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

╰半夏微凉° 2022-07-15 00:20 112阅读 0赞

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

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 
    
    @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 
    #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 
    
    //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 
    #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\[630:a0f\] Runningin 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 acattle, I have 4 legs.  
2011-02-28 21:40:33.248 HelloSelector\[630:a0f\] Hello, I am a redbull, I have 4 legs.  
2011-02-28 21:40:33.250 HelloSelector\[630:a0f\] Hello, I am a blackbull, I have 4 legs.  
2011-02-28 21:40:33.251 HelloSelector\[630:a0f\] Hi, you are aDoProxy, but I like cattle or bull!  
2011-02-28 21:40:33.252 HelloSelector\[630:a0f\] Running as afunction pointer will be more efficiency!  
2011-02-28 21:40:33.254 HelloSelector\[630:a0f\] Hello, I am averbose bull, I have 4 legs.