest;
  public
    constructor Create(MainInt: ITest);
    procedure DoSth;
    Destructor Destroy();override;
  end;

  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  test: ITest;

implementation

{$R *.dfm}

{ ATest }

constructor ATest.Create;
begin
  SetLength(FInner, 1);
  FInner[0].Device := AInnerTest.Create(self);
  //<----- Here is the reason. Passing main interface to the inner interface.
end;

destructor ATest.Destroy;
begin
  beep;
  inherited;
end;

procedure ATest.DoSth;
begin
  //
end;

{ AInnerTest }

constructor AInnerTest.Create(MainInt: ITest);
begin
  FMainInt := MainInt;
end;

destructor AInnerTest.Destroy;
begin
  beep;
  inherited;
end;

procedure AInnerTest.DoSth;
begin
  //
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  test := ATest.Create;
  test.DoSth;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  test := nil;
end;

end.

The problem is that Destroy is not called when test is assigned to nil;

I would like to release all the inner interfaces by one statement ... Is it possible? or do I need to prior to nil destroy all inner structures by using another method?

EDIT

The class structure is as follows:

Var x = ITest(ATest class) has ->
  Inner Interface: IInnerTest(AInnerTest class) which has reference to:
    ITest(ATest class)

Nil'ing x doesn't release all structure ...

Answer 1

You have a circular reference. Your implementation of IInnerTest holds a reference to ITest. And your implementation of ITest holds a reference to IInnerTest. And this circular reference means that the interface reference count can never go to zero.

The normal solution to this issue to to use a weak reference. Some useful links:

• "Weak reference": down to earth explanation needed
• http://www.finalbuilder.com/Resources/Blogs/PostId/410/WeakRefence-in-Delphi-solving-circular-interfac.aspx
• http://delphisorcery.blogspot.co.uk/2012/06/weak-interface-references.html