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  • objectiveC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://yjmyzz.cnblogs.com
    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。
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  • 原文地址:https://www.cnblogs.com/yjmyzz/p/1967451.html
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