随机数

    一个小小的随机数工具。。。。。。。

self.view.backgroundColor = [UIColor yellowColor];
    
    UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(40, 40, 240, 60)];
    label.font = [UIFont boldSystemFontOfSize:30];
    label.text = @"点击开始随机";
    label.backgroundColor = [UIColor grayColor];
    label.textAlignment = NSTextAlignmentCenter;
    label.tag = 1;
    [self.view addSubview:label];
    [label release];
    
    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
    btn.frame = CGRectMake(120, 180, 80, 40);
    btn.backgroundColor = [UIColor grayColor];
    [btn setTitle:@"开始" forState:UIControlStateNormal];
    [btn setTitle:@"停止" forState:UIControlStateSelected];
    [btn addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:btn];
}

- (void)btnClick:(UIButton *)sender
{
    sender.selected = !sender.selected;
    
    if (sender.selected) {
        
        _timer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(timeRun) userInfo:nil repeats:YES];
        //启动时间器，让self每隔0.01秒执行一次timeRun
        
    } else {
        
        [_timer invalidate];
        //关闭时间器
    }
}

- (void)timeRun
{
    int row = arc4random_uniform(8)+1;
    int num = arc4random_uniform(11)+1;
    
    UILabel *label = (UILabel *)[self.view viewWithTag:1];
    //通过tag找view
    
    label.text = [NSString stringWithFormat:@"%d%02d",row,num];
}