ios - NSString 和 NSDate 的减法和转换

Question

我有以下代码:

NSString *startDate = @"2014-09-29 05:46:34 +000";

// Format the string
NSRange range = NSMakeRange(0, 19);
startDate = [startDate substringWithRange:range];

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSDate *dateFromString = [[NSDate alloc] init];
dateFromString = [dateFormatter dateFromString:startDate];

NSDate *trendDate = [dateFromString dateByAddingTimeInterval:-3600*12];

NSString *dateString = [NSString stringWithFormat:@"%@", trendDate];

然后我的日期字符串结束为:

@"2014-09-29 00:46:34 +000";

为什么只减去 5 小时而不是 12 小时？

Answer 1

不是从 startDate 字符串中获取子字符串，而是尝试这种日期格式:

dateFormatter.dateFormat = @"yyyy-MM-dd HH:mm:ss ZZZ"

然后

dateFromString = [dateFormatter dateFromString:startDate];

NSDate *trendDate = [dateFromString dateByAddingTimeInterval:-3600*12];

NSString *dateString = [dateFormatter stringFromDate:trendDate];