ObjC(Objective-C)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.