Delphi中的“委托”

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.NET中有委托（Delegate）的概念，其声明形式如下所示：

public delegate void MyDelegate(int aIntParam, string aStringParam);

　　依个人所见，委托实际上就是规定一种接口，提供一种规范，任何符合该委托签名的函数/过程都属于同一类。

　　在Delphi中，也有类似于“委托”的概念（不过可没有C#的功能丰富，不过两者从根本上说都应该是函数指针），如下所示：

type
TMyDelegateFunc = function (AIntParam: integer; AStringParam: string): Boolean;
TMyDelegateProc = procedure (AIntParam: integer; AStringParam: string);

　　在以上的声明中，还可以用of object关键字来规定所定义的“委托”是应用于对象的函数/过程，还是应用于非对象的函数/过程，例：

type
TMyObjectDelegate = procedure (AIntParam: integer; AStringParam: string) of object; //对象的

函数/过程
TMyRegularDelegate = procedure (AIntParam: integer; AStringParam: string); //非对象的（一般的）函数/过程

　　以下举个简单的例子来说明一下Delphi中“委托”的应用。附件为完整程序。
　　

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{type
TMyDelegateFunc = function (AIntParam: integer; AStringParam: string): Boolean;
TMyDelegateProc = procedure (AIntParam: integer; AStringParam: string);
　　//在以上的声明中，还可以用of object关键字来规定所定义的“委托”是应用于对象的函数/过程，还是应用于非对象的函数/过程，例：
type
TMyObjectDelegate = procedure (AIntParam: integer; AStringParam: string) of object; //对象的函数/过程
TMyRegularDelegate = procedure (AIntParam: integer; AStringParam: string); //非对象的（一般的）函数/过程
　　//以下举个简单的例子来说明一下Delphi中“委托”的应用。附件为完整程序。 }
　　
unit UnitFrmTest;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TDelegateType = (dtObject, dtRegular);
//对象的函数委托
TObjectNumFuncs = function (const ANumOne: Double;
const ANumTwo: Double): Double of object;
//非对象（一般）的函数委托
TRegularNumFuncs = function (const ANumOne: Double;
const ANumTwo: Double): Double;
type
TfrmTest = class(TForm)
edtNumOne: TEdit;
edtNumTwo: TEdit;
btnAdd: TButton;
btnSub: TButton;
btnMultiply: TButton;
btnDivide: TButton;
lblResult: TLabel;
rbObjectDelegate: TRadioButton;
rbRegularDelegate: TRadioButton;
procedure rbRegularDelegateClick(Sender: TObject);
procedure rbObjectDelegateClick(Sender: TObject);
procedure MyButtonClick(Sender: TObject);
private
{ Private declarations }
//指示当前是使用对象的函数，还是非对象的函数
FDelegateType: TDelegateType;
{ 对象的函数列表 }
function Add(const ANumOne: Double;
const ANumTwo: Double): Double;
function Sub(const ANumOne: Double;
const ANumTwo: Double): Double;
function Multiply(const ANumOne: Double;
const ANumTwo: Double): Double;
function Divide(const ANumOne: Double;
const ANumTwo: Double): Double;
{ 对象的函数列表　结束 }
function DoObjectCalc(const ANumOne: Double;
const ANumTwo: Double; AMethod: TObjectNumFuncs): Double;
public
{ Public declarations }
end;
{ 非对象（一般）的函数列表 }
function Add(const ANumOne: Double; const ANumTwo: Double): Double;
function Sub(const ANumOne: Double; const ANumTwo: Double): Double;
function Multiply(const ANumOne: Double; const ANumTwo: Double): Double;
function Divide(const ANumOne: Double; const ANumTwo: Double): Double;
function DoRegularCalc(const ANumOne: Double; const ANumTwo: Double;
AMethod: TRegularNumFuncs): Double;
{ 非对象（一般）的函数列表　结束 }
var
frmTest: TfrmTest;
implementation
{$R *.dfm}
{ 非对象（一般）的函数列表 }
function Add(const ANumOne: Double; const ANumTwo: Double): Double;
begin
Result := ANumOne + ANumTwo;
end;
function Sub(const ANumOne: Double; const ANumTwo: Double): Double;
begin
Result := ANumOne - ANumTwo;
end;
function Multiply(const ANumOne: Double; const ANumTwo: Double): Double;
begin
Result := ANumOne * ANumTwo;
end;
function Divide(const ANumOne: Double; const ANumTwo: Double): Double;
begin
try
Result := ANumOne / ANumTwo;
except
on E: EZeroDivide do
begin
frmTest.edtNumTwo.SetFocus();
frmTest.lblResult.Caption := '除数不能为零';
Abort();
end;
end;
end;
function DoRegularCalc(const ANumOne: Double; const ANumTwo: Double;
AMethod: TRegularNumFuncs): Double;
begin
Result := AMethod(ANumOne, ANumTwo);
end;
{ 非对象（一般）的函数列表　结束 }
{ TfrmTest }
{ 对象的函数列表 }
function TfrmTest.Add(const ANumOne, ANumTwo: Double): Double;
begin
Result := ANumOne + ANumTwo;
end;
function TfrmTest.Divide(const ANumOne, ANumTwo: Double): Double;
begin
try
Result := ANumOne / ANumTwo;
except
on E: EZeroDivide do
begin
edtNumTwo.SetFocus();
lblResult.Caption := '除数不能为零';
Abort;
end;
end;
end;
function TfrmTest.DoObjectCalc(const ANumOne, ANumTwo: Double;
AMethod: TObjectNumFuncs): Double;
begin
Result := AMethod(ANumOne, ANumTwo);
end;
function TfrmTest.Multiply(const ANumOne, ANumTwo: Double): Double;
begin
Result := ANumOne * ANumTwo;
end;
procedure TfrmTest.MyButtonClick(Sender: TObject);
var
dblNumOne, dblNumTwo, dblResult: Double;
begin
if not (Sender is TButton) then Exit;
dblNumOne := StrToFloatDef(Trim(edtNumOne.Text), 0.0);
dblNumTwo := StrToFloatDef(Trim(edtNumTwo.Text), 0.0);
case (Sender as TButton).Tag of
0: //加
begin
case Self.FDelegateType of
dtObject:
begin
dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Add);
//若为
//dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, UnitFrmTest.Add);
//则会提示以下错误：
//E2009 Incompatible types: 'regular procedure and method pointer'
end;
dtRegular:
begin
dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Add);
//若为
//dblResult := DoRegularCalc(dblNumOne, dblNumTwo, Self.Add);
//则会提示以下错误：
//E2009 Incompatible types: 'regular procedure and method pointer'
end;
end;
end;
1: //减
begin
case Self.FDelegateType of
dtObject:
begin
dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Sub);
end;
dtRegular:
begin
dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Sub);
end;
end;
end;
2: //乘
begin
case Self.FDelegateType of
dtObject:
begin
dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Multiply);
end;
dtRegular:
begin
dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Multiply);
end;
end;
end;
3: //除
begin
case Self.FDelegateType of
dtObject:
begin
dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Divide);
end;
dtRegular:
begin
dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Divide);
end;
end;
end;
end;
lblResult.Caption := '结果：' + FloatToStr(dblResult);
end;
procedure TfrmTest.rbObjectDelegateClick(Sender: TObject);
begin
Self.FDelegateType := dtObject;
end;
procedure TfrmTest.rbRegularDelegateClick(Sender: TObject);
begin
Self.FDelegateType := dtRegular;
end;
function TfrmTest.Sub(const ANumOne, ANumTwo: Double): Double;
begin
Result := ANumOne - ANumTwo;
end;
{ 对象的函数列表　结束 }
end.