TextViewHighlighter

TextViewHighlighter.m

// SO [UITextView - Highlight text with NSBackgroundColor - exclude line breaks](http://stackoverflow.com/questions/26558396/uitextview-text-highlighting-when-the-text-is-centered)

// Source
// TextViewHighlighter.h

#import <Foundation/Foundation.h>
@import UIKit;

@interface TextViewHighlighter : NSObject

- (instancetype)initWithTextView:(UITextView *)textView
                            text:(NSString *)text
                       textColor:(UIColor *)textColor
                highlightedColor:(UIColor *)highlightedColor;

@property (nonatomic, assign) BOOL highlighted;

@end


// TextViewHighlighter.m

#import "TextViewHighlighter.h"

static NSString *const kLinebreakChar = @"\n";

@interface TextViewHighlighter ()

@property (nonatomic, strong) UITextView *textView;
@property (nonatomic, strong) UIColor *textColor;
@property (nonatomic, strong) UIColor *highlightedColor;
@property (nonatomic, copy) NSString *text;

@property (nonatomic, strong) NSAttributedString *highlightedAttributedString;
@property (nonatomic, strong) NSAttributedString *unhighlightedAttributedString;

@end

@implementation TextViewHighlighter

- (instancetype)initWithTextView:(UITextView *)textView
                            text:(NSString *)text
                       textColor:(UIColor *)textColor
                highlightedColor:(UIColor *)highlightedColor {
    self = [super init];
    if (self) {
        _textView = textView;
        _text = text;
        _textColor = textColor;
        _highlightedColor = highlightedColor;

        [self setup];
    }

    return self;
}

- (void)setup {
    NSArray *rangeValues = [self rangeValuesOfLinebreaksInText:self.text];

    // Highlight
    NSMutableAttributedString *highlighedAttributedString = [[NSMutableAttributedString alloc] initWithString:self.text];
    [highlighedAttributedString addAttributes:@{NSForegroundColorAttributeName: self.textColor,
                                                NSBackgroundColorAttributeName: self.highlightedColor
                                                }
                                        range:NSMakeRange(0, self.text.length)];

    for (NSValue *rangeValue in rangeValues) {
        NSRange range = [rangeValue rangeValue];
        [highlighedAttributedString addAttributes:@{NSBackgroundColorAttributeName: [UIColor clearColor],
                                                    }
                                            range:range];
    }

    self.highlightedAttributedString = highlighedAttributedString;

    // Unhighlight
    self.unhighlightedAttributedString = [[NSAttributedString alloc]
                                          initWithString:self.text
                                          attributes:@{NSForegroundColorAttributeName: self.textColor
                                                       }];
}

- (void)setHighlighted:(BOOL)highlighted {
    _highlighted = highlighted;

    self.textView.attributedText = highlighted ? self.highlightedAttributedString : self.unhighlightedAttributedString;
}

#pragma mark - Helper
- (NSArray *)rangeValuesOfLinebreaksInText:(NSString *)text {
    return [self rangeValuesOfCharacter:kLinebreakChar inText:text];
}

- (NSArray *)rangeValuesOfCharacter:(NSString *)character inText:(NSString *)text {
    NSMutableArray *array = [NSMutableArray array];

    NSRange searchRange = NSMakeRange(0, text.length);
    NSRange foundRange;
    while (searchRange.location < text.length) {
        searchRange.length = text.length-searchRange.location;
        foundRange = [text rangeOfString:character options:0 range:searchRange];
        if (foundRange.location != NSNotFound) {
            [array addObject:[NSValue valueWithRange:foundRange]];
            searchRange.location = foundRange.location+foundRange.length;
        } else {
            break;
        }
    }

    return array;
}

@end


// Usage
@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    NSString *text = @"123\n456abc\n789";
    self.highlighter = [[TextViewHighlighter alloc] initWithTextView:self.textView
                                                                text:text
                                                           textColor:[UIColor blueColor]
                                                    highlightedColor:[UIColor blueColor]];
    self.highlighter.highlighted = NO;
}

- (IBAction)touched:(id)sender
{
    self.highlighter.highlighted = !self.highlighter.highlighted;
}