_timerBtn.titleLabel.text = [NSString stringWithFormat:@"%ld秒",scondes];
[_timerBtn setTitle:[NSString stringWithFormat:@"%ld秒",scondes] forState:UIControlStateNormal];
两个方法的次序不能改变
_timerBtn.titleLabel.text = [NSString stringWithFormat:@"%ld秒",scondes];
[_timerBtn setTitle:[NSString stringWithFormat:@"%ld秒",scondes] forState:UIControlStateNormal];
两个方法的次序不能改变