Delphi中的“委托”

.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。

[delphi]view plaincopy

1. {type
2. TMyDelegateFunc = function (AIntParam: integer; AStringParam: string): Boolean;
3. TMyDelegateProc = procedure (AIntParam: integer; AStringParam: string);
4. 　　//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：
5. type
6. TMyObjectDelegate = procedure (AIntParam: integer; AStringParam: string) of object; //对象的函数/过程
7. TMyRegularDelegate = procedure (AIntParam: integer; AStringParam: string); //非对象的（一般的）函数/过程
8. 　　//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。 }
9. 　　
10. unit UnitFrmTest;
11. interface
12. uses
13. Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
14. Dialogs, StdCtrls;
15. type
16. TDelegateType = (dtObject, dtRegular);
17. //对象的函数委托
18. TObjectNumFuncs = function (const ANumOne: Double;
19. const ANumTwo: Double): Double of object;
20. //非对象（一般）的函数委托
21. TRegularNumFuncs = function (const ANumOne: Double;
22. const ANumTwo: Double): Double;
23. type
24. TfrmTest = class(TForm)
25. edtNumOne: TEdit;
26. edtNumTwo: TEdit;
27. btnAdd: TButton;
28. btnSub: TButton;
29. btnMultiply: TButton;
30. btnDivide: TButton;
31. lblResult: TLabel;
32. rbObjectDelegate: TRadioButton;
33. rbRegularDelegate: TRadioButton;
34. procedure rbRegularDelegateClick(Sender: TObject);
35. procedure rbObjectDelegateClick(Sender: TObject);
36. procedure MyButtonClick(Sender: TObject);
37. private
38. { Private declarations }
39. //指示当前是使用对象的函数，还是非对象的函数
40. FDelegateType: TDelegateType;
41. { 对象的函数列表 }
42. function Add(const ANumOne: Double;
43. const ANumTwo: Double): Double;
44. function Sub(const ANumOne: Double;
45. const ANumTwo: Double): Double;
46. function Multiply(const ANumOne: Double;
47. const ANumTwo: Double): Double;
48. function Divide(const ANumOne: Double;
49. const ANumTwo: Double): Double;
50. { 对象的函数列表　结束 }
51. function DoObjectCalc(const ANumOne: Double;
52. const ANumTwo: Double; AMethod: TObjectNumFuncs): Double;
53. public
54. { Public declarations }
55. end;
56. { 非对象（一般）的函数列表 }
57. function Add(const ANumOne: Double; const ANumTwo: Double): Double;
58. function Sub(const ANumOne: Double; const ANumTwo: Double): Double;
59. function Multiply(const ANumOne: Double; const ANumTwo: Double): Double;
60. function Divide(const ANumOne: Double; const ANumTwo: Double): Double;
61. function DoRegularCalc(const ANumOne: Double; const ANumTwo: Double;
62. AMethod: TRegularNumFuncs): Double;
63. { 非对象（一般）的函数列表　结束 }
64. var
65. frmTest: TfrmTest;
66. implementation
67. {$R *.dfm}
68. { 非对象（一般）的函数列表 }
69. function Add(const ANumOne: Double; const ANumTwo: Double): Double;
70. begin
71. Result := ANumOne + ANumTwo;
72. end;
73. function Sub(const ANumOne: Double; const ANumTwo: Double): Double;
74. begin
75. Result := ANumOne - ANumTwo;
76. end;
77. function Multiply(const ANumOne: Double; const ANumTwo: Double): Double;
78. begin
79. Result := ANumOne * ANumTwo;
80. end;
81. function Divide(const ANumOne: Double; const ANumTwo: Double): Double;
82. begin
83. try
84. Result := ANumOne / ANumTwo;
85. except
86. on E: EZeroDivide do
87. begin
88. frmTest.edtNumTwo.SetFocus();
89. frmTest.lblResult.Caption := '除数不能为零';
90. Abort();
91. end;
92. end;
93. end;
94. function DoRegularCalc(const ANumOne: Double; const ANumTwo: Double;
95. AMethod: TRegularNumFuncs): Double;
96. begin
97. Result := AMethod(ANumOne, ANumTwo);
98. end;
99. { 非对象（一般）的函数列表　结束 }
100. { TfrmTest }
101. { 对象的函数列表 }
102. function TfrmTest.Add(const ANumOne, ANumTwo: Double): Double;
103. begin
104. Result := ANumOne + ANumTwo;
105. end;
106. function TfrmTest.Divide(const ANumOne, ANumTwo: Double): Double;
107. begin
108. try
109. Result := ANumOne / ANumTwo;
110. except
111. on E: EZeroDivide do
112. begin
113. edtNumTwo.SetFocus();
114. lblResult.Caption := '除数不能为零';
115. Abort;
116. end;
117. end;
118. end;
119. function TfrmTest.DoObjectCalc(const ANumOne, ANumTwo: Double;
120. AMethod: TObjectNumFuncs): Double;
121. begin
122. Result := AMethod(ANumOne, ANumTwo);
123. end;
124. function TfrmTest.Multiply(const ANumOne, ANumTwo: Double): Double;
125. begin
126. Result := ANumOne * ANumTwo;
127. end;
128. procedure TfrmTest.MyButtonClick(Sender: TObject);
129. var
130. dblNumOne, dblNumTwo, dblResult: Double;
131. begin
132. if not (Sender is TButton) then Exit;
133. dblNumOne := StrToFloatDef(Trim(edtNumOne.Text), 0.0);
134. dblNumTwo := StrToFloatDef(Trim(edtNumTwo.Text), 0.0);
135. case (Sender as TButton).Tag of
136. 0: //加
137. begin
138. case Self.FDelegateType of
139. dtObject:
140. begin
141. dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Add);
142. //若为
143. //dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, UnitFrmTest.Add);
144. //则会提示以下错误：
145. //E2009 Incompatible types: 'regular procedure and method pointer'
146. end;
147. dtRegular:
148. begin
149. dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Add);
150. //若为
151. //dblResult := DoRegularCalc(dblNumOne, dblNumTwo, Self.Add);
152. //则会提示以下错误：
153. //E2009 Incompatible types: 'regular procedure and method pointer'
154. end;
155. end;
156. end;
157. 1: //减
158. begin
159. case Self.FDelegateType of
160. dtObject:
161. begin
162. dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Sub);
163. end;
164. dtRegular:
165. begin
166. dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Sub);
167. end;
168. end;
169. end;
170. 2: //乘
171. begin
172. case Self.FDelegateType of
173. dtObject:
174. begin
175. dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Multiply);
176. end;
177. dtRegular:
178. begin
179. dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Multiply);
180. end;
181. end;
182. end;
183. 3: //除
184. begin
185. case Self.FDelegateType of
186. dtObject:
187. begin
188. dblResult := Self.DoObjectCalc(dblNumOne, dblNumTwo, Self.Divide);
189. end;
190. dtRegular:
191. begin
192. dblResult := DoRegularCalc(dblNumOne, dblNumTwo, UnitFrmTest.Divide);
193. end;
194. end;
195. end;
196. end;
197. lblResult.Caption := '结果：' + FloatToStr(dblResult);
198. end;
199. procedure TfrmTest.rbObjectDelegateClick(Sender: TObject);
200. begin
201. Self.FDelegateType := dtObject;
202. end;
203. procedure TfrmTest.rbRegularDelegateClick(Sender: TObject);
204. begin
205. Self.FDelegateType := dtRegular;
206. end;
207. function TfrmTest.Sub(const ANumOne, ANumTwo: Double): Double;
208. begin
209. Result := ANumOne - ANumTwo;
210. end;
211. { 对象的函数列表　结束 }
212. end.

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