Question

我有以下（terible）方法不断检查当前时间，并且当达到特定时间（在这种情况下是午夜）时，NSLog语句运行一次以表示正在执行的某些操作：

- (void) checkTime {

while (true){

    NSAutoreleasePool *loopPool = [[NSAutoreleasePool alloc] init];

    NSDate *now = [[NSDate alloc] init];

    NSDateFormatter *outputFormatter = [[NSDateFormatter alloc] init];
    [outputFormatter setDateFormat:@"HH:mm"];

    NSString *nowDateString = [outputFormatter stringFromDate:now];

    if([nowDateString isEqualToString:@"00:00"]){
        NSLog(@"Store previous days data..");
        BOOL stillMidnight = YES;
        while(stillMidnight == YES){
            NSDate *latestNow = [[NSDate alloc] init];

            NSDateFormatter *latestOutputFormatter = [[NSDateFormatter alloc] init];
            [latestOutputFormatter setDateFormat:@"HH:mm"];

            NSString *latestString = [latestOutputFormatter stringFromDate:latestNow];
            //Check if it is still midnight
            if([latestString isEqualToString:@"00:01"]){
                //leave while
                stillMidnight = NO;
            }
        }
        NSLog(@"No longer midnight");
    }

    [loopPool drain];

}

}

上面的方法从applicationDidFinishLaunchingWithOption方法调用如下：

[self performSelectorInBackground:@selector(checkTime) withObject:nil];

此代码在午夜运行NSLog（@＆＃34;存储前几天的数据......＆＃34;），这是我需要的，但这个问题有更优雅的解决方案吗？

谢谢，

杰克

Answer 1

你会好起来的：

获取当前日期;
今天午夜时分锻炼身体;
在一天之后安排一次性定时器;和
重复

很容易安排一个重复计时器，该计时器首先使用（3）计算的日期和每24小时计算一次，但这将无法实现夏令时。所以，例如（直接在这里编码，未经测试）

- (void)scheduleNextTimedAction
{
    // get the date now and the calendar the user is using
    // (which will include their time zone, helpfully)
    NSDate *dateNow = [NSDate date];
    NSCalendar *relevantCalendar = [NSCalendar currentCalendar];

    // decompose the current date to components; we'll
    // just ask for month, day and year here for brevity;
    // check out the other calendar units to decide whether
    // that's something you consider acceptable
    NSDateComponents *componentsForNow =
         [relevantCalendar components:
                  NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit
                  fromDate:dateNow];

    // we could explicitly set the time to midnight now,
    // but since that's 00:00 it'll already be the value
    // in the date components per the standard Cocoa object
    // creation components, so...

    // get the midnight that last occurred
    NSDate *lastMidnight = [relevantCalendar dateFromComponents:componentsForNow];

    // can we just add 24 hours to that? No, because of DST. So...

    // create components that specify '1 day', however long that may be
    NSDateComponents *oneDay = [[NSDateComponents alloc] init];
    oneDay.day = 1;

    // hence ask the calendar what the next midnight will be
    NSDate *nextMidnight = [relevantCalendar
                 dateByAddingComponents:oneDay
                 toDate:lastMidnight
                 options:0];
    [oneDay release];

    // now create a timer to fire at the next midnight, to call
    // our periodic function. NB: there's no convenience factory
    // method that takes an NSDate, so we'll have to alloc/init
    NSTimer *timer = [[NSTimer alloc]
                 initWithFireDate:nextMidnight
                 interval:0.0 // we're not going to repeat, so...
                 target:self
                 selector:@selector(doTimedAction:)
                 userInfo:nil
                 repeats:NO];

    // schedule the timer on the current run loop
    [[NSRunLoop currentRunLoop]
                 addTimer:timer
                 forMode: NSDefaultRunLoopMode];

    // timer is retained by the run loop, so we can forget about it
    [timer release];
}

- (void)doTimedAction:(NSTimer *)timer
{
    NSLog(@"do action");
    [self scheduleNextTimedAction];
}

Answer 2

如果您想在任意时间点执行代码，最好设置本地通知。

Answer 3

如果计时器还应在您的应用未运行Push notification guide或NSTimer时提醒用户，则可以使用UILocalNotification，也可以使用触发日期或间隔进行初始化作为要调用的选择器。请注意，如果您的应用在后台，NSTimer将无法触发，但在这种情况下，相反会在您的应用再次激活时触发。

Objective-C每天在给定时间执行方法 - 杂乱的实现

3 个答案: