Convert GMT NSDate to device's current Time Zone

Question

I\'m using Parse.com to store some values:

These are GMT values. How d

Answer 1

Creating an Xcode test case like the following may help us remember the rules "forever":

- (void)test2015_05_23_07_07_07_Toronto {
    NSString *utcDateString = @"2015_05_23 12:07:07";
    NSDateFormatter *dateFormatter = [NSDateFormatter new];
    dateFormatter.dateFormat = @"yyyy_MM_dd HH:mm:ss";

    dateFormatter.timeZone = [NSTimeZone timeZoneWithName:@"UTC"];
    NSDate *date2015_05_23_12_07_07_UTC = [dateFormatter dateFromString:utcDateString];

    XCTAssertTrue([date2015_05_23_12_07_07_UTC.description isEqualToString:@"2015-05-23 12:07:07 +0000"]);

    dateFormatter.timeZone = [NSTimeZone timeZoneWithName:@"EST"];
    NSString *torontoDateString = [dateFormatter stringFromDate:date2015_05_23_12_07_07_UTC];
    XCTAssertTrue([torontoDateString isEqualToString:@"2015_05_23 07:07:07"]);

    // change format to add ZZZ
    dateFormatter.dateFormat = @"yyyy_MM_dd HH:mm:ss ZZZ";
    torontoDateString = [dateFormatter stringFromDate:date2015_05_23_12_07_07_UTC];
    XCTAssertTrue([torontoDateString isEqualToString:@"2015_05_23 07:07:07 -0500"]);

    XCTAssertEqual(1432382827, [date2015_05_23_12_07_07_UTC timeIntervalSince1970]);

    NSCalendar *calendar = [NSCalendar autoupdatingCurrentCalendar];
    calendar.timeZone = [NSTimeZone timeZoneWithName:@"EST"];
    NSDateComponents *components = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond) fromDate:date2015_05_23_12_07_07_UTC];
    XCTAssertEqual(2015, components.year);
    XCTAssertEqual(5, components.month);
    XCTAssertEqual(23, components.day);
    XCTAssertEqual(7, components.hour);
    XCTAssertEqual(7, components.minute);
    XCTAssertEqual(7, components.second);
}