注释dateFormate yyyy:年　　MM:月　　dd:日　　HH:24小时  hh:12小时　　mm:分钟　　ss:秒钟　　Z:时区

1.解决获取NSDate的时间不对

NSDate *nowDate = [NSDate date];
    
NSTimeZone *localTimeZone = [NSTimeZone localTimeZone];
NSInteger ti = [localTimeZone secondsFromGMTForDate:nowDate];
    
NSDate *newDate = [nowDate dateByAddingTimeInterval:ti];
NSLog(@"世界统一时间:%@ 当地时间:%@", nowDate, newDate);

1.获取当前时间的年月日时分秒

NSCalendar *calendar = [NSCalendar currentCalendar];

NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;

NSDateComponents *components = [calendar components:unit fromDate:[NSDate date]];

NSLog(@"年:%ld 月:%ld 日:%ld 时:%ld 分:%ld 秒:%ld",(long)components.year, (long)components.month, (long)components.day, (long)components.hour, (long)components.minute, (long)components.second);

2.比较两个时间之间的差值

NSDate *date1 = [NSDate date]; // 当前的日期

NSString *dateStr = @"2015-06-29 07:05:26 +0000";
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss Z";
NSDate *date2 = [formatter dateFromString:dateStr];  // 指定的日期

NSCalendar *calendar = [NSCalendar currentCalendar];
NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *components = [calendar components:unit fromDate:date1 toDate:date2 options:0];

NSLog(@"相差年:%ld 月:%ld 日:%ld 时:%ld 分:%ld 秒:%ld",(long)components.year, (long)components.month, (long)components.day, (long)components.hour, (long)components.minute, (long)components.second);

3.获取当前日期的那天在所在月份是星期几

方法1:

NSCalendar *calendar = [NSCalendar currentCalendar];

NSDateComponents *components = [[NSDateComponents alloc] init];
components.year = 2016;
components.month = 1;
components.day = 4;
    
NSDate *date = [calendar dateFromComponents:components];

NSUInteger index = [calendar ordinalityOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitWeekOfMonth forDate:[NSDate date]];
NSLog(@"--%lu", index);

注释1:代表星期日  2:代表星期一  3:代表星期二  4:代表星期三  5:代表星期四  6:代表星期五  7:代表星期六

方法2:(好像不行)

NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *components = [calendar components:NSCalendarUnitWeekOfMonth fromDate:[NSDate date]];
NSLog(@"---%ld", (long)components.weekOfMonth);