現在開發基本上都有發送驗證碼，倒計時,下面說一種

#import <UIKit/UIKit.h>

@interface UIButton (CountDown)
-(void)startTime:(NSInteger )timeout title:(NSString *)tittle waitTittle:(NSString *)waitTittle;
@end

#import "UIButton+CountDown.h"

@implementation UIButton (CountDown)
-(void)startTime:(NSInteger )timeout title:(NSString *)tittle waitTittle:(NSString *)waitTittle{
    __block NSInteger timeOut
 
=timeout; //倒計時時間
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
    dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒執行
    dispatch_source_set_event_handler(_timer, ^{
        
 
if(timeOut<=0){ //倒計時結束，關閉
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                //設置界面的按鈕顯示 根據自己需求設置
                [self setTitle:tittle forState:UIControlStateNormal];
                self.userInteractionEnabled = YES;
            });
        }
 
else{
            //            int minutes = timeout / 60;
            int seconds = timeOut % 60;
            
            NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];
            dispatch_async(dispatch_get_main_queue(), ^{
                //設置界面的按鈕顯示 根據自己需求設置
                NSLog(@"____%@",strTime);
                [self setTitle:[NSString stringWithFormat:@"%@%@",strTime,waitTittle] forState:UIControlStateNormal];
                self.userInteractionEnabled = NO;
                
            });
            
            timeOut--;
            
        }
    });
    dispatch_resume(_timer);
    
}
@end

iOS倒計時