"Learn iOS Path: objective-c" block syntax. NSDate and NSDateFormatter

I. Block blocks syntax

Block syntax: You can define anonymous functions inside a function

Format: ^ return value type (parameter list) {function Body} where return value type can be omitted

Block Simple Exercise :

①. To find the maximum value of two numbers

      int (^) (int,int)//block type         int (^max) (int,int) = ^ (int a,int b) {//block's implementation body                  return a > B? a:b;                  };                 int value = max (4,6); printf ("%d", value);

②. Converting an integer to a string object

        typedef void (^exchange) (int);        Exchange Change  = ^ (int number) {            NSString *string = [[NSString alloc] initwithformat:@ "%d", number];            NSLog (@ "%@", string);        };        Change (5);

③. Converting an integer to a Nsmumber object

     typedef  NSNumber * (^EXC) (int);        EXC Exchange = ^ NSNumber * (int number) {            return @ (number);        };       NSNumber *number = Exchange (5); NSLog (@ "%@", number);

④. Passing in a string object, returning all uppercase objects

      typedef nsstring * (^upper) (NSString *);        UPPER upperstring = ^nsstring * (nsstring *string) {            return [string uppercasestring];        };                NSString *temp = @ "SDSDFASDF";        NSString *num = upperstring (temp);        NSLog (@ "%@", num);

⑤ implements the number of OC array elements,

     typedef nsuinteger (^count) (Nsarray *);       Count GetCount = ^nsuinteger (Nsarray *arr) {            return [arr count];        };        Nsarray *ar1 = @[@ "SADF", @ "asdf", @ "DSFG", @ "FDG"];        Nsuinteger count = GetCount (AR1);        NSLog (@ "%ld", count);

⑥. Defining a block to achieve a comparison of two integers

        typedef nscomparisonresult (^compare) (int,int);        Compare Compare = ^nscomparisonresult (int a,int b) {            //return [@ (a) Compare: @ (b)];            Return a > B? Nsordereddescending:a = = b?                                         nsorderedsame:nsorderedascending;        };        Nscomparisonresult x =  compare (5,6);        NSLog (@ "%ld", x);//-1

⑦. Implementing a comparison of two string objects

     typedef nscomparisonresult (^comparestring) (nsstring *,nsstring *);        comparestring com = ^nscomparisonresult (nsstring *str1,nsstring *str2) {            return [str1 compare:str2];        };        NSString *TEMP1 = @ "dasf";        NSString *TEMP2 = @ "das35f";        Nscomparisonresult tem  = com (TEMP1,TEMP2);        NSLog (@ "%ld", tem);

⑧.block Implementing array sorting

    Nsarray *ar = @[@ "ads", @ "DD", @ "FF", @ "hh"];    Nsarray *ar1 = [ar sortedarrayusingcomparator:^ (id num1,id num2) {return-[nsstring        *] NUM1 Compare: (NSString *) num 2];    NSLog (@ "%@", AR1);

2.block relationship to local variables and global variables

    __block int num = 1; __block modified can modify the local variable    void (^addnum) () = ^void () {      int c = num *,//block internal can access the external local variable        num++;//internal access to local variables, but You cannot modify a local variable. If modified with __block, you can modify        printf ("%d", c);    };    Addnum ();

Two. NSDate and NSDateFormatter Common applications

①. Getting the time of the current 0 time zone

   NSDate *date = [NSDate date];   NSLog (@ "%@", date);

②. Get the time tomorrow

   NSDate *tomorrow = [nsdate datewithtimeintervalsincenow:60 * *];   NSLog (@ "%@", Tomorrow);

③ get yesterday's current time

  NSDate *yesterday = [nsdate datewithtimeintervalsincenow:-60 * *];  NSLog (@ "%@", yesterday)

④. By 1970/1/1, calculated at this time 2014/12/29

   NSDate *now = [nsdate dateWithTimeIntervalSince1970:                          (One * 366 + * 365) * * 3600 + 362 * * 3600];   NSLog (@ "%@", now);

⑤. Calculate the time by 2001/1/1//default 2001/1/1

  NSDate *now1 = [nsdate datewithtimeintervalsincereferencedate:                                (3 * 366 + one * 365) * * 3600-3 * + * 3600];  NSLog (@ "%@", Now1);

⑥. Get two time intervals

   Nstimeinterval interval = [date1 timeintervalsincedate:date2];   Double type nstimeinterval   NSLog (@ "%.1f", interval);

⑦. Compare dates sooner or later, return morning and evening dates

NSDate *dt1 = [Date1 earlierdate:date2]; NSDate *DT2 = [Date1 laterdate:date2]; NSLog (@ "%@", DT1); NSLog (@ "%@", DT2);

⑧. Determine if the dates are the same

  BOOL isequal = [Date1 isequaltodate:date2];        if (isequal) {            NSLog (@ "equals"),        } else {            NSLog (@ "Not equal");        }

Three. Date format class NSDateFormatter
①. Converts the NSDate object to a date string in the specified date format.

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

The code is as follows:

   NSDate *date = [NSDate date];   Gets the current time   nsdateformatter *formatter = [[NSDateFormatter alloc] init];   Set the format.  HH---Represents a 24-hour system, HH---represents 12-hour AA pm/am eee Tuesday  [Formatter setdateformat:@ "Yyyy-mm-dd HH:mm:ss eee AA"];  /[formatter setdateformat:@ "MM month DD day EEE aahh:mm"];   Conversion format NSString *string =[formatter stringfromdate:date]; NSLog (@ "%@", string);

2. Convert date string to NSDate object in the specified date format

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];    NSString *string1 = @ "May 01, 2014 10:53 18 sec";    NSLog (@ "%@", string1);    For NSDate objects, is always the time of the 0-time zone   //hh---represents the 24-hour system, HH---represents 12-hour system [formatter setdateformat:@ "yyyy years mm month DD Day HH point mm minutes ss seconds"];  NSDate *date1 = [Formatter datefromstring:string1]; NSLog (@ "%@", date1);

"Learn iOS Path: objective-c" block syntax. NSDate and NSDateFormatter