NSDateFormatter在设备上返回（null）但在模拟器上没有

Question

我目前正在将EST时区的计时器格式化为设备时区

一切都在模拟器上完美运行，定时器会转换，但是一旦我在设备上运行它，它只会返回(null)。

时间字符串看起来像11:00 AM ET

NSString *timeString = time.time;

timeString = [timeString stringByReplacingOccurrencesOfString:@" ET" withString:@""];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"hh:mma"];
NSDate* dateFromString = [dateFormatter dateFromString:timeString];


NSDateFormatter* df_utc = [[NSDateFormatter alloc] init];
[df_utc setTimeZone:[NSTimeZone timeZoneWithName:@"EST"]];
[df_utc setDateFormat:@"hh:mma"];

NSDateFormatter* df_local = [[NSDateFormatter alloc] init];
[df_local setTimeZone:[NSTimeZone localTimeZone]];
[df_local setDateFormat:@"hh:mma"];

NSString *ts_utc_string = [df_utc stringFromDate:dateFromString];
NSString *ts_local_string = [df_local stringFromDate:dateFromString];

NSLog(@"UTC TIME: %@",ts_utc_string);
NSLog(@"LOCAL TIME: %@",ts_local_string);

在设备上它是NSLogs（null），但在模拟器上它会记录时间。