iOS开发NSDate的api

/*  NSDate.h
    Copyright (c) 1994-2017, Apple Inc. All rights reserved.
*/

#import 
#import 

@class NSString;

NS_ASSUME_NONNULL_BEGIN

FOUNDATION_EXPORT NSNotificationName const NSSystemClockDidChangeNotification API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0));

typedef double NSTimeInterval;

#define NSTimeIntervalSince1970  978307200.0

@interface NSDate : NSObject 

@property (readonly) NSTimeInterval timeIntervalSinceReferenceDate;

- (instancetype)init NS_DESIGNATED_INITIALIZER;
- (instancetype)initWithTimeIntervalSinceReferenceDate:(NSTimeInterval)ti NS_DESIGNATED_INITIALIZER;
- (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;

@end

@interface NSDate (NSExtendedDate)

- (NSTimeInterval)timeIntervalSinceDate:(NSDate *)anotherDate;
@property (readonly) NSTimeInterval timeIntervalSinceNow;
@property (readonly) NSTimeInterval timeIntervalSince1970;

- (id)addTimeInterval:(NSTimeInterval)seconds API_DEPRECATED("Use dateByAddingTimeInterval instead", macos(10.0,10.6), ios(2.0,4.0), watchos(2.0,2.0), tvos(9.0,9.0));
- (instancetype)dateByAddingTimeInterval:(NSTimeInterval)ti API_AVAILABLE(macos(10.6), ios(2.0), watchos(2.0), tvos(9.0));

- (NSDate *)earlierDate:(NSDate *)anotherDate;
- (NSDate *)laterDate:(NSDate *)anotherDate;
- (NSComparisonResult)compare:(NSDate *)other;
- (BOOL)isEqualToDate:(NSDate *)otherDate;

@property (readonly, copy) NSString *description;
- (NSString *)descriptionWithLocale:(nullable id)locale;

@property (class, readonly) NSTimeInterval timeIntervalSinceReferenceDate;

@end

@interface NSDate (NSDateCreation)

+ (instancetype)date;
+ (instancetype)dateWithTimeIntervalSinceNow:(NSTimeInterval)secs;
+ (instancetype)dateWithTimeIntervalSinceReferenceDate:(NSTimeInterval)ti;
+ (instancetype)dateWithTimeIntervalSince1970:(NSTimeInterval)secs;
+ (instancetype)dateWithTimeInterval:(NSTimeInterval)secsToBeAdded sinceDate:(NSDate *)date;

@property (class, readonly, copy) NSDate *distantFuture;
@property (class, readonly, copy) NSDate *distantPast;

- (instancetype)initWithTimeIntervalSinceNow:(NSTimeInterval)secs;
- (instancetype)initWithTimeIntervalSince1970:(NSTimeInterval)secs;
- (instancetype)initWithTimeInterval:(NSTimeInterval)secsToBeAdded sinceDate:(NSDate *)date;

@end

NS_ASSUME_NONNULL_END
```objective-c