标签:nil 需要 nsa dex format obj lines 属性 tab
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:
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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
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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
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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:
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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。
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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
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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:
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procedure TForm1 . Button2Click(Sender: TObject); var [unsafe] one: ISomeInterface; begin one := TSomeObject . Create; one . DoSomething; end ; |
https://www.cnblogs.com/hezihang/p/5536928.html#undefined
Delphi XE10.1 引用计数(Delphi XE10.1 Berlin终于增加了对接口的Weak, UnSafe的支持)
标签:nil 需要 nsa dex format obj lines 属性 tab
原文地址:https://www.cnblogs.com/findumars/p/11579222.html