NSDateFormatter的作用

• NSString * -> NSDate *

- (nullable NSDate *)dateFromString:(NSString *)string;

• NSDate * -> NSString *

- (NSString *)stringFromDate:(NSDate *)date;

常見(jiàn)的日期格式

• http://www.cnblogs.com/mailingfeng/archive/2011/07/28/2120422.html

NSString * -> NSDate *

• 2017-6-01 15:10:05

// 時(shí)間字符串
NSString *string = @"2017-6-01 15:10:05";

// 日期格式化類
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
// 設(shè)置日期格式(為了轉(zhuǎn)換成功)
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";

// NSString * -> NSDate *
NSDate *date = [fmt dateFromString:string];

NSLog(@"%@", date);

• 6月-01號(hào)/2017年 15-10:05秒

// 時(shí)間字符串
NSString *string = @"6月-01號(hào)/2017年 15-10:05秒";

// 日期格式化類
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"MM月-dd號(hào)/yyyy年 HH-mm:ss秒";

NSLog(@"%@", [fmt dateFromString:string]);

• Tue May 31 17:46:55 +0800 2011

// 時(shí)間字符串
NSString *string = @"Tue May 31 17:46:55 +0800 2011";

// 日期格式化類
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"EEE MMM dd HH:mm:ss Z yyyy";
// fmt.dateFormat = @"EEE MMM dd HH:mm:ss ZZZZ yyyy";
// 設(shè)置語(yǔ)言區(qū)域(因?yàn)檫@種時(shí)間是歐美常用時(shí)間)
fmt.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];

NSLog(@"%@", [fmt dateFromString:string]);

• 1745645645645

// 時(shí)間戳 : 從1970年1月1號(hào) 00:00:00開(kāi)始走過(guò)的毫秒數(shù)

// 時(shí)間字符串 - 時(shí)間戳
NSString *string = @"1745645645645";
NSTimeInterval second = string.longLongValue / 1000.0;

// 時(shí)間戳 -> NSDate *
NSDate *date = [NSDate dateWithTimeIntervalSince1970:second];
NSLog(@"%@", date);

NSCalendar的注意點(diǎn)

#define iOS(version) ([UIDevice currentDevice].systemVersion.doubleValue >= (version))

NSCalendar *calendar = nil;
if ([UIDevice currentDevice].systemVersion.doubleValue >= 8.0) {
    calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
} else {
    calendar = [NSCalendar currentCalendar];
}

NSCalendar *calendar = nil;
if ([NSCalendar respondsToSelector:@selector(calendarWithIdentifier:)]) {
    calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
} else {
    calendar = [NSCalendar currentCalendar];
}

NSDate * -> NSString *

NSDate *date = [NSDate date];

NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy年MM月dd號(hào) HH:mm:ss";

NSString *string = [fmt stringFromDate:date];

獲得日期元素

NSString *string = @"2017-6-01 15:10:05";

NSString *month = [string substringWithRange:NSMakeRange(5, 2)];

NSLog(@"%@", month);

// 時(shí)間字符串
NSString *string = @"2017-6-01 15:10:05";

// 日期格式化類
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
// 設(shè)置日期格式(為了轉(zhuǎn)換成功)
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";

// NSString * -> NSDate *
NSDate *date = [fmt dateFromString:string];

// 利用NSCalendar處理日期
NSCalendar *calendar = [NSCalendar currentCalendar];
NSInteger month = [calendar component:NSCalendarUnitMonth fromDate:date];
NSInteger hour = [calendar component:NSCalendarUnitHour fromDate:date];
NSInteger minute = [calendar component:NSCalendarUnitMinute fromDate:date];

NSLog(@"%zd %zd %zd", month, hour, minute);

// 時(shí)間字符串
NSString *string = @"2017-6-01 15:10:05";

// 日期格式化類
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
// 設(shè)置日期格式(為了轉(zhuǎn)換成功)
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";

// NSString * -> NSDate *
NSDate *date = [fmt dateFromString:string];

// 利用NSCalendar處理日期
NSCalendar *calendar = [NSCalendar currentCalendar];

NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *cmps = [calendar components:unit  fromDate:date];

//    NSLog(@"%zd %zd %zd", cmps.year, cmps.month, cmps.day);
NSLog(@"%@", cmps);

日期比較

// 時(shí)間字符串
NSString *createdAtString = @"2017-6-01 15:10:05";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *createdAtDate = [fmt dateFromString:createdAtString];

// 手機(jī)當(dāng)前時(shí)間
NSDate *nowDate = [NSDate date];

/**
 NSComparisonResult的取值
 NSOrderedAscending = -1L, // 升序, 越往右邊越大
 NSOrderedSame,  // 相等
 NSOrderedDescending // 降序, 越往右邊越小
 */
// 獲得比較結(jié)果(誰(shuí)大誰(shuí)小)
NSComparisonResult result = [nowDate compare:createdAtDate];
if (result == NSOrderedAscending) { // 升序, 越往右邊越大
    NSLog(@"createdAtDate > nowDate");
} else if (result == NSOrderedDescending) { // 降序, 越往右邊越小
    NSLog(@"createdAtDate < nowDate");
} else {
    NSLog(@"createdAtDate == nowDate");
}

// 時(shí)間字符串
NSString *createdAtString = @"2017-6-01 15:10:05";
NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
NSDate *createdAtDate = [fmt dateFromString:createdAtString];

// 手機(jī)當(dāng)前時(shí)間
//    NSDate *nowDate = [NSDate date];

// 獲得createdAtDate和nowDate的時(shí)間間隔(間隔多少秒)
//    NSTimeInterval interval = [nowDate timeIntervalSinceDate:createdAtDate];
NSTimeInterval interval = [createdAtDate timeIntervalSinceNow];
NSLog(@"%f", interval);

NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";

// 時(shí)間字符串
NSString *createdAtString = @"2017-6-01 15:10:05";
NSDate *createdAtDate = [fmt dateFromString:createdAtString];

// 其他時(shí)間
NSString *otherString = @"2017-6-01 15:10:05";
NSDate *otherDate = [fmt dateFromString:otherString];

// 獲得NSCalendar
NSCalendar *calendar = nil;
if ([NSCalendar respondsToSelector:@selector(calendarWithIdentifier:)]) {
    calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
} else {
    calendar = [NSCalendar currentCalendar];
}

// 獲得日期之間的間隔
NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
NSDateComponents *cmps = [calendar components:unit fromDate:createdAtDate toDate:otherDate options:0];

NSLog(@"%@", cmps);

條件判斷的一些注意點(diǎn)

1.判斷一個(gè)數(shù)組中是否有具體內(nèi)容
1> 正確
if (array.count) {

}

2> 錯(cuò)誤
if (array) {

}

2.判斷一個(gè)字符串是否有具體內(nèi)容
1> 正確
if (string.length) {

}

2> 錯(cuò)誤
if (string) {

}