关于 class helper for ... 语法

转载于万一的博客https://www.cnblogs.com/del/archive/2009/10/13/1582789.html

 

class helper 可能是从 Delphi 2007 增加的新语法, 因为感觉不太实用, 直到今天才测试了一下.
试过之后才知道: 挺有意思的! 基本功能就是修改已存在的类.

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Txxx = class helper for T... {T... 表示已存在的类}   {可以替换已存在的方法}   {也可以有新的方法、成员} end;   //这之后再使用 T... 类及其子孙类时, 都会优先使用 Txxx 的修改

例一:

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unit Unit1;   interface   uses   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,   Dialogs, StdCtrls;   type   TForm1 = class(TForm)     Button1: TButton;     procedure Button1Click(Sender: TObject);   end;     TMyClass = class     function func1: string;     function func2: string;   end;     TMyClassHelper = class helper for TMyClass     function func1: string; {将把 TMyClass 的同名方法替换掉}     function func3: string; {将为 TMyClass 及其子类增加这个方法}   end;   var   Form1: TForm1;   implementation   {$R *.dfm}   { TMyClass }   function TMyClass.func1: string; begin   Result := 'TMyClass.func1'; end;   function TMyClass.func2: string; begin   Result := 'TMyClass.func2'; end;   { TMyClassHelper }   function TMyClassHelper.func1: string; begin   Result := 'TMyClassHelper.func1'; end;   function TMyClassHelper.func3: string; begin   Result := 'TMyClassHelper.func3'; end;   //测试 procedure TForm1.Button1Click(Sender: TObject); var   obj: TMyClass; begin   obj := TMyClass.Create;     ShowMessage(obj.func1); {TMyClassHelper.func1}   ShowMessage(obj.func2); {TMyClass.func2}   ShowMessage(obj.func3); {TMyClassHelper.func3}     obj.Free; end;   end.

例二: 本例为 TControl 类增加了一个方法, 之后 TControl 及其所有子孙类就都拥有了这个方法.

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unit Unit1;   interface   uses   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,   Dialogs, StdCtrls;   type   TForm1 = class(TForm)     Button1: TButton;     procedure Button1Click(Sender: TObject);   end;     TMyClassHelper = class helper for TControl     procedure MyMsg;   end;   var   Form1: TForm1;   implementation   {$R *.dfm}   { TMyClassHelper }   procedure TMyClassHelper.MyMsg; begin   ShowMessageFmt('%s 的类名是 %s', [Name,ClassName]); end;   //测试: 这里测试了当前窗体和当前按钮, 它们都是从 TControl 继承来的 procedure TForm1.Button1Click(Sender: TObject); begin   Self.MyMsg;            {Form1 的类名是 TForm1}   TButton(Sender).MyMsg; {Button1 的类名是 TButton1} end;   end.

　菜根大神的方法

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type   TMyObject = class   private     FX : Integer;   public     property X: Integer read FX write FX;   end;   type   TMyObjectHelper = class helper for TMyObject   type     PMyObjHelperData = ^TMyObjHelperData;     TMyObjHelperData = record     public       FY: Integer;     end;   private     class constructor Create;   public     function GetData: PMyObjHelperData;     function GetXYValue : Integer;     procedure SetY(Y: Integer);   end;   class constructor TMyObjectHelper.Create; var   P: Pointer;   ASize: Integer;   T: NativeUInt; begin   P := PByte(TMyObject) + vmtInstanceSize;   ReadProcessMemory(GetCurrentProcess, P, @ASize, SizeOf(ASize), T);   Inc(ASize, SizeOf(TMyObjHelperData));   WriteProcessMemory(GetCurrentProcess, P, @ASize, SizeOf(ASize), T); end;   function TMyObjectHelper.GetData: PMyObjHelperData; begin   Result :=     Pointer(PByte(Self) + InstanceSize - hfFieldSize + hfMonitorOffset - SizeOf(TMyObjHelperData)); end;   function TMyObjectHelper.GetXYValue : Integer; var   AData: PMyObjHelperData; begin   AData := GetData;   Result:= FX + AData.FY; end;   procedure TMyObjectHelper.SetY(Y: Integer); var   AData: PMyObjHelperData; begin   AData := GetData;   AData.FY := Y; end;   procedure TForm1.Button5Click(Sender: TObject); var   AObj: TMyObject; begin   AObj := TMyObject.Create;   AObj.X := 200;   AObj.SetY(100);   ShowMessage(AObj.GetXYValue.ToString);   AObj.Free; end;