Common classes under the Foundation framework: NSNumber, NSDate, NSCalendar, NSDateFormatter, NSNull, NSKeyedArchiver, nsnumbernsdate

Common classes under the Foundation framework: NSNumber, NSDate, NSCalendar, NSDateFormatter, NSNull, NSKeyedArchiver, nsnumbernsdate

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Common classes under the Foundation framework

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1. [NSNumber]

[Note] basic data types such as int, float, char, and double are used.

[Note] basic variable types inherited from C language (int, float, char, double, etc.) cannot be added to the oc-specific data structures such as arrays and dictionaries. It is inconvenient to use, and cannot be managed by adding categories and other oc proprietary syntaxes.

[Also] It can be considered that NSNumber is a class for converting basic data to object data.

[Note] NSNumber is a class. This class is used to convert the basic data type into a class of the object data type.

[Note] You can first save the basic data type to the nsnumber object, and then store the nsnumber into an array or dictionary.

[Note] What NSNumber can do can be replaced by NSString. Therefore, NSString is more commonly used.

 

2. [NSDate]

[Note] NSDate is a date (time) class.

[Note] the difference in time zone is 8 hours.

 

Limit 1 // create NSDate at the current time

NSDate * myDate = [NSDate date];

NSLog (@ "myDate = % @", myDate );

Listen 2 // 24 hours from now on

NSTimeInterval secondsPerDay = 24*60*60;

NSDate * tomorrow = [NSDate dateWithTimeIntervalSinceNow: secondsPerDay];

NSLog (@ "myDate = % @", tomorrow );

3 // create date based on the existing date

NSTimeInterval secondsPerDay1 = 24*60*60;

NSDate * now = [NSDate date];

NSDate * yesterDay = [now addTimeInterval:-secondsPerDay1];

NSLog (@ "yesterDay = % @", yesterDay );

4.1.4 // Date of comparison

BOOL sameDate = [now is1_todate: yesterDay];

NSLog (@ "sameDate = % lu", sameDate );

Limit 4.1 // obtain an earlier date

NSDate * earlierDate = [yesterDay earlierDate: now];

NSLog (@ "earlierDate = % @", earlierDate );

Limit 4.2 // a later date

NSDate * laterDate = [yesterDay laterDate: now];

NSLog (@ "laterDate = % @", laterDate );

Iii. NSCalendar

// Create a date using the NSCALENDAR class

// You can use the NSCalendar class to create a specified date.

NSDateComponents * comp = [[NSDateComponents alloc] init];

[Comp setMonth: 06];

[Comp setDay: 01];

[Comp setyear: 2001];

[Comp setHour: 24];

NSCalendar * myCal = [[NSCalendar alloc] initWithCalendarIdentifier: NSGregorianCalendar];

NSDate * myDate1 = [myCal dateFromComponents: comp];

NSLog (@ "myDate1 =%@", myDate1 );

 

// Obtain the date from the existing date

NSCalendar * myCal = [[NSCalendar alloc] initWithCalendarIdentifier: NSGregorianCalendar];

Unsigned units = NSMonthCalendarUnit | NSDayCalendarUnit | NSYearCalendarUnit;

NSDateComponents * comp1 = [myCal components: units fromDate: [NSDate date];

NSInteger month = [comp1 month];

NSInteger year = [comp1 year];

NSInteger day = [comp1 day];

 

Delta 4 [NSDateFormatter] format date class

 

Some formats of NSDateFormatter

// Instantiate an NSDateFormatter object

NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init];

// Set the time format, which can be set as needed

[DateFormatter setDateFormat: @ "yyyy-MM-dd HH: mm: ss"];

// Use [NSDate date] to obtain the current system time

NSString * currentDateStr = [dateFormatter stringFromDate: [NSDate date];

// Output format: 13:22:13

NSLog (@ "% @", currentDateStr );

 

Custom format

// The formatter format should be noted here. If it is a lowercase "hh", the time will be changed to 12 hours or 24 hours. In upper case, the value is in the 24-hour format.

[DateFormatter setDateFormat: @ "yyyy-MM-dd HH: mm: ss"];

[DateFormatter setDateFormat: @ "MM dd, yyyy # EEEE"]; // EEEE indicates the day of the week and EEE indicates the day of the week.

[DateFormatter setDateFormat: @ "yyyy-MM-dd HH: mm: ss"];

[DateFormatter setDateFormat: @ "MMMMd, yyyy"]; // MMMM is a month of xx, and a d can save the value of 0 before 01

 

The output format is set by setDateStyle and setTimeStyle. the date and time formats defined respectively are optional.

Typedef enum {

NSDateFormatterNoStyle = kCFDateFormatterNoStyle,

Nsdateformatter1_style = kcfdateformatter1_style, // "11/23/37" or"

NSDateFormatterMediumStyle = kCFDateFormatterMediumStyle, // \ "Nov 23,193 7 \"

NSDateFormatterLongStyle = kCFDateFormatterLongStyle, // \ "November 23,193 7" or "3:30:32 \"

NSDateFormatterFullStyle = kCFDateFormatterFullStyle // "Tuesday, rjl 12,195 2 AD" or "3:30:42 PST"

} NSDateFormatterStyle;

 

V. Date comparison

The following methods are available for comparison between dates:

-(BOOL) is1_todate :( NSDate *) otherDate;

YES is returned for comparison with otherDate.

 

-(NSDate *) earlierDate :( NSDate *) anotherDate;

Returns the date earlier than anotherDate.

 

-(NSDate *) laterDate :( NSDate *) anotherDate;

Returns the date later than anotherDate.

 

-(NSComparisonResult) compare :( NSDate *) other;

This method is called for sorting:

. NSOrderedSame is returned when the date value saved by the instance and anotherDate are the same.

. NSOrderedDescending is returned when the date value saved by the instance is later than anotherDate.

. NSOrderedAscending is returned when the date value saved by the instance is earlier than anotherDate.

 

6. NSDate to NSString Conversion

// Convert NSDate to NSString and extract the month

NSString * time = [[NSString alloc] initWithFormat: @ "% @", myDate1];

NSLog (@ "% @", time );

Nsange range = {5, 2 };

NSLog (@ "month: % @", [time substringWithRange: range]);

 

Delta 7.IOS-NSDateDifference8Hours 

// Method 1

-(Void) tDate

{

NSDate * date = [NSDatedate];

NSTimeZone * zone = [NSTimeZonesystemTimeZone];

NSInteger interval = [zone secondsFromGMTForDate: date];

NSDate * localeDate = [date dateByAddingTimeInterval: interval];

NSLog (@ "% @", localeDate );

}

// Method 2

+ (NSString *) fixStringForDate :( NSDate *) date

{

NSDateFormatter * dateFormatter = [[NSDateFormatteralloc] init];

[DateFormatter setDateStyle: kCFDateFormatterFullStyle];

[DateFormatter setDateFormat: @ "yyyy-MM-dd HH: mm: ss"];

NSString * fixString = [dateFormatter stringFromDate: date];

[DateFormatter release];

Return fixString;

}

 

△△[ NSNull]

[Note] There are four empty things

[NULL] [nil] [Nil] [NSNull]

 

NULL: indicates that the base type pointer is NULL.

Int * p = NULL;

 

Nil: indicates that the object pointer is null.

Id obj = nil;

 

Nil: indicates that the Class variable is empty.

Class class = Nil;

 

NSNull: Used as a null element in data structures such as array dictionaries.

// Unique method

[NSNull null]; creates an object that indicates null

 

8. Archive NSKeyedArchiver

// Creates an array and initializes some data.

NSArray * array = [[NSArray alloc] initWithObjects: @ "zhangsan", @ "lisi", @ "wanger", @ "xiaoming", nil];

// Specify the name and path of the file to be saved.

// NSHomeDirectory () is the home path of the current system

// StringByAppendingPathComponent: Add a file named file.

// The file type can be left empty. The file name and suffix are random.

NSString * filePath = [NSHomeDirectory () stringByAppendingPathComponent: @ "file.txt"];

NSLog (@ "archive file path: % @", filePath );

// The NSKeyedArchiver class is used for archiving.

// The returned value indicates whether the archive is successful.

BOOL isSuccess = [NSKeyedArchiver archiveRootObject: array toFile: filePath];

If (isSuccess = YES ){

NSLog (@ "file saved successfully ");

}

// [Note] files archived in this way are encrypted and cannot be opened.

// Archive

NSArray * Arr = [NSKeyedUnarchiver unarchiveObjectWithFile: filePath];

NSLog (@ "The retrieved data is: % @", Arr );

[Read the official documentation]

[Note] It is recommended that you read the official Xcode documentation. The official documentation is very standard and there is no error.

// Disadvantage:

1. Poor readability. (Do not understand) (official documents are concise)

2. There are few examples, and there is little reference to the demo.

 

// Advantages

1. Rigorous knowledge.

2. You can find the answer in some special (difficult) official documents (provided that you spend time reading and searching)

[Solution to programming problems]

1. You can use Baidu first.

2. Go to Google. (Google Answers 99% English documents, which can be consulted with youdao dictionary)

3. Consult with colleagues.

4. Please refer to the official documentation.

5. See the youdao dictionary.