Question

我将创建的对象传递给另一个对象的构造函数，该对象需要该对象实现的接口。

  ISomeInterface = interface
  ['{840D46BA-B9FB-4273-BF56-AD0BE40AA3F9}']
  end;

  TSomeObject = class(TInterfacedObject, ISomeinterface)
  end;

  TSomeObject2 = class
  private
    FSomeInterface: ISomeinterface;
  public
    constructor Create(SomeObject: ISomeInterface);
  end;

var
Form1: TForm1; // main form
SomeObject: TSomeObject;

constructor TSomeObject2.Create(SomeObject: ISomeInterface);
begin
  FSomeInterface := SomeObject;
end;

// main form creating
procedure TForm1.FormCreate(Sender: TObject);
var SomeObject2: TSomeObject2;
begin
  SomeObject := TSomeObject.Create;
  //  SomeObject2 := TSomeObject2.Create(nil);        // ok
  SomeObject2 := TSomeObject2.Create(SomeObject);     // not ok
  try
  // do some things
  finally
    SomeObject2.Free;
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  SomeObject.Free; // if passed to a SomeObject2 Constructor - freeing it causing av
end;

关闭主窗体后，它会给我一个AV和内存泄漏 - 整个主窗体已泄露。如果我将nil传递给TSomeObject构造函数，一切都很顺利。编译器是否通过引用计数释放FSomeInterface并且我不应该尝试在mainForm SomeObject中释放destructor？我怎么能避免它？

Answer 1

TSomeObject继承自TInterfacedObject，因此被引用计数。您的TSomeObject实例未被引用计数，应该被接口变量删除或替换。

如果需要在FormCreate中创建的TSomeObject实例，则应将其分配给ISomeInterface类型的变量，以便引用计数也适用于此。

另一种方法是继承TInterfacedPersistant而不是TInterfacedObject以避免引用计数。

解释代码中发生的事情：

procedure TForm1.FormCreate(Sender: TObject);
var SomeObject2: TSomeObject2;
begin
  { Here you create the instance and assign it to a variable holding the instance.
    After this line the reference count of the instance is 0 }
  SomeObject := TSomeObject.Create;
  //  SomeObject2 := TSomeObject2.Create(nil);        // ok
  { Using the instance as a parameter will increase the reference count to 1 }
  SomeObject2 := TSomeObject2.Create(SomeObject);     // not ok
  try
  // do some things
  finally
    { Freeing SomeObject2 also destroys the interface reference FSomeInterface is
      pointing to (which is SomeObject), decreasing the reference count to 0, which
      in turn frees the instance of TSomeObject. }
    SomeObject2.Free;
  end;
  { Now, after SomeObject is freed, the variable points to invalid memory causing the
    AV in FormDestroy. }
end;

将对象引用作为接口传递

1 个答案: