NSDate常用

标签（空格分隔）： 实用编程习惯-coding

[TOC]

1、字符串与日期的相互转换

        //NSDate求日期
        NSDate *date = [NSDate date];
        NSDateFormatter *fm = [[NSDateFormatter alloc] init];
        fm.dateFormat = @"yyyy-MM-dd HH-mm-ss";
        //-----日期转换成字符串------
        NSDate *lastDate = [NSDate dateWithTimeInterval:-24*60*60 sinceDate:date];
        NSString *dateString = [fm stringFromDate:lastDate];
        NSLog(@"一天前的日期string :%@",dateString);

        //-----字符串转换成日期------
        NSString *oneDateString = @"2022-12-6 18:01:33";
        fm.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0];
        NSDate *oneDate = [fm dateFromString:oneDateString];

        NSLog(@"未来某天的日期Obj :%@",oneDate);

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2、NSDateComponents获取日期

NSCalendar *calendar = [NSCalendar currentCalendar];
        NSDate *date = [NSDate date];
        //日历集合的结构体
        NSCalendarUnit units = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
        NSDateComponents *comp = [calendar components:units fromDate:date];
        NSLog(@"%@",comp);
        NSLog(@"%zd年%zd月%zd日",comp.year,comp.month,comp.day);

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3 获取前一天或者后一天的日期

最low的方式

• 使用NSDateFormatter减去日期对应的秒数，不过这样，日期天数很多的时候，秒数就几千几万了，所以推荐使用日历里面的日期集合

高b格方式

        NSCalendar *calendar = [NSCalendar currentCalendar];
        NSDate *date = [NSDate date];
        //日历集合的结构体
        NSCalendarUnit units = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;

        NSDateComponents *components = [[NSDateComponents alloc] init];
        [components setYear:-1];
        [components setMonth:-1];
        NSDate *lastMonth = [calendar dateByAddingComponents:components toDate:date options:kNilOptions];
        components = [calendar components:units fromDate:lastMonth];
        NSLog(@"去年的 上一个月 %@",components);

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