红鱼儿

统计

说说Delphi 10.4的对象释放

随着Delphi 10.4去掉了ARC,统一移动平台与桌面平台的内存管理,那对于释放对象,有什么变化呢?

先看看10.4的代码:

procedure TObject.Free;
begin
// under ARC, this method isn't actually called since the compiler translates
// the call to be a mere nil assignment to the instance variable, which then calls _InstClear
{$IFNDEF AUTOREFCOUNT}
  if Self <> nil then
    Destroy;
{$ENDIF}
end;

procedure TObject.DisposeOf;
type
  TDestructorProc = procedure (Instance: Pointer; OuterMost: ShortInt);
begin
{$IFDEF AUTOREFCOUNT}
  if Self <> nil then
  begin
    Self.__ObjAddRef; // Ensure the instance remains alive throughout the disposal process
    try
      if __SetDisposed(Self) then
      begin
        _BeforeDestruction(Self, 1);
        TDestructorProc(PPointer(PByte(PPointer(Self)^) + vmtDestroy)^)(Self, 0);
      end;
    finally
      Self.__ObjRelease; // This will deallocate the instance if the above process cleared all other references.
    end;
  end;
{$ELSE}
  Free;
{$ENDIF}
end;

可以清楚的看到,在DisposeOf中,如果没有定义AUTOREFCOUNT编译变量,则直接调用Free方法。由于去掉ARC,AUTOREFCOUNT不再定义,所以调用DisposeOf,就是调用Free。现在可以忘记DisposeOf了,所有平台释放对象,就用Free。

接下来,再看看FreeAndNil方法:

procedure FreeAndNil(const [ref] Obj: TObject);
{$IF not Defined(AUTOREFCOUNT)}
var
  Temp: TObject;
begin
  Temp := Obj;
  TObject(Pointer(@Obj)^) := nil;
  Temp.Free;
end;
{$ELSE}
begin
  Obj := nil;
end;
{$ENDIF}

这个方法,同样使用了AUTOREFCOUNT编译变量。

为了验证移动平台下,是否定义了AUTOREFCOUNT,笔者做了个测试代码:

procedure TForm1.FormCreate(Sender: TObject);
begin
{$IFDEF AUTOREFCOUNT}
   Text1.Text:='AUTOREFCOUNT';
{$ELSE}
   Text1.Text:='Not Defined AUTOREFCOUNT';
{$ENDIF}
end;

事实证明,在android运行时,显示Not Defined AUTOREFCOUNT。没有定义AUTOREFCOUNT,你可按这个去读上面的代码了!

 

posted on 2020-06-17 13:10  红鱼儿  阅读(...)  评论(...编辑  收藏