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
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