创建一个文件，并写入当前时间

AppDelegate.m

WriteDate *date = [[WriteDate alloc] init];

[date runAction];
WriteDate.h

{
NSInteger _index;
}

- (void)runAction;

WriteDate.m
@implementation WriteDate
{
NSString *path;
}

- (void)runAction
{
_index = 0;
//创建文件的路径
path = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Date.text"];
//开启定时器
[NSTimer scheduledTimerWithTimeInterval:1
target:self
selector:@selector(timeAction:)
userInfo:NULL
repeats:YES];

}

- (void)timeAction:(NSTimer *)time
{
//创建当前的日期对象
NSDate *date = [NSDate date];
//格式：2012/02/14 05:20:00
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
//设置格式
[dateFormatter setDateFormat:@"yyyy/MM/dd HH:mm:ss zz"];
NSString *dateString = [dateFormatter stringFromDate:date];
//创建文件的路径
// NSString *path = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Date.text"];

//读取文件中的数据
NSString *fileDate = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];

if (fileDate != nil)
{
dateString = [dateString stringByAppendingFormat:@"\n%@",fileDate];
}

[dateString writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:nil];

_index ++;

if (_index == 10)
{
//停止计时器
[time invalidate];
}

}