__block int timeout=60;

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); //每秒执行
dispatch_source_set_event_handler(_timer, ^{
    if(timeout<=0){
        dispatch_source_cancel(_timer);
        dispatch_async(dispatch_get_main_queue(), ^{
            
            [self.validBtn setTitle:@"获取短信验证码" forState:UIControlStateNormal];
            //self.validBtn.backgroundColor=RGB(120, 0, 103);
            [self.validBtn setBackgroundImage:[UIImage imageNamed:@"获取验证码"] forState:UIControlStateNormal];
            self.validBtn.userInteractionEnabled = YES;
        });
    }else{
        int seconds = timeout;
        NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];
        dispatch_async(dispatch_get_main_queue(), ^{
            
            [self.validBtn setTitle:[NSString stringWithFormat:@"%@秒",strTime] forState:UIControlStateNormal];
            //self.validBtn.backgroundColor=RGB(207, 207, 207);
            [self.validBtn setBackgroundImage:[UIImage imageNamed:@"获取验证码-不可点击"] forState:UIControlStateNormal];
            self.validBtn.userInteractionEnabled = NO;
        });
        timeout--;
    }
});
dispatch_resume(_timer);