+(NSString*)date2str:(NSDate*)myNSDateInstance onlyDate:(BOOL)onlyDate{
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    if (onlyDate) {
        [formatter setDateFormat:@"yyyy-MM-dd"];
    }else{
        [formatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
    }

    //Optionally for time zone conversions
    //   [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"..."]];

    NSString *stringFromDate = [formatter stringFromDate:myNSDateInstance];
    return stringFromDate;
}

+(NSDate*)str2date:(NSString*)dateStr{
    if ([dateStr isKindOfClass:[NSDate class]]) {
        return (NSDate*)dateStr;
    }

    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat:@"yyyy-MM-dd"];
    NSDate *date = [dateFormat dateFromString:dateStr];
    return date;
}

网络上有很多NSDate的助手，我倾向于使用:

https://github.com/billymeltdown/nsdate-helper/

自述摘录如下:

  NSString *displayString = [NSDate stringForDisplayFromDate:date];

这将产生以下类型的输出:

‘3:42 AM’ – if the date is after midnight today
‘Tuesday’ – if the date is within the last seven days
‘Mar 1’ – if the date is within the current calendar year
‘Mar 1, 2008’ – else ;-)

swift格式:

func dateFormatterWithCalendar(calndarIdentifier: Calendar.Identifier, dateFormat: String) -> DateFormatter {

    let formatter = DateFormatter()
    formatter.calendar = Calendar(identifier: calndarIdentifier)
    formatter.dateFormat = dateFormat

    return formatter
}


//Usage
let date = Date()
let fotmatter = dateFormatterWithCalendar(calndarIdentifier: .gregorian, dateFormat: "yyyy")
let dateString = fotmatter.string(from: date)
print(dateString) //2018

iOS 15更新

iOS 15现在支持直接在Date对象上调用.格式化，而不需要显式的DateFormatter。

常见格式示例

文档

date.formatted() // 6/8/2021, 7:30 PM
date.formatted(date: .omitted, time: .complete) // 19:30
date.formatted(date: .omitted, time: .standard) // 07:30 PM
date.formatted(date: .omitted, time: .shortened) // 7:30 PM
date.formatted(date: .omitted, time: .omitted)

替代语法

文档

// We can also specify each DateComponent separately by chaining modifiers.
date.formatted(.dateTime.weekday(.wide).day().month().hour().minute())
// Tuesday, Jun 8, 7:30 pm

// Answer to specific question
date.formatted(.dateTime.year())

#ios #swift #convertDateinString

简单地像这样按你传递的格式“将日期转换为字符串”:

let formatter = DateFormatter()

formatter.dateFormat = "dd-MM-YYYY" // pass formate here
        
let myString = formatter.string(from: date) // this will convert Date in String

注意:你可以指定不同的格式，如"yyyy-MM-dd"， "yyyy"， "MM"等。

如果你没有NSDate -descriptionWithCalendarFormat:timeZone:locale: available(我不相信iPhone/Cocoa Touch包括这个)，你可能需要使用strftime和一些c风格的字符串。您可以使用NSDate -timeIntervalSince1970从NSDate中获取UNIX时间戳。