Delphi 接口中的引用计数

Question

基本问题。在 Button1Click 中，我创建了一个接口对象。创建后引用计数为0。我将对象作为参数传递。引用计数在函数结束时增加、减少，当它为 0 时，它被销毁。我想念什么吗？当我首先创建对象时，我在想引用计数应该是 1？ lListFilter 没有持有对象的引用？

type
    IPersistentListFilter = Interface(IInterface)
        ['{57cdcf89-60ee-4b3c-99fd-177b4b98d7e5}']
        procedure IncludeObject;
end;

procedure FillList(AFilter : IPersistentListFilter);

type
TPersistentListFilter = class(TInterfacedObject, IPersistentListFilter)
    procedure IncludeObject;
    constructor Create;
    destructor Destroy; override;
end;

implementation

procedure FillList(AFilter: IPersistentListFilter);
begin
     AFilter.IncludeObject;
end;

constructor TPersistentListFilter.Create;
begin
    inherited;
end;

destructor TPersistentListFilter.Destroy;
begin
    inherited;
end;

procedure TPersistentListFilter.IncludeObject;
begin
    // do nothing
end;

procedure TForm8.Button1Click(Sender: TObject);
var
    lListFilter: TPersistentListFilter;
begin
    lListFilter := TPersistentListFilter.Create;
    // ref count is 0
    FillList(lListFilter);
    // lListFilter has been destroyed
    FillList(lListFilter);  // --> error
end;

Answer 1

在 Button1Click 中，lListFilter 被声明为 TPersistentListFilter 的实例，而不是 IPersistentListFilter。因此，在创建 lListFilter 时不会发生引用计数。

lListFilter 需要声明为 IPersistentListFilter:

procedure TForm8.Button1Click(Sender: TObject);
var
  lListFilter: IPersistentListFilter;
begin
  lListFilter := TPersistentListFilter.Create;
  // ref count will be 1

  // ref count will go to 2 during call to FillList
  FillList(lListFilter);

  // ref count will be back to 1

  // ref count will go to 2 during call to FillList
  FillList(lListFilter);  

  // ref count will be back to 1

end;   // ref count will go to 0 as lListFilter goes out of scope 
       //    and is destroyed.

Delphi 接口中的引用计数

Reference counting in Delphi Interfaces

delphi

reference-counting