Interfaces composition

[Ildefonso Martínez Marchena]

I am trying to compose interfaces i would like to know if dspring could help me to deal with that

p.e.

GlobalContainer.RegisterType<TTT>.Implements<Intf1>.Implements<Intf2>;

and then

var

 av : Intf1;

begin

 av := Resolve<TTT>;

 ...

 and get Intf2 from av?

I dont want to use extensive use of queryinterface(...)

Best regards

ilde

[Glienke, Stefan]

You can use the as operator:

 

var

  intf1: IIntf1;

  intf2: IIntf2;

begin

  intf1 := Resolve<IIntf1>;

  intf2 := intf2 as IIntf2;

 

Attention! The compile generates a call to System._IntfCast which throws an exception if QueryInterface does return 0.

So it is not the same behavior like it is for classes where an as returns nil if the instance does not inherit from the given class.

 

So I guess what you asking for is some kind of Supports method that only checks the interfaces registered with the container?

Otherwise I cannot think of any way how something the container could provide would be any shorter than a Supports call.

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[Ildefonso Martínez Marchena]

Thank you...

that worked fine but i think that situation doesnt work with implemens directive

if i have

TTT = class(TInterfacedObject, IIntf1, IIntf2)

private

  fIntf1 : IIntf1;

public

   property Intf1impl : IIntf1 read fIntf1 write fIntf1 implements IIntf1;

end

i cant get Intf2 from Intf1 :( .... i think i should declare all interface methods inside TTT and code all against fIntf1 :( :(  lossing the power of implments directive

In other side i should store main instance as IInterface type and change all my objects references from IIntf1 to IInterface and assign to IInterrface var the main object...unless I'm wrong which is very common in me :p

All the best

ilde

2013/2/8 Glienke, Stefan <SGli...@aagon.com>

[Glienke, Stefan]

In your example the instance behind the fIntf1 field has no clue about the TTT instance it is part of.

 

So you need something to delegate QueryInterface back to the container it is part of. System.TAggregatedObject is for this case but it has some problems as it does not work when used as interface reference itself as it does not only delegate the QueryInterface to its container but also the _AddRef and _Release calls causing memory leaks (as reported 7 years ago: http://qc.embarcadero.com/wc/qcmain.aspx?d=24316 – and still open ^^)

 

So here is what I wrote:

 

type

  IAggregation = interface

    ['{566FCC7E-6E0D-4401-BE34-61C0C6F6C125}']

    function GetContainer: IInterface;

    procedure SetContainer(const Value: IInterface);

    property Container: IInterface read GetContainer write SetContainer;

  end;

 

  TAggregation = class(TInterfacedObject)

  private

    fContainer: Pointer;

  protected

    function GetContainer: IInterface;

    procedure SetContainer(const Value: IInterface);

    function QueryInterface(const IID: TGUID; out Obj): HResult; stdcall;

  public

    constructor Create(Container: IInterface); overload;

    property Container: IInterface read GetContainer write SetContainer;

  end;

 

constructor TAggregation.Create(Container: IInterface);

begin

  fContainer := Pointer(Container);

end;

 

function TAggregation.GetContainer: IInterface;

begin

  Result := IInterface(fContainer);

end;

 

function TAggregation.QueryInterface(const IID: TGUID; out Obj): HResult;

begin

  Result := inherited QueryInterface(IID, Obj);

  if Result = E_NOINTERFACE then

    Result := IInterface(fContainer).QueryInterface(IID, Obj);

end;

 

procedure TAggregation.SetContainer(const Value: IInterface);

begin

  fContainer := Pointer(Value);

end;

 

now you can write code like this:

 

type

  IFoo = interface

    ['{3E53FECD-A143-4BE1-B940-115979244A5A}']

  end;

 

  IBar = interface(IAggregation)

    ['{FA50D22B-FBC8-4B20-8F21-CD8B168DEDD0}']

  end;

 

  TBar = class(TAggregation, IBar)

  end;

 

  TFoo = class(TInterfacedObject, IFoo, IBar)

  private

    fBar: IBar;

    procedure SetBar(const Value: IBar);

  protected

    property Bar: IBar read fBar write SetBar implements IBar;

  end;

 

procedure TFoo.SetBar(const Value: IBar);

begin

  if Assigned(fBar) then

    fBar.Container := nil;

  fBar := Value;

  if Assigned(fBar) then

    fBar.Container := Self;

end;

 

var

  obj: TFoo;

  foo: IFoo;

  bar: IBar;

  foo2: IFoo;

begin

  // simulate container creating the object

  obj := TFoo.Create;

  obj.Bar := TBar.Create;

  foo := obj;

 

  bar := foo as IBar;

  foo2 := bar as IFoo;

end;