PINCodeField

PINCodeView.h

@interface PINCodeView : UIView

- (instancetype)initWithNumberOfDigits:(NSUInteger)digits
                          keyboardType:(UIKeyboardType)keyboardType
                autocapitalizationType:(UITextAutocapitalizationType)autocapitalizationType;
@property (nonatomic, copy) NSString *code;

- (void)becameFirstResponder;

@end

PINCodeView.m

#import "PINCodeView.h"
#import "PINTextField.h"

@interface PINCodeView() <PINTextFieldDelegate>

@property (nonatomic, copy) NSArray<PINTextField *> *textFields;

@end

@implementation PINCodeView

@synthesize code = _code;

- (instancetype)initWithNumberOfDigits:(NSUInteger)digits
                          keyboardType:(UIKeyboardType)keyboardType
                autocapitalizationType:(UITextAutocapitalizationType)autocapitalizationType {
    self = [super initWithFrame:CGRectZero];
    if (self) {
        _code = @"";
        NSMutableArray *array = [NSMutableArray new];
        for(NSUInteger i = 0; i < digits; i++) {
            PINTextField *textField = [PINTextField new];
            textField.keyboardType = keyboardType;
            textField.autocapitalizationType = autocapitalizationType;
            textField.keyboardAppearance = UIKeyboardAppearanceDark;
            textField.delegate = self;
            [array addObject:textField];
            [self addSubview:textField];
        }
        self.textFields = array;
    }
    return self;
}

- (void)layoutSubviews {
    [super layoutSubviews];
    NSUInteger count = self.textFields.count;
    NSUInteger spaces = count - 1;
    
    CGFloat totalWidth = self.frame.size.width;
    CGFloat totalHeight = self.frame.size.height;
    
    CGFloat viewWidth = totalWidth / (count + spaces * 0.25);
    CGFloat spaceWidth = (totalWidth - (count * viewWidth)) / spaces;
    
    [self.textFields eachWithIndex:^(PINTextField *field, NSUInteger index) {
        field.frame = CGRectMake(index * (viewWidth + spaceWidth), 0, viewWidth, totalHeight);
    }];
}

- (void)becameFirstResponder {
    self.code = [self.code substringToIndex:0];
    [self.textFields[0] becomeFirstResponder];
}

#pragma mark - UITextFieldDelegate

- (void)textFieldDidDelete:(PINTextField *)textField {
    NSUInteger index = [self.textFields indexOfObject:textField];
    if (index > 0) {
        if (index <= self.code.length) {
            [self.code substringToIndex:index - 1];
        }
        [self.textFields[index - 1] becomeFirstResponder];
    }
}

- (void)textField:(PINTextField *)textField didInsert:(NSString *)text {
    NSUInteger index = [self.textFields indexOfObject:textField];
    if (index < self.code.length) {
        self.code = [[self.code substringToIndex:index] stringByAppendingString:text];
    }
    else {
        self.code = [self.code stringByAppendingString:text];
    }
    if (index < self.textFields.count - 1) {
        [self.textFields[index + 1] becomeFirstResponder];
    }
    else {
        [textField resignFirstResponder];
    }
}

- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField {
    NSUInteger index = [self.textFields indexOfObject:(PINTextField *)textField];
    if (index > self.code.length) {
        @weakify(self);
        dispatch_async(dispatch_get_main_queue(), ^{
            @strongify(self);
            if (self.code.length < self.textFields.count) {
                [self.textFields[self.code.length] becomeFirstResponder];
            }
        });
        return NO;
    } else if (index != self.code.length) {
        self.code = [self.code substringToIndex:index];
    }
    return YES;
}

- (void)textFieldDidBeginEditing:(UITextField *)textField {
    textField.text = @"";
    _code = [self collectCode];
}

- (void)setCode:(NSString *)code {
    _code = code;
    [self propagateCode:code];
}

- (NSString *)collectCode {
    return [[self.textFields.rac_sequence map:^NSString *(PINTextField *textField) {
        return textField.text ?: @"";
    }] foldLeftWithStart:@"" reduce:^NSString *(NSString *accumulator, NSString *value) {
        return [accumulator stringByAppendingString:value];
    }];
}

- (void)propagateCode:(NSString *)code {
    NSMutableArray *placeholderStrings = [[self.textFields map:^id(id _) {
        return @"";
    }] mutableCopy];
    [placeholderStrings insertObjects:code.rac_sequence.array
                            atIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, code.length)]];
    [placeholderStrings removeObjectsInRange:NSMakeRange(self.textFields.count,
                                                         placeholderStrings.count - self.textFields.count)];
    NSArray *tuples = [[placeholderStrings.rac_sequence zipWith:self.textFields.rac_sequence] array];
    [tuples each:^(RACTuple *tuple) {
        RACTupleUnpack(NSString *text, PINTextField *textField) = tuple;
        textField.text = text;
    }];
}

@end

PINTextField.h

@class PINTextField;

@protocol PINTextFieldDelegate <UITextFieldDelegate>

- (void)textFieldDidDelete:(PINTextField *)textField;
- (void)textField:(PINTextField *)textField didInsert:(NSString *)text;

@end

@interface PINTextField : UITextField

@property (nonatomic, weak) id<PINTextFieldDelegate> delegate;

@end

PINTextField.m

#import "PINTextField.h"
#import "UIColor+Additions.h"
#import "UIFont+Additions.h"

@implementation PINTextField

@dynamic delegate;

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.autocorrectionType = UITextAutocorrectionTypeNo;
        self.tintColor = UIColor.nl_tintColor;
        self.font = [UIFont systemFontOfSize:24 weight:UIFontWeightMedium];
        self.textColor = UIColor.nl_titleColor;
        self.textAlignment = NSTextAlignmentCenter;
        self.layer.cornerRadius = 2;
        self.backgroundColor = [UIColor.nl_highlightedBackgroundColor colorWithAlphaComponent:0.8];
        self.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
        self.textAlignment = NSTextAlignmentCenter;

        NSDictionary *attributes = @{
                                     NSForegroundColorAttributeName: [UIColor.nl_titleColor colorWithAlphaComponent:0.4],
                                     NSFontAttributeName: [UIFont systemFontOfSize:24 weight:UIFontWeightMedium]
                                     };
        self.attributedPlaceholder = [[NSAttributedString alloc] initWithString:@"*" attributes:attributes];
        if ([[UIDevice currentDevice].systemVersion floatValue] >= 9.0) {
            [self addTarget:self
                     action:@selector(editingChanged:)
           forControlEvents:UIControlEventEditingChanged];
        }
    }
    return self;
}

- (void)editingChanged:(PINTextField *)sender {
    [self insertText:sender.text];
}

- (void)deleteBackward {
    [self.delegate textFieldDidDelete:self];
}

- (void)insertText:(NSString *)text {
    [self.delegate textField:self didInsert:(NSString *)text];
}

- (void)select:(id)sender {} // do nothing
- (void)selectAll:(id)sender {} // do nothing
- (void)paste:(id)sender {} // do nothing
- (BOOL)canPerformAction:(SEL)action withSender:(id)sender { return NO; } // no popup menu actions

- (BOOL)becomeFirstResponder {
    self.selectedTextRange = [self textRangeFromPosition:self.endOfDocument toPosition:self.endOfDocument];
    return [super becomeFirstResponder];
}

@end