一、字符串转化成日期：
NSString *str = @"2017-10-21 23:00:11 +0800";
// 1.创建一个时间格式化对象
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
// 2.格式化对象的样式
formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss Z";
// 3.格式化让字符串转换成时间
NSDate *datestr = [formatter dateFromString:str];
// 4.自己给定的时间
NSDate *currentDate = datestr;
二、获取当月天数：
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
//此处是查看当前月的天数
NSDate *timeDate = [NSDate date];
NSRange range = [calendar rangeOfUnit:NSDayCalendarUnit inUnit: NSMonthCalendarUnit forDate:timeDate];
NSInteger countInteger = range.length;
NSLog(@"当月天数为:%lu",(unsigned long)countInteger);
三、获取指定日期是周几
NSDate *datestr = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian]; // 指定日历的算法
NSDateComponents *comps = [calendar components:NSCalendarUnitWeekday fromDate:datestr];
// 1:周日,2:周一 ,3.周二 ...以此类推
NSLog(@"今天是：%@",@([comps weekday]));
四、判断指定时间与当前时间大小
// 时间字符串
NSString *starTime= @"2017-23-20 11:10:05";
NSDateFormatter *format = [[NSDateFormatter alloc] init];
format.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *currentTime = [format dateFromString:starTime];
// 当前时间
NSDate *nowTime = [NSDate date];
// 获得比较结果(谁大谁小)
NSComparisonResult result = [nowTime compare:currentTime];
if (result == NSOrderedAscending) {
// 升序, 越往右边越大
NSLog(@"创建时间大于当前时间");
} else if (result == NSOrderedDescending) {
// 降序, 越往右边越小
NSLog(@"创建时间小于当前时间");
} else {
NSLog(@"创建时间等于当前时间");
}
五、获取年月日星期时分秒
NSDate* date = [NSDate date];
NSCalendar * calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
// NSDateComponent 可以获得日期的详细信息，即日期的组成
NSDateComponents *comps = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay|NSCalendarUnitHour|NSCalendarUnitMinute|NSCalendarUnitSecond|NSCalendarUnitWeekOfMonth|NSCalendarUnitWeekday fromDate:date];
NSLog(@"年 = year = %ld",comps.year);
NSLog(@"月 = month = %ld",comps.month);
NSLog(@"日 = day = %ld",comps.day);
NSLog(@"时 = hour = %ld",comps.hour);
NSLog(@"分 = minute = %ld",comps.minute);
NSLog(@"秒 = second = %ld",comps.second);
NSLog(@"星期 =weekDay = %ld ",comps.weekday);
//字符串类型 转化为 时间
NSString *string = @"1481706995000";
NSTimeInterval time = [string doubleValue] ;
NSDate *date = [[NSDate alloc]initWithTimeIntervalSince1970:time/1000.0];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSLog(@"转换的时间为：%@",[dateFormatter stringFromDate:date]);
输出：
转换的时间为：2016-12-14 17:56:35
记录两次请求前后时间差：
NSDate *date1 = [NSDate date];
NSDate *date2 = [NSDate date];
NSTimeInterval a = [date2 timeIntervalSince1970] - [date1 timeIntervalSince1970];
NSLog(@"A与B之间相差%.3f秒",a);
时间戳 时间 互换
//时间戳 -> 时间
NSDateFormatter *tmpFormatter = [[NSDateFormatter alloc] init];
[tmpFormatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
[tmpFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"Asia/Beijing"]];
NSDate *tmpTimedate = [NSDate dateWithTimeIntervalSince1970:tmpTime];
_mStrTime = [tmpFormatter stringFromDate:tmpTimedate];
参考：
+(NSString *)timestampSwitchTime:(NSInteger)timestamp andFormatter:(NSString *)format{
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateStyle:NSDateFormatterMediumStyle];
[formatter setTimeStyle:NSDateFormatterShortStyle];
[formatter setDateFormat:format]; // （@"YYYY-MM-dd hh:mm:ss"）----------设置你想要的格式,hh与HH的区别:分别表示12小时制,24小时制
NSTimeZone *timeZone = [NSTimeZone timeZoneWithName:@"Asia/Beijing"];
[formatter setTimeZone:timeZone];
NSDate *confromTimesp = [NSDate dateWithTimeIntervalSince1970:timestamp];
NSLog(@"1296035591 = %@",confromTimesp);
NSString *confromTimespStr = [formatter stringFromDate:confromTimesp];
//NSLog(@"&&&&&&&confromTimespStr = : %@",confromTimespStr);
return confromTimespStr;
}