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!