NSParagraphStyle行间距被忽略

问题描述

一个失败的简单测试：用一个子视图（UITextView）创建一个新项目并将以下内容放入：

A simple test that is failed: Make a new project with just one subview (UITextView) and put the following in:

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
    paragraphStyle.lineHeightMultiple = 50.f;
    paragraphStyle.lineSpacing = 100.f;
    paragraphStyle.minimumLineHeight = 200.f;
    paragraphStyle.maximumLineHeight = 500.f;

    UIFont *font = [UIFont fontWithName:@"AmericanTypewriter" size:24.f];

    self.textView.attributedText = [[NSAttributedString alloc] initWithString:
    @"This is a test.\n Will I pass?" attributes:
    @{NSParagraphStyleAttributeName : paragraphStyle, NSFontAttributeName : font}];
}

行间距与属性不存在时相同。有什么能成功地运作吗？我添加了荒谬的数字只是为了表明它不会改变......

Line spacing is the same as if the attribute were not there. Has anything got this to work successfully? I put in ridiculous numbers just to show that it won't change...

推荐答案

这是NSHTMLWriter中的一个错误，它是UITextView用于将attributedText转换为HTML的私有类。在内部，它通过UIWebDocumentView显示此HTML。在我的文章中阅读更多关于UITextView内部工作原理的内容：

This is a bug in NSHTMLWriter which is the private class which UITextView uses to convert attributedText into HTML. Internally it displays this HTML via a UIWebDocumentView. Read more on the inner workings of UITextView in my writeup here: http://www.cocoanetics.com/2012/12/uitextview-caught-with-trousers-down/

问题来自于字体CSS中容易遗漏的特色速记。如果您使用字体速记指定像素大小，则会将字体大小和行高设置为BOTH。由于NSHTMLWriter将字体放在行高后，这会导致行高被字体大小抵消。

The problem comes from an easy to miss speciality in the font CSS shorthand. If you specify a pixel size with the font shorthand then this sets BOTH the font-size as well as the line-height. Since NSHTMLWriter puts the font AFTER the line-height this causes the line-height to be cancelled out by the font size.

请参阅此处查看我的雷达，其中包括完整分析错误：

See here for my Radar which includes the full analysis of the bug: http://www.cocoanetics.com/2012/12/radar-uitextview-ignores-minimummaximum-line-height-in-attributed-string/

我建议你提交bug报告并提及我的雷达＃12863734。

I suggest you file a bug report as well and mention my Radar #12863734.

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