Delphi XE10.1 引用计数

 

以往的Delphi版本,不支持接口的Weak,和UnSafe的引用,支持对象的Weak, UnSafe,而且仅在Android和Ios平台上支持。

现在Delphi XE10.1 Berlin终于增加了对接口的Weak, UnSafe的支持。

 

1.Weak

Weak引用,不影响引用计数器,但是如果对象被释放,Weak引用变量自动清0,来看例子:

type
  TA=class(TInterfacedObject)

  end;

procedure TForm1.Button1Click(Sender: TObject);
var
  a:IInterface;
  [weak]aweak:IInterface;
begin
  a:=TA.Create;   //创建对象,复制给a,执行完成后引用计数器=1
  aweak:=a;       //由于aweak定义有[weak]属性,所以赋值给aweak后,引用计数器依旧为1,但aweak变量的地址被保存到一个weak关联列表中
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aweak))]));
  a:=nil;         //由于引用计数器=1,执行此句后,计数器清0,对象被释放,同时与此对weak关联列表中所有变量也被赋值为nil,包括aweak变量.
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aweak))]));
end;

  

运行结果

Ptr:16360080
Ptr:0

weak引用非常适合用于两个对象需要互相引用的情况下,如果以往的引用,将无法让引用计数器清0.

如下面的例子,互相引用后,两个对象的计数器都不清0,导致内存泄漏

type 
ISimpleInterface = interface 
  procedure DoSomething; 
  procedure AddObjectRef (simple: ISimpleInterface); 
end; 

TObjectOne = class (TInterfacedObject, ISimpleInterface) 
private 
  anotherObj: ISimpleInterface; 
public 
  procedure DoSomething; 
  procedure AddObjectRef (simple: ISimpleInterface); 
end;

.....................

procedure TObjectOne.AddObjectRef (simple: ISimpleInterface); 
begin
  anotherObj:=simple;
end;

.....................

var 
  one, two: ISimpleInterface; 
begin 
  one := TObjectOne.Create; 
  two := TObjectOne.Create; 
  one.AddObjectRef (two); 
  two.AddObjectRef (one);

这时候在Delphi XE10.1 Berlin下可以用weak引用,来快速方便的解决泄漏问题:

private 
  [weak] anotherObj: ISimpleInterface;

  

2.UnSafe

 

unsafe引用,不影响引用计数,但不会向Weak引用那样清零引用的变量。

type
  TA=class(TInterfacedObject)

  end;
procedure TForm1.Button2Click(Sender: TObject);
var
  a:IInterface;
  [unsafe]aunsafe:IInterface;
begin
  a:=TA.Create;
  aunsafe:=a;
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aunsafe))]));
  a:=nil;
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aunsafe))]));
end;

  

运行结果

Ptr:42640064
Ptr:42640064

 

由于Unsafe引用,不影响应用计数器,下面的程序将导致内存泄漏:

procedure TForm1.Button2Click(Sender: TObject); 
var 
  [unsafe] one: ISomeInterface;
begin 
  one := TSomeObject.Create; 
  one.DoSomething;
end;

  

 

posted @ 2016-05-28 12:12 子航 阅读(...) 评论(...) 编辑 收藏