仅突出显示 UILabel 中的文本

Question

我正在尝试设置背景颜色/仅突出显示 UILabel 中的文本。问题是添加到UILabel 以保持文本居中的换行符和空格也被突出显示。

注意UILabel 中最后一行之前的间距被突出显示。此外，任何新行的开头和结尾也会突出显示。

我正在使用以下代码创建上面的示例：

-(void)createSomeLabel {
    // Create and position my label
    UILabel *someLabel = [[UILabel alloc] initWithFrame:CGRectMake(0,
                                                                   0,
                                                                   self.view.frame.size.width - 40,
                                                                   self.view.frame.size.height - 300)];
    someLabel.center = CGPointMake(self.view.frame.size.width / 2, self.view.frame.size.height / 2);
    someLabel.textAlignment = NSTextAlignmentCenter;
    someLabel.textColor = [UIColor whiteColor];
    someLabel.lineBreakMode = NSLineBreakByWordWrapping;
    someLabel.numberOfLines = 0;
    [self.view addSubview:someLabel];

    // This string will be different lengths all the time
    NSString *someLongString = @"Here is a really long amount of text that is going to wordwrap/line break and I don't want to highlight the spacing. I want to just highlight the words and a single space before/after the word";

    // Create attributed string
    NSMutableAttributedString *someLongStringAttr=[[NSMutableAttributedString alloc] initWithString:someLongString attributes:nil];

    // Apply background color
    [someLongStringAttr addAttribute:NSBackgroundColorAttributeName
                      value:[UIColor colorWithWhite:0 alpha:0.25]
                      range:NSMakeRange(0, someLongStringAttr.length)];

    // Set text of label
    someLabel.attributedText = someLongStringAttr;
}

我想要实现的输出是仅突出显示文本和单词之间的空格（如果只有一个空格）。文本的长度和UILabel 的大小会不断变化，所以很遗憾，硬编码解决方案不是一种选择。

Answer 1

在我看来，换行是问题所在。 我的想法是尝试知道 UILabel 何时会添加换行符，然后从突出显示的字符范围中删除该字符。

您似乎不能只询问 UILabel 换行符将在哪里，但您可以检查将 NSString 添加到标签时的大小。 使用此信息，您可以不断检查每个字符的高度，当高度发生变化时，您知道您有一个新行。

我已经做了一个例子，它采用标签的字符串并将其分成单独的行，这些行将出现在 UILabel 中。一旦我有了每一行，我只需在每一行而不是整个字符串上设置背景颜色。这消除了在换行符处设置的背景颜色。

可能有更好的解决方案，并且这个解决方案可能会进行优化以获得更好的性能，但它只是一个起点，而且似乎可行。

- (void)createSomeLabel {
    // Create and position my label
    UILabel *someLabel = [[UILabel alloc] initWithFrame:CGRectMake(0,
                                                                   0,
                                                                   self.view.frame.size.width - 40,
                                                                   self.view.frame.size.height - 300)];
    someLabel.center = CGPointMake(self.view.frame.size.width / 2, self.view.frame.size.height / 2);
    someLabel.textAlignment = NSTextAlignmentCenter;
    someLabel.textColor = [UIColor whiteColor];
    someLabel.lineBreakMode = NSLineBreakByWordWrapping;
    someLabel.numberOfLines = 0;
    [self.view addSubview:someLabel];

    // This string will be different lengths all the time
    NSString *someLongString = @"Here is a really long amount of text that is going to wordwrap/line break and I don't want to highlight the spacing. I want to just highlight the words and a single space before/after the word";

    // Create attributed string
    NSMutableAttributedString *someLongStringAttr=[[NSMutableAttributedString alloc] initWithString:someLongString attributes:nil];


    // The idea here is to figure out where the UILabel would automatically make a line break and get each line of text separately.
    // Temporarily set the label to be that string so that we can guess where the UILabel naturally puts its line breaks.
    [someLabel setText:someLongString];
    // Get an array of each individual line as the UILabel would present it.
    NSArray *allLines = getLinesForLabel(someLabel);
    [someLabel setText:@""];


    // Loop through each line of text and apply the background color to just the text within that range.
    // This way, no whitespace / line breaks will be highlighted.
    __block int startRange = 0;
    [allLines enumerateObjectsUsingBlock:^(NSString *line, NSUInteger idx, BOOL *stop) {

        // The end range should be the length of the line, minus one for the whitespace.
        // If we are on the final line, there are no more line breaks so we use the whole line length.
        NSUInteger endRange = (idx+1 == allLines.count) ?  line.length : line.length-1;

        // Apply background color
        [someLongStringAttr addAttribute:NSBackgroundColorAttributeName
                                   value:[UIColor colorWithWhite:0 alpha:0.25]
                                   range:NSMakeRange(startRange, endRange)];

        // Update the start range to the next line
        startRange += line.length;
    }];



    // Set text of label
    someLabel.attributedText = someLongStringAttr;
}


#pragma mark - Utility Functions

static NSArray *getLinesForLabel(UILabel *label) {

    // Get the text from the label
    NSString *labelText = label.text;

    // Create an array to hold the lines of text
    NSMutableArray *allLines = [NSMutableArray array];

    while (YES) {

        // Get the length of the current line of text
        int length = getLengthOfTextInFrame(label, labelText) + 1;

        // Add this line of text to the array
        [allLines addObject:[labelText substringToIndex:length]];

        // Adjust the label text
        labelText = [labelText substringFromIndex:length];

        // Check for the final line
        if(labelText.length<length) {
            [allLines addObject:labelText];
            break;
        }
    }

    return [NSArray arrayWithArray:allLines];
}

static int getLengthOfTextInFrame(UILabel *label, NSString *text) {

    // Create a block for getting the bounds of the current peice of text.
    CGRect (^boundingRectForLength)(int) = ^CGRect(int length) {
        NSString *cutText = [text substringToIndex:length];
        CGRect textRect = [cutText boundingRectWithSize:CGSizeMake(label.frame.size.width, CGFLOAT_MAX)
                                                options:NSStringDrawingUsesLineFragmentOrigin
                                             attributes:@{NSFontAttributeName : label.font}
                                                context:nil];
        return textRect;
    };

    // Get the frame of the string for one character
    int length = 1;
    int lastSpace = 1;
    CGRect textRect = boundingRectForLength(length);
    CGFloat oneLineHeight = CGRectGetHeight(textRect);

    // Keep adding one character to the string until the height changes, then you know you have a new line
    while (textRect.size.height <= oneLineHeight)
    {
        // If the next character is white space, save the current length.
        // It could be the end of the line.
        // This will not work for character wrap.
        if ([[text substringWithRange:NSMakeRange (length, 1)] isEqualToString:@" "]) {
            lastSpace = length;
        }

        // Increment length and get the new bounds
        textRect = boundingRectForLength(++length);
    }

    return lastSpace;
}

Answer 2

我也遇到过同样的问题，并找到了更简单的解决方案，而且没有巨大的性能成本。您可以简单地将TTTAttributedLabel 添加到您的项目中。

我的问题演示项目：

#import "TTTAttributedLabel.h"

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    UILabel *label1 = [UILabel new];
    label1.textAlignment = NSTextAlignmentCenter;
    label1.numberOfLines = 0;
    label1.frame = CGRectMake(20, 0, CGRectGetWidth(self.view.frame) - 40, CGRectGetHeight(self.view.frame) / 2.0);
    [self.view addSubview:label1];

    TTTAttributedLabel *label2 = [TTTAttributedLabel new];
    label2.textAlignment = NSTextAlignmentCenter;
    label2.numberOfLines = 0;
    label2.frame = CGRectMake(20, CGRectGetHeight(self.view.frame) / 2.0, CGRectGetWidth(self.view.frame) - 40, CGRectGetHeight(self.view.frame) / 2.0);
    [self.view addSubview:label2];

    NSDictionary *attributes = @{NSBackgroundColorAttributeName:[UIColor blackColor], NSForegroundColorAttributeName:[UIColor whiteColor], NSFontAttributeName:[UIFont systemFontOfSize:32 weight:UIFontWeightBold]};
    NSAttributedString *string = [[NSAttributedString alloc] initWithString:@"Some very long string which can contain newlines and some other stuff" attributes:attributes];
    label1.attributedText = string;
    label2.text = string;
}

@end

Answer 3

从 iOS 10.3 开始，有问题的相同代码现在会产生所需的结果。不确定这是错误还是新功能。

-(void)createSomeLabel {
    // Create and position my label
    UILabel *someLabel = [[UILabel alloc] initWithFrame:CGRectMake(0,
                                                                   0,
                                                                   self.view.frame.size.width - 40.0,
                                                                   self.view.frame.size.height - 300.0)];
    someLabel.center = CGPointMake(self.view.frame.size.width / 2.0, self.view.frame.size.height / 2.0);
    someLabel.textAlignment = NSTextAlignmentCenter;
    someLabel.textColor = [UIColor whiteColor];
    someLabel.lineBreakMode = NSLineBreakByWordWrapping;
    someLabel.numberOfLines = 0;
    [self.view addSubview:someLabel];

    // This string will be different lengths all the time
    NSString *someLongString = @"Here is a really long amount of text that is going to wordwrap/line break and I don't want to highlight the spacing. I want to just highlight the words and a single space before/after the word";

    // Create attributed string
    NSMutableAttributedString *someLongStringAttr = [[NSMutableAttributedString alloc] initWithString:someLongString attributes:nil];

    // Apply background color
    [someLongStringAttr addAttribute:NSBackgroundColorAttributeName
                               value:[UIColor colorWithWhite:0 alpha:0.25]
                               range:NSMakeRange(0, someLongStringAttr.length)];

    // Set text of label
    someLabel.attributedText = someLongStringAttr;
}