NSDateComponents回归奇怪的时刻

Question

我正在编写一些代码来获取服务器上的图像.图像文件名采用yyyyMMdd_HHmm格式(UTC格式),每3小时生成一次(1200,1500,1800,...等).当代码开始时,我得到当前的UTC日期并提取时间.然后我从中创建一个NSDateComponent,并查看当前时间,将NSDateComponent的小时设置为下一个图像的小时.非常奇怪的是,如果我将小时设置为3,NSDate我从NSCalendar返回dateFromComponents有一个不同的时间 ...什么给出？(我也在控制台输出中添加了).

// get current time in UTC
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
NSTimeZone *UTC = [NSTimeZone timeZoneWithName:@"UTC"];
[dateFormatter setTimeZone:UTC];

//  get the current hour & min
[dateFormatter setDateFormat:@"HHmm"];
NSDate *today = [NSDate date];
NSString *str = [dateFormatter stringFromDate:today];
NSInteger hour = [str integerValue];
NSLog(str);

// find next image hour
NSCalendar *cal = [[NSCalendar alloc]   initWithCalendarIdentifier:NSGregorianCalendar];
unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit |  NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit;
NSDateComponents *currentImageDateComps = [cal components:unitFlags fromDate:today];

if (hour > 2100) {
    [currentImageDateComps setHour:0];
    // add an extra day as next image is start of new day
    [currentImageDateComps setDay:[currentImageDateComps day]+1];

} else if (hour < 300) {
    [currentImageDateComps setHour:3];
} else if (hour < 600) {
    [currentImageDateComps setHour:6];
} else if (hour < 900) {
    [currentImageDateComps setHour:9];
} else if (hour < 1200) {
    [currentImageDateComps setHour:12];
} else if (hour < 1500) {
    [currentImageDateComps setHour:15];
} else if (hour < 1800) {
    [currentImageDateComps setHour:18];
} else if (hour < 2100) {
    [currentImageDateComps setHour:21];
}
[currentImageDateComps setMinute:0];


NSLog(@"hour %d", [currentImageDateComps hour]);
NSLog(@"minute %d", [currentImageDateComps minute]);
// construct the date
NSDate *currentImageDate = [cal dateFromComponents:currentImageDateComps];
[dateFormatter setDateFormat:@"yyyyMMdd_hhmm"];
NSString *nextImage = [dateFormatter stringFromDate:currentImageDate];

self.currentFilename = [nextImage stringByAppendingString:@".png"];
NSLog(self.currentFilename);

从NSLogs生成的控制台输出就是这个.我得到的值为3小时,但它返回为'1700'？

2010-01-25 12:25:02.049 Forecast [8447:207] viewDidLoad

2010-01-25 12:25:02.052预测[8447:207] 0225

2010-01-25 12:25:02.052预测[8447:207]小时3

2010-01-25 12:25:02.053预测[8447:207]分钟0

2010-01-25 12:25:02.053 Forecast [8447:207] 20100124_1700.png

(我知道有一些内存释放问题,但我想先让它发挥功能..)

Answer 1

可能是时区问题？