class(TInterfacedObject) 是否需要 Delphi 中的析构函数?

Does class(TInterfacedObject) need a destructor in Delphi?

我 运行 在这种情况下 Destroy() 永远不会被调用。

unit Unit2;

interface

type

// Interface
ITest = Interface(IInterface)
 function IsTrue() : Boolean;
end;

TmyClass = class(TInterfacedObject, ITest)
  public
    // Interface implementation
    function IsTrue() : Boolean;

    constructor Create();
    destructor Destroy(); override;
end;

implementation

constructor TmyClass.Create();
begin
  inherited Create();
end;

destructor TmyClass.Destroy();
begin
  inherited Destroy();
end;

published
  // Property
  property IsItTrue: Boolean read IsTrue;
end.

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, 
  System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, 
  Vcl.Dialogs, Vcl.StdCtrls, unit2;

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

var
  Form1: TForm1;
  fMyClass: TmyClass;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  fMyClass.Free;  // if refcount = 0 this works, if refcount <> 0 pointer error.
  //or
  fMyClass := Nil; // no error but Destroy wil not be executed
  Close();
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  fMyClass := TMyClass.Create();
end;
end.

阅读this article,只有构造函数没有实现析构函数。

这有什么特别的原因吗?

我是否应该通过实施 finalization 部分释放(如果需要)将在 myClass 中定义的所有其他对象?

析构函数未被调用的最可能原因是您没有将对象分配给接口变量。

procedure Test1;
var
  vMyObj : TObject;
begin
  vMyObj := myclass.Create;
end; <-Destructor NOT called here

procedure Test2;
var
  vMyIntf : IInterface;
begin
  vMyIntf := myclass.Create;
end; <-Destructor IS called here.

如果是这样,我邀请您阅读this answer了解更多信息。

你的fMyClass变量是对象引用,不是接口,所以它不参与TInterfaceObject的引用计数。

你需要改变这个:

fMyClass: TmyClass;

对此:

fMyClass: ITest;

然后你就可以完全摆脱 fMyClass.Free;:

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, 
  System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, 
  Vcl.Dialogs, Vcl.StdCtrls, unit2;

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

var
  Form1: TForm1;
  fMyClass: ITest;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
  fMyClass := nil; // no error and Destroy will be executed
  Close();
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  fMyClass := TMyClass.Create();
end;

end.

fMyClass := nil; 仅当 fMyClass 是接口变量而不是对象引用时才会调用引用计数,并且您不能在接口变量上调用 Free()