预处理

1.文件包含

#import <Foundation/Foundation.h>

2.宏定义

#define JR_PI 3.14
#define JR_MAX(a,b) ((a>b)?(a):(b)) //得到两个数中较大值
#define JR_SQUARE_1(n) n*n  //求数字的平方
#define JR_SQUARE_2(n) (n)*(n) //求数字的平方
#define JR_HELLO @"hello world";

3.条件编译

#import <Foundation/Foundation.h>

#define JR_COUNT 10

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
#if defined(JR_COUNT)
        NSLog(@"定义了 COUNT 这个宏");
#endif
        
#if defined(JR_MAX)
        NSLog(@"没有定义了 JR_MAX 这个宏");
#endif
        
#if JR_COUNT==1
        NSLog(@"JR_COUNT=1");
#elif JR_COUNT==2
        NSLog(@"JR_COUNT=2");
#elif JR_COUNT==3
        NSLog(@"JR_COUNT=3");
#else 
        NSLog(@"JR_COUNT=%i",JR_COUNT);
#endif
        
    }
    return 0;
}

SEL

一个关键字，就像int，long一样，它声明了一种类型：类方法指针。

#import "ViewController.h"
 
@interface ViewController ()
{
     SEL myLog;
}
@end

传递方式：

@interface ViewController ()
{
     SEL myLog;
}
@end
 
@implementation ViewController
 

- ( void )viewDidLoad {
   [super viewDidLoad];

   #第一种
   myLog = @selector(myLogL);
   //通过performSelector来执行方法
   #第二种
   myLog = NSSelectorFromString(@ "myLogN" );
   [self performSelector:myLog]; //打印 “myLog”

}

-( void )myLogL{
     NSLog(@ "myLog" );
}

例子

//Mybutton.h中
#import <UIKit/UIKit.h>
@interface Mybutton : UIButton
-( void )addMyTarget:(id)target action:(SEL)action;
@end


//Mybutton.m中
#import "Mybutton.h"
@implementation Mybutton
{
     SEL _action;
     id _target;
}

-( void )addMyTarget:(id)target action:(SEL)action{
     _target=target;
     _action=action;
}

-( void )touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
     [_target performSelector:_action];
}
@end


//外部
- ( void )viewDidLoad {
     [super viewDidLoad];
     Mybutton * btn = [[Mybutton alloc]initWithFrame:CGRectMake(100, 100, 60, 60)];
     btn.backgroundColor=[UIColor redColor];
     [btn addMyTarget:self action:@selector(click)];
     [self.view addSubview:btn];
}
 
-( void )click{
     NSLog(@ "点击了btn" );
}