核心文本.如何计算属性字符串的边界框? [英] CoreText. How Do I Calculate the Bounding Box of an Attributed String?

问题描述

在 CoreText 中，很容易问:对于给定的矩形，这个属性字符串中有多少适合?".

In CoreText it is easy ask: "for a given rectangle how much of this attributed string will fit?".

CTFrameGetVisibleStringRange(rect).length

将返回字符串中下一个文本运行应该开始的位置.

Will return where in the string the next run of text should begin.

我的问题是:给定一个属性字符串和一个宽度，我需要什么矩形高度才能完全绑定属性字符串?".

My question is: "given an attributed string and a width, what rect height do I need to completely bound the attributed string?".

CoreText 框架是否提供工具来执行此操作?

Does the CoreText framework provide tools to do this?

谢谢，
道格

推荐答案

你需要的是 CTFramesetterSuggestFrameSizeWithConstraints()，你可以这样使用:

What you need is CTFramesetterSuggestFrameSizeWithConstraints(), you can use it like so:

CTFramesetterRef frameSetter = CTFramesetterCreateWithAttributedString((__bridge CFAttributedStringRef)(attributedString)); /*Create your framesetter based in you NSAttrinbutedString*/
CGFloat widthConstraint = 500; // Your width constraint, using 500 as an example
CGSize suggestedSize = CTFramesetterSuggestFrameSizeWithConstraints(
   framesetter, /* Framesetter */
   CFRangeMake(0, text.length), /* String range (entire string) */
   NULL, /* Frame attributes */
   CGSizeMake(widthConstraint, CGFLOAT_MAX), /* Constraints (CGFLOAT_MAX indicates unconstrained) */
   NULL /* Gives the range of string that fits into the constraints, doesn't matter in your situation */
);
CGFloat suggestedHeight = suggestedSize.height;

编辑

//IMPORTANT: Release the framesetter, even with ARC enabled!
CFRelease(frameSetter);

因为 ARC 只发布 Objective-C 对象，而 CoreText 处理 C，很可能您会在这里出现内存泄漏.如果你的 NSAttributedString 很小并且你做了一次，你不应该有任何不好的后果.但是如果你有一个循环来计算，比如说，大/复杂 NSAttributedStrings 的 50 个高度，并且你不释放 CTFramesetterRef，你可以有严重的内存泄漏.查看链接的教程，了解有关内存泄漏和使用仪器调试的更多信息.

As ARC releases only Objective-C objects, and CoreText deals with C, very likely you can have a memory leak here. If your NSAttributedString is small and you do it once, you shouldn't have any bad consequences. But in a case you have a loop to calculate, let's say, 50 heights of big/complex NSAttributedStrings, and you don't release the CTFramesetterRef, you can have serious memory leaks. Check the tutorial linked for more information on memory leaks and debugging with instruments.

所以这个问题的解决方法是添加CFRelease(frameSetter);

So the solution for this problem is to add CFRelease(frameSetter);

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