ObjC(ObjectiveC)中的Class(类类型),Selector(选择器SEL),函数指针(IMP)

作者：菩提树下的杨过
出处：http://www.cnblogs.com/yjmyzz/archive/2011/02/28/1967451.html
本文版权归作者和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。

ObjC(Objective-C)中的Class(类类型),Selector(选择器SEL),函数指针(IMP)

今天在园子里看到了一篇牛文“Objective-C 2.0 with Cocoa Foundation--- 5，Class类型，选择器Selector以及函数指针 ”，讲得十分精彩，忍不住把它的代码加上注释整理于此，以便日后查看。

个人体会：obj-C中的“Class类型变量”比c#中的Object基类还要灵活，可以用它生成任何类型的实例（但是它又不是 NSObject）。而选择器SEL与函数指针IMP，如果非要跟c#扯上关系的话，这二个结合起来，就点类似c#中的反射+委托，可以根据一个方法名称 字符串，直接调用方法。

"牛"的基类 Cattle.h

1	#import <Foundation/Foundation.h>

2

3	@interface Cattle : NSObject {

4	int legsCount;

5

}

6	- (void)saySomething;

7	- (void)setLegsCount:(int) count;

8

@end

Cattle.m

01	#import "Cattle.h"

02

03	@implementation Cattle

04

05	-(void) saySomething

06

{

07	NSLog(@"Hello, I am a cattle, I have %d legs.", legsCount);

08

}

09

10	-(void) setLegsCount:(int) count

11

{

12	legsCount = count;

13

}

14

@end

子类“公牛" Bull.h

01	#import <Foundation/Foundation.h>

02	#import "Cattle.h"

03

04	@interface Bull : Cattle {

05	NSString *skinColor;

06

}

07	- (void)saySomething;

08	- (NSString*) getSkinColor;

09	- (void) setSkinColor:(NSString *) color;

10

@end

Bull.m

01	#import "Bull.h"

02

03

04	@implementation Bull

05

06	-(void) saySomething

07

{

08	NSLog(@"Hello, I am a %@ bull, I have %d legs.", [self getSkinColor],legsCount);

09

}

10

11	-(NSString*) getSkinColor

12

{

13	return skinColor;

14

}

15

16	- (void) setSkinColor:(NSString *) color

17

{

18	skinColor = color;

19

}

20

@end

代理类DoProxy.h (关键的代码都在这里)

01	#import <Foundation/Foundation.h>

02

03	//定义几个字符串常量

04	#define SET_SKIN_COLOR @"setSkinColor:"

05	#define BULL_CLASS @"Bull"

06	#define CATTLE_CLASS @"Cattle"

07

08

09	@interface DoProxy : NSObject {

10	BOOL notFirstRun;

11

12	id cattle[3];

13

//定义二个选择器

14

SEL say;

15

SEL skin;

16

17	//定义一个函数指针(传统C语言的处理方式)

18	void(*setSkinColor_Func)(id,SEL,NSString*);

19

20	//定义一个IMP方式的函数指针(obj-C中推荐的方式)

21	IMP say_Func;

22

23

//定义一个类

24	Class bullClass;

25

}

26

27	-(void) doWithCattleId:(id) aCattle colorParam:(NSString*) color;

28	-(void) setAllIVars;

29	-(void) SELFuncs;

30	-(void) functionPointers;

31

32

@end

DoProxy.m

01	#import "DoProxy.h"

02	#import "Cattle.h"

03	#import "Bull.h"

04

05	@implementation DoProxy

06

07

08

//初始化所有变量

09	- (void) setAllIVars

10

{

11	cattle[0] = [Cattle new];

12

13	bullClass = NSClassFromString(BULL_CLASS);

14	//即cattle[1],cattle[2]都是Bull类的实例

15	cattle[1] = [bullClass new];

16	cattle[2] = [bullClass new];

17

18	say = @selector(saySomething);

19	skin = NSSelectorFromString(SET_SKIN_COLOR);

20

}

21

22

23

//初始化id

24	- (void) doWithCattleId:(id) aCattle colorParam:(NSString*) color

25

{

26	//第一次运行的时候

27	if(notFirstRun == NO)

28

{

29	NSString *myName = NSStringFromSelector(_cmd);//取得当前正在执行的方法的名字

30	NSLog(@"Running in the method of %@", myName);

31	notFirstRun = YES;//修改初次运行标志位

32

}

33

34	NSString *cattleParamClassName = [aCattle className];//取得aCattle的"类名称"

35

36	//如果aCattle是Bull或Cattle类的实例

37	if([cattleParamClassName isEqualToString:BULL_CLASS] || [cattleParamClassName isEqualToString:CATTLE_CLASS])

38

{

39	[aCattle setLegsCount:4];//设置牛的4条腿

40	if([aCattle respondsToSelector:skin])//如果aCattle对应的是类中,有定义方法"setSkinColor"

41

{

42	[aCattle performSelector:skin withObject:color];//则调用setSkinColor方法

43

}

44

else

45

{

46	NSLog(@"Hi, I am a %@, have not setSkinColor!", cattleParamClassName);//否则输出相应的提示信息

47

}

48	[aCattle performSelector:say];//最后执行saySomething方法(这二个方法在Bull与Cattle类中都有,所以肯定能运行)

49

}

50	else //如果aCattle即不是Bull类也不是Cattle类的实例

51

{

52	NSString *yourClassName = [aCattle className];

53	NSLog(@"Hi, you are a %@, but I like cattle or bull!", yourClassName);//显示这个"异类"的相关信息

54

}

55

}

56

57	//初始化选择器以及相应函数

58	- (void) SELFuncs

59

{

60	[self doWithCattleId:cattle[0] colorParam:@"brown"];

61	[self doWithCattleId:cattle[1] colorParam:@"red"];

62	[self doWithCattleId:cattle[2] colorParam:@"black"];

63	[self doWithCattleId:self colorParam:@"haha"];//这里故意传入一个异类self(即DoProxy本身),DoProxy当然不是Bull或Cattle

64

}

65

66

//函数指针测试

67	- (void) functionPointers

68

{

69	//取得函数指针的第一种方式

70	setSkinColor_Func=(void (*)(id, SEL, NSString*)) [cattle[1] methodForSelector:skin];

71	//上面的语句其实等效于下面这种方法

72	//IMP setSkinColor_Func = [cattle[1] methodForSelector:skin];

73

74	//用第二种方法取得saySomething的函数指针

75	say_Func = [cattle[1] methodForSelector:say];

76

77	//用函数指针的形式调用setSkinColor

78	setSkinColor_Func(cattle[1],skin,@"verbose");

79

80	NSLog(@"Running as a function pointer will be more efficiency!");

81

82	//调用saySomething方法

83	say_Func(cattle[1],say);

84

}

85

86

@end

测试主函数main()

01	#import <Foundation/Foundation.h>

02	#import "DoProxy.h"

03

04	int main (int argc, const char * argv[]) {

05	NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

06	DoProxy *doProxy = [DoProxy new];

07

08	[doProxy setAllIVars];

09	[doProxy SELFuncs];

10	[doProxy functionPointers];

11

12	[doProxy release];

13	[pool drain];

14

return 0;

15

}

运行结果：

2011-02-28 21:40:33.240 HelloSelector[630:a0f] Running in the method of doWithCattleId:colorParam:
2011-02-28 21:40:33.245 HelloSelector[630:a0f] Hi, I am a Cattle, have not setSkinColor!
2011-02-28 21:40:33.247 HelloSelector[630:a0f] Hello, I am a cattle, I have 4 legs.
2011-02-28 21:40:33.248 HelloSelector[630:a0f] Hello, I am a red bull, I have 4 legs.
2011-02-28 21:40:33.250 HelloSelector[630:a0f] Hello, I am a black bull, I have 4 legs.
2011-02-28 21:40:33.251 HelloSelector[630:a0f] Hi, you are a DoProxy, but I like cattle or bull!
2011-02-28 21:40:33.252 HelloSelector[630:a0f] Running as a function pointer will be more efficiency!
2011-02-28 21:40:33.254 HelloSelector[630:a0f] Hello, I am a verbose bull, I have 4 legs.