Explore Public Snippets

+ (void)loadDataWithSaveToDB:(void(^)(NSString *itemListId,
                                      NSArray<NSDictionary *> *dictionaries,
                                      void(^saveCompletion)(NSError *error)))saveToDB
                  completion:(void(^)(NSError *error))completion {
    dispatch_group_t group = dispatch_group_create();
    void(^saveCompletion)(NSError *error) = ^(NSError *error){
        dispatch_group_leave(group);
    };
    __block NSError *completionError = nil;
    [self _processAllItemsStartingFromPage:1
                   withPreRequestPageBlock:
     ^{
         dispatch_group_enter(group);
     } requestCompletionBlock:^(NSArray<NSDictionary *> *dictionaries, NSError *error) {
         if (nil != error) {
             completionError = error;
         }
         if (nil != saveToDB) {
             saveToDB([self relatedItemListId], dictionaries, saveCompletion);
         }
     }];
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        if (nil != completion) {
            completion(completionError);
        }
    });
}

#pragma mark - Private
+ (void)_processAllItemsStartingFromPage:(NSInteger)page
                 withPreRequestPageBlock:(void(^)())preRequestBlock
                  requestCompletionBlock:(void(^)(NSArray<NSDictionary *> *dictionaries,
                                                  NSError *error))requestCompletion {
    if (nil != preRequestBlock) {
        preRequestBlock();
    }
    [self _requestPreItemsForPage:page completion:^(NSArray<DLNewsItem *> *items,
                                                    NSError *error) {
        if (nil == error) {
            // first request next page
            if (items.count == kItemsPerPage) {
                [self _processAllItemsStartingFromPage:page + 1
                               withPreRequestPageBlock:preRequestBlock
                                requestCompletionBlock:requestCompletion];
            }
            // then save items for current page
            [self _processNewsItems:items withCompletion:requestCompletion];
        } else {
            if (nil != requestCompletion) {
                requestCompletion(nil, error);
            }
        }
    }];
}

+ (void)_processNewsItems:(NSArray<DLNewsItem *> *)items
          withCompletion:(void(^)(NSArray<NSDictionary *> *dictionaries, NSError *error))completion {
    NSArray<NSDictionary *> *dictionaries = [items valueForKey:@"dictionaryRepresentation"];
    if (nil != completion) {
        completion(dictionaries, nil);
    }
}

NSString *trimmedString = [string stringByTrimmingCharactersInSet:
                                  [NSCharacterSet whitespaceCharacterSet]];
                                  
// per rimuovere anche newLine usare whitespaceAndNewlineCharacterSet

BOOL canOpenSettings = (&UIApplicationOpenSettingsURLString != NULL);
if (canOpenSettings) {
  NSURL *settingsURL = [NSURL URLWithString:UIApplicationOpenSettingsURLString];
  [[UIApplication sharedApplication] openURL:settingsURL];
}

=> Objective-C:
-(NSString *)getCurrentTime {
    
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setTimeStyle:NSDateFormatterShortStyle];
    NSString *currentTime = [dateFormatter stringFromDate:[NSDate date]];

    return currentTime;
    
}

To call this method within the same class:
NSString *time = [self getCurrentTime];
NSLog(@"%@",time);
//Results in the getCurrentTime function being called and the current time printed to the console.


=> Swift 
In Swift, we include the return arrow “->” which specifies that the function will return and the type of object that will be returned (String).
    func getCurrentTime() -> String {
        
        let date = NSDate()
        let formatter = NSDateFormatter()
        formatter.timeStyle = .ShortStyle
        var stringValue = formatter.stringFromDate(date)
        
        return stringValue
        
    }
    
To call this method within the same class:
let time = getCurrentTime()
println(time)
//Results in the getCurrentTime function being called and the current time printed to the console.

Using modular multiplication rules:
i.e. A^2 mod C = (A * A) mod C = ((A mod C) * (A mod C)) mod C
We can use this to calculate 7^256 mod 13 quickly
7^1 mod 13 = 7
7^2 mod 13 = (7^1 *7^1) mod 13 = (7^1 mod 13 * 7^1 mod 13) mod 13
We can substitute our previous result for 7^1 mod 13 into this equation.
7^2 mod 13 = (7 *7) mod 13 = 49 mod 13 = 10
7^2 mod 13 = 10
7^4 mod 13 = (7^2 *7^2) mod 13 = (7^2 mod 13 * 7^2 mod 13) mod 13
We can substitute our previous result for 7^2 mod 13 into this equation.
7^4 mod 13 = (10 * 10) mod 13 = 100 mod 13 = 9
7^4 mod 13 = 9
7^8 mod 13 = (7^4 * 7^4) mod 13 = (7^4 mod 13 * 7^4 mod 13) mod 13
We can substitute our previous result for 7^4 mod 13 into this equation.
7^8 mod 13 = (9 * 9) mod 13 = 81 mod 13 = 3
7^8 mod 13 = 3
We continue in this manner, substituting previous results into our equations.
...after 5 iterations we hit:
7^256 mod 13 = (7^128 * 7^128) mod 13 = (7^128 mod 13 * 7^128 mod 13) mod 13
7^256 mod 13 = (3 * 3) mod 13 = 9 mod 13 = 9
7^256 mod 13 = 9
This has given us a method to calculate A^B mod C quickly provided that B is a power of 2.
However, we also need a method for fast modular exponentiation when B is not a power of 

Let say.. How can we calculate A^B mod C quickly for any B ?
=> Step 1: Divide B into powers of 2 by writing it in binary
Start at the rightmost digit, let k=0 and for each digit:

If the digit is 1, we need a part for 2^k, otherwise we do not
Add 1 to k, and move left to the next digit

=> Step 2: Calculate mod C of the powers of two ≤ B
5^1 mod 19 = 5
5^2 mod 19 = (5^1 * 5^1) mod 19 = (5^1 mod 19 * 5^1 mod 19) mod 19
5^2 mod 19 = (5 * 5) mod 19 = 25 mod 19
5^2 mod 19 = 6
5^4 mod 19 = (5^2 * 5^2) mod 19 = (5^2 mod 19 * 5^2 mod 19) mod 19
5^4 mod 19 = (6 * 6) mod 19 = 36 mod 19
5^4 mod 19 = 17
5^8 mod 19 = (5^4 * 5^4) mod 19 = (5^4 mod 19 * 5^4 mod 19) mod 19
5^8 mod 19 = (17 * 17) mod 19 = 289 mod 19
5^8 mod 19 = 4
5^16 mod 19 = (5^8 * 5^8) mod 19 = (5^8 mod 19 * 5^8 mod 19) mod 19
5^16 mod 19 = (4 * 4) mod 19 = 16 mod 19
5^16 mod 19 = 16
5^32 mod 19 = (5^16 * 5^16) mod 19 = (5^16 mod 19 * 5^16 mod 19) mod 19
5^32 mod 19 = (16 * 16) mod 19 = 256 mod 19
5^32 mod 19 = 9
5^64 mod 19 = (5^32 * 5^32) mod 19 = (5^32 mod 19 * 5^32 mod 19) mod 19
5^64 mod 19 = (9 * 9) mod 19 = 81 mod 19
5^64 mod 19 = 5

=> Step 3: Use modular multiplication properties to combine the calculated mod C values
5^117 mod 19 = ( 5^1 * 5^4 * 5^16 * 5^32 * 5^64) mod 19
5^117 mod 19 = ( 5^1 mod 19 * 5^4 mod 19 * 5^16 mod 19 * 5^32 mod 19 * 5^64 mod 19) mod 19
5^117 mod 19 = ( 5 * 17 * 16 * 9 * 5 ) mod 19
5^117 mod 19 = 61200 mod 19 = 1
5^117 mod 19 = 1

Notes:
More optimization techniques exist, but are outside the scope of this snippet. It should be noted that when we perform modular exponentiation in cryptography, it is not unusual to use exponents for B > 1000 bits.

Objective-C

NSString *plainString = @"foo";
Encoding

NSData *plainData = [plainString dataUsingEncoding:NSUTF8StringEncoding];
NSString *base64String = [plainData base64EncodedStringWithOptions:0];
NSLog(@"%@", base64String); // Zm9v
Decoding

NSData *decodedData = [[NSData alloc] initWithBase64EncodedString:base64String options:0];
NSString *decodedString = [[NSString alloc] initWithData:decodedData encoding:NSUTF8StringEncoding];
NSLog(@"%@", decodedString); // foo 
Swift

let plainString = "foo";
Encoding

let plainData = (plainString as NSString).dataUsingEncoding(NSUTF8StringEncoding)
let base64String = plainData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions.fromRaw(0)!)
println(base64String) // Zm9v
Decoding

let decodedData = NSData(base64EncodedString: base64String, options: NSDataBase64DecodingOptions.fromRaw(0)!)
let decodedString = NSString(data: decodedData, encoding: NSUTF8StringEncoding)    
println(decodedString); // foo 

__attribute((deprecated("Use xxx: instead")))

examples:

@interface MyClass : NSObject
  - (void)myOldMethod:(id)param __attribute__((deprecated));
@end

__attribute__((deprecated))
@interface MyOldClass : NSObject
@end

__attribute__((deprecated))
void myOldFunction(...) {
}

/* 
I discovered the following code that is working well for me:
 */
struct AtomicBoolean {
    private var semaphore = DispatchSemaphore(value: 1)
    private var b: Bool
    var val: Bool  {
        get {
            semaphore.wait()
            let tmp = b
            semaphore.signal()
            return tmp
        }
        set {
            semaphore.wait()
            b = newValue
            semaphore.signal()
        }
    }
    init(_ initialState: Bool) {
        b = initialState
    }
}


/* 
It sure is small and efficient! DispatchSemaphores are also efficient, only going into kernel space if there is contention (reference Concurrency Programming Guide).
 */
var foo = AtomicBoolean(false)
foo.var = true
if foo.var == true {
    print("See!")
}


/* 

 */

NSLog(@"%@", error.localizedDescription) -> "Password should have at least 5 signs"

- (NSDictionary *)validationErrorMessagesByPropertyKey {
    return @{@"password" : 
    		    @{MSGTooShort : @"Password should have at least 5 signs."}
     };
}