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Delphi学习:OOP 中的双刃剑

来源:互联网网民  宽屏版  评论
2006-12-16 17:27:43

本文为【Delphi学习:OOP 中的双刃剑】的汉字拼音对照版显示拼音

qianjitiankanyifenfeichangyoumingdeshangyekongjiandeyuanmafaxianyigefeichangyouqudeyongfa

Integer(xxx) := aaa;

Tttt(xxx) := bbb;

xixipinweifaxianliyongzhezhongyongfawangwangkeyishoudaoyixiangbudaodexiaoguo

biru

TTestRec = record

A, B, C: Integer;

end;

TTestCls = class

private

FInner: TTestRec;

FReadOnlyValue: Integer;

function GetNewInner: PTestRec;

public

property Inner: TTestRec read FInner write FInner;

property NewInner: PTestRec read GetNewInner;

property ReadOnlyValue: Integer read FReadOnlyValue;

end;

nihuifaxianzhijiedenishigaibule aTestCls.Inner.A debianyishi delphi zhijiebaocuoyinwei delphi 7 zhongliangge recode fuzhishi copy memory erbushijiandandechuanzhi

procedure TForm1.Button1Click(Sender: TObject);

begin

with TTestCls.Create do

try

// Inner.A := 10;

Caption := TButton(Sender).Caption + ' A := ' + IntToStr(Inner.A);

finally

Free;

end;

end;

keshiruguowomenzhidaozai访fangwenzhege Inner shi delphi zaibianyizhijie FInner dedizhinamejieheshangmiannazhongyouqudeyongfa

procedure TForm1.Button3Click(Sender: TObject);

var

p: PInteger;

begin

with TTestCls.Create do

try

p := @(Inner.A);

Integer(p^) := 100;

Caption := TButton(Sender).Caption + ' A := ' + IntToStr(Inner.A);

finally

Free;

end;

end;

gengjinyibuliyongzhizhenjingrankeyitupo oo dui private debaohu

procedure TForm1.Button4Click(Sender: TObject);

var

p: PInteger;

begin

with TTestCls.Create do

try

p := @(ReadOnlyValue);

Integer(p^) := 1000;

Caption := TButton(Sender).Caption + ' ReadOnlyValue := ' + IntToStr(ReadOnlyValue);

||||||

finally

Free;

end;

end;

zhiyucaiguojienagengbuzaihuaxia

procedure TForm1.Button5Click(Sender: TObject);

var

p1, p2: PInteger;

begin

with TTestCls.Create do

try

p1 := @(Inner.A);

// neicunzhong FInner yu FReadOnlyValue qishizhicha TTestRec daxiaogezijie

Integer(p2) := Integer(p1) + SizeOf(TTestRec);

Integer(p2^) := 100;

Caption := TButton(Sender).Caption + ' ReadOnlyValue := ' + IntToStr(ReadOnlyValue);

finally

Free;

end;

end;

dangranzhizhenbudankeyipohuai ooyeneng使shinindedaimagengjiade oo

TTestRec = record

A, B, C: Integer;

end;

PTestRec = ^TTestRec;

TTestCls = class

private

FInner: TTestRec;

FReadOnlyValue: Integer;

function GetNewInner: PTestRec;

public

property Inner: TTestRec read FInner write FInner;

property NewInner: PTestRec read GetNewInner;

property ReadOnlyValue: Integer read FReadOnlyValue;

end;

procedure TForm1.Button2Click(Sender: TObject);

begin

with TTestCls.Create do

try

NewInner.A := 10;

Caption := TButton(Sender).Caption + ' A := ' + IntToStr(Inner.A);

finally

Free;

end;

end;

kankanxianshizhongdefei oo dedaima

liyongzhizhenfanganba Txxx gaicheng Pxxx houjingranduiyuanlaidedaimayidianyingxiangdoumeiyouer使shizhigengjiade oo

原文
 
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 前几天看一份非常有名的商业控件的源码,发现一个非常有趣的用法:   Integer(xxx) := aaa;   Tttt(xxx) := bbb;   细细品味,发现利用这种用法往往可以收到意想不到的效果:   比如: TTestRec = record A, B, C: Integer; end; TTestCls = class private FInner: TTestRec; FReadOnlyValue: Integer; function GetNewInner: PTestRec; public property Inner: TTestRec read FInner write FInner; property NewInner: PTestRec read GetNewInner; property ReadOnlyValue: Integer read FReadOnlyValue; end;   你会发现,直接的你是改不了 aTestCls.Inner.A 的(编译时 delphi 直接报错,因为 delphi 7 中两个 recode 赋值是 copy memory 而不是简单的“传址”! procedure TForm1.Button1Click(Sender: TObject); begin with TTestCls.Create do try // Inner.A := 10; Caption := TButton(Sender).Caption + ' A := ' + IntToStr(Inner.A); finally Free; end; end;   可是,如果我们知道在访问这个 Inner 时 delphi 在编译直接 FInner 的地址,那么,结合上面那种有趣的用法: procedure TForm1.Button3Click(Sender: TObject); var p: PInteger; begin with TTestCls.Create do try p := @(Inner.A); Integer(p^) := 100; Caption := TButton(Sender).Caption + ' A := ' + IntToStr(Inner.A); finally Free; end; end;   更进一步,利用指针竟然可以突破 oo 对 private 的保护: procedure TForm1.Button4Click(Sender: TObject); var p: PInteger; begin with TTestCls.Create do try p := @(ReadOnlyValue); Integer(p^) := 1000; Caption := TButton(Sender).Caption + ' ReadOnlyValue := ' + IntToStr(ReadOnlyValue); |||||| finally Free; end; end;   至于“踩过界”那更不在话下: procedure TForm1.Button5Click(Sender: TObject); var p1, p2: PInteger; begin with TTestCls.Create do try p1 := @(Inner.A); // 内存中 FInner 与 FReadOnlyValue 其实只差 TTestRec 大小个字节 Integer(p2) := Integer(p1) + SizeOf(TTestRec); Integer(p2^) := 100; Caption := TButton(Sender).Caption + ' ReadOnlyValue := ' + IntToStr(ReadOnlyValue); finally Free; end; end;   当然,指针不但可以破坏 oo,也能使您的代码更加的 oo: TTestRec = record A, B, C: Integer; end; PTestRec = ^TTestRec; TTestCls = class private FInner: TTestRec; FReadOnlyValue: Integer; function GetNewInner: PTestRec; public property Inner: TTestRec read FInner write FInner; property NewInner: PTestRec read GetNewInner; property ReadOnlyValue: Integer read FReadOnlyValue; end; procedure TForm1.Button2Click(Sender: TObject); begin with TTestCls.Create do try NewInner.A := 10; Caption := TButton(Sender).Caption + ' A := ' + IntToStr(Inner.A); finally Free; end; end;   看看现实中的非 oo 的代码:   利用“指针方案”把 Txxx 改成 Pxxx 后竟然对原来的代码一点影响都没有,而使之更加的 oo
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