NSTimer定时器的用法

#import "ViewController.h"

@interface ViewController ()
{
    NSTimer *countDownTimer;
    int countDownTime;
}
@property (weak, nonatomic) IBOutlet UIButton *codeBtn;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (IBAction)getCodeBtnClick:(UIButton *)sender {

    [_codeBtn setEnabled:NO];
    if (countDownTimer)
    {
        [countDownTimer invalidate];
        countDownTimer=nil;
    }
    countDownTime=;
    countDownTimer=[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(countDown) userInfo:nil repeats:YES];

}
-(void)countDown
{
    countDownTime--;
    if (countDownTime==)
    {
        [countDownTimer invalidate];
        countDownTimer=nil;
        [_codeBtn setEnabled:YES];
        [_codeBtn setTitle:@"获取验证码" forState:UIControlStateNormal];
        return;
    }
    NSString *count=[NSString stringWithFormat:@"%d",countDownTime];
    NSMutableAttributedString *attributeString=[[NSMutableAttributedString alloc]initWithString:[NSString stringWithFormat:@"剩余%@秒",count]];
    [attributeString addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(,count.length)];
    [_codeBtn setAttributedTitle:attributeString forState:UIControlStateDisabled];

}