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

#import <Foundation/Foundation.h>



@interface Cattle : NSObject {

	int legsCount;

}

- (void)saySomething;

- (void)setLegsCount:(int) count;

@end

Cattle.m

#import "Cattle.h"



@implementation Cattle



-(void) saySomething

{

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

}



-(void) setLegsCount:(int) count

{

	legsCount = count;

}

@end

子类“公牛" Bull.h

#import <Foundation/Foundation.h>

#import "Cattle.h"



@interface Bull : Cattle {

	NSString *skinColor;

}

- (void)saySomething;

- (NSString*) getSkinColor;

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

@end

Bull.m

#import "Bull.h"





@implementation Bull



-(void) saySomething

{

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

}



-(NSString*) getSkinColor

{

	return skinColor;

}



- (void) setSkinColor:(NSString *) color

{

	skinColor = color;

}

@end

代理类DoProxy.h (关键的代码都在这里)

#import <Foundation/Foundation.h>



//定义几个字符串常量

#define	SET_SKIN_COLOR @"setSkinColor:"

#define	BULL_CLASS @"Bull"

#define	CATTLE_CLASS @"Cattle"





@interface DoProxy : NSObject {

	BOOL notFirstRun;

	

	id cattle[3];

	//定义二个选择器

	SEL say;

	SEL skin;

	

	//定义一个函数指针(传统C语言的处理方式)

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

	

	//定义一个IMP方式的函数指针(obj-C中推荐的方式)

	IMP say_Func;

	

	//定义一个类

	Class bullClass;

}



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

-(void) setAllIVars;

-(void) SELFuncs;

-(void) functionPointers;



@end

DoProxy.m

#import "DoProxy.h"

#import "Cattle.h"

#import "Bull.h"



@implementation DoProxy





//初始化所有变量

- (void) setAllIVars

{	

	cattle[0] = [Cattle new];

	

	bullClass = NSClassFromString(BULL_CLASS);

	//即cattle[1],cattle[2]都是Bull类的实例

	cattle[1] = [bullClass new];

	cattle[2] = [bullClass new];

	

	say = @selector(saySomething);

	skin = NSSelectorFromString(SET_SKIN_COLOR);

}





//初始化id

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

{

	//第一次运行的时候

	if(notFirstRun == NO)

	{

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

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

		notFirstRun = YES;//修改初次运行标志位

	}

	

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

	

	//如果aCattle是Bull或Cattle类的实例

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

	{

		[aCattle setLegsCount:4];//设置牛的4条腿

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

		{

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

		}

		else

		{

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

		}

		[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)

	}

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

	{

		NSString *yourClassName = [aCattle className];

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

	}

}



//初始化选择器以及相应函数

- (void) SELFuncs

{

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

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

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

	[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

}



//函数指针测试

- (void) functionPointers

{

	//取得函数指针的第一种方式

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

	//上面的语句其实等效于下面这种方法

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

	

	//用第二种方法取得saySomething的函数指针

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

	

	//用函数指针的形式调用setSkinColor

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

	

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

	

	//调用saySomething方法

	say_Func(cattle[1],say); 

}



@end

测试主函数main()

#import <Foundation/Foundation.h>

#import "DoProxy.h"



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

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

	DoProxy *doProxy = [DoProxy new];

	

	[doProxy setAllIVars];

	[doProxy SELFuncs];

	[doProxy functionPointers];

	

	[doProxy release];

	[pool drain];

	return 0;

}

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.

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。