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.