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objective-C中的Class(类类型),Selector

objective-C中的Class(类类型),Selector

作者: 有来有趣ly | 来源:发表于2016-02-25 09:31 被阅读0次

    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
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    import <Foundation/Foundation.h>

    @interface Cattle : NSObject {
    int legsCount;
    }

    • (void)saySomething;
    • (void)setLegsCount:(int) count;
      @end
      Cattle.m
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    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
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    import <Foundation/Foundation.h>

    import "Cattle.h"

    @interface Bull : Cattle {
    NSString *skinColor;
    }

    • (void)saySomething;
    • (NSString*) getSkinColor;
    • (void) setSkinColor:(NSString *) color;
      @end
      Bull.m
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    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)
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    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
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    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()
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    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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