The path to ios: Objective-C block syntax. NSDate and NSDateFormatter, objective-c.nsdate

The path to ios: Objective-C block syntax. NSDate and NSDateFormatter, objective-c.nsdate

I. Block syntax

Block Syntax: anonymous functions can be defined within a function.

Format: ^ return value type (parameter list) {function body}. The return value type can be omitted.

Simple block exercises:

①. Calculate the maximum value of two numbers

// Int (^) (int, int) // block type int (^ max) (int, int) = ^ (int a, int B) {// return a> B? A: B ;}; int value = max (4, 6); printf ("% d", value );

②. Convert an integer into a string object

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

③. Convert an integer into an NSMumber object

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

4. Input A String object and return all objects in uppercase.

      typedef NSString *(^UPPER)(NSString *);        UPPER upperString = ^NSString *(NSString *string) {            return [string uppercaseString];        };                NSString *temp = @"sdsdfasdf";        NSString *num = upperString(temp);        NSLog(@"%@",num);

⑤ Calculate 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. Define a block to compare 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. 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);

Sort. block to sort Arrays

    NSArray *ar = @[@"ads",@"dd",@"ff",@"hh"];    NSArray *ar1 = [ar sortedArrayUsingComparator:^(id num1,id num2) {        return -[(NSString *)num1 compare: (NSString *)num2];    }];    NSLog(@"%@",ar1);

2. Relationship between block and local variables and global variables

_ Block int num = 1; // _ block after modification, you can modify the local Variable void (^ addNum) () = ^ void () {int c = num * 10; // The block can access the external local variable num ++. // The local variable is accessed internally, but the local variable cannot be modified. if _ block is used for modification, you can modify printf ("% d", c) ;}; addNum ();

Ii. Common NSDate and NSDateFormatter applications

①. Get the time of the current Zero Time Zone

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

②. Obtain the time of tomorrow at this time

   NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:60 * 60 * 24];   NSLog(@"%@",tomorrow);

③ Obtain the current time of yesterday

  NSDate *yesterday = [NSDate dateWithTimeIntervalSinceNow:-60 * 60 * 24];  NSLog(@"%@",yesterday)

④ Calculate the time at this time by 2014/12/1/29

   NSDate *now = [NSDate dateWithTimeIntervalSince1970:                          (11 * 366 + 33 * 365)* 24 * 3600 + 362 * 24 * 3600];   NSLog(@"%@",now);

⑤ Calculate the time at this time using 2001/1/1 // default: 2001/1/1

  NSDate *now1 = [NSDate dateWithTimeIntervalSinceReferenceDate:                                (3 * 366 + 11 * 365)* 24 * 3600 - 3 * 24 * 3600];  NSLog(@"%@",now1);

6. Get the two time intervals

NSTimeInterval interval = [date1 timeIntervalSinceDate: date2]; // NSTimeInterval NSLog of the double type (@ "%. 1f", interval );

7. Compare the morning and evening dates, and return the morning and evening dates

 NSDate *dt1 = [date1 earlierDate:date2]; NSDate *dt2 = [date1 laterDate:date2]; NSLog(@"%@",dt1); NSLog(@"%@",dt2);

Same. Determine if the date is the same

BOOL isEqual = [date1 is1_todate: date2]; if (isEqual) {NSLog (@ "equal");} else {NSLog (@ "not equal ");}

Iii. Date Format class NSDateFormatter
①. Convert the NSDate object into a date string according to the specified date format.

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

The Code is as follows:

NSDate * date = [NSDate date]; // obtain the current time NSDateFormatter * formatter = [[NSDateFormatter alloc] init]; // set the format. // HH --- indicates the 24-hour system, and hh --- indicates the 12-hour aa system. Afternoon/morning, EEE Tuesday [formatter setDateFormat: @ "yyyy-MM-dd HH: mm: ss EEE aa "];/[formatter setDateFormat: @" MM dd-month EEE aaHH: mm "]; // converts the format NSString * string = [formatter stringFromDate: date]; NSLog (@ "% @", string );

2. Convert the date string into an NSDate object according to the specified date format

NSDateFormatter * formatter = [[NSDateFormatter alloc] init]; NSString * string1 = @ ", January 1, May 01, 2014"; NSLog (@ "% @", string1 ); // For NSDate objects, the time is always zero time zone // HH --- indicates the 24-hour system, and hh --- indicates the 12-hour system [formatter setDateFormat: @ "MM-dd-yyyy HH: mm: ss seconds"]; NSDate * date1 = [formatter dateFromString: string1]; NSLog (@ "% @", date1 );