ios – 突出显示UILabel中的文本

我正在尝试设置背景颜色/突出显示在UILabel内的文本.问题在于,还会突出显示添加到UILabel中以保持文本居中的换行符和空格.

注意UILabel最后一行之前的间距突出显示.此外,任何新行的开始和结束也突出显示.

我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,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;
}

我想实现的输出是只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,所以硬编码解决方案不是一个选择.

解决方法

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

看来,你不能只是问UILabel断线的地方,但是你可以检查一个NSString的大小,当你添加到一个标签.
使用这些信息,您可以逐个增加每个角色,不断检查高度,当高度变化时,您就知道有新行.

我举了一个例子,把Label的字符串和它分隔成UILabel中出现的各个行.一旦我有了每一行,我只是在每一行而不是整个字符串设置背景颜色.这样就可以消除背景颜色,也可以在换行符上设置背景颜色.

可能有更好的解决方案,这可能是为了更好的性能而被优化,但它是一个起点,它似乎起作用.

- (void)createSomeLabel {
    // Create and position my label
    UILabel *someLabel = [[UILabel alloc] initWithFrame:CGRectMake(0,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;
}