如何获取 CATextLayer 的环绕计数以计算高度 [英] How to get CATextLayer’s wrapping count in order to calculate height

问题描述

我正在将文本增量添加到 UIScrollView 中的包装 CATextLayer.每次添加文本时，都需要给textLayer和scrollView的contentSize添加高度，并调整scrollView的contentOffset.

I am adding text incrementally to a wrapping CATextLayer in a UIScrollView. Each time I add text, I need to add height to the textLayer and to the scrollView’s contentSize, and adjust the scrollView’s contentOffset.

(用户应该能够使用 scrollView 查看以前的文本，但是当添加新文本时，我想以编程方式向下滚动到它.)

(The user should be able to use the scrollView to review previous text, but when new text is added, I want to scroll down to it programmatically.)

UIKit 的 sizeWithFont: 会将整个字符串视为在一行上，因此为了计算高度，我需要乘以行数返回的 size.height，如由 textLayer 的包装产生.

UIKit’s sizeWithFont: will treat the entire string as though it is on one line, so in order to calculate the height, I need to multiple the size.height returned by the number of lines, as produced by the textLayer’s wrapping.

问题是，如果我通过 textLayer 访问字符串，它不会包含任何额外的\n"或\r"字符来解释换行.

Trouble is, if I access the string through the textLayer, it won’t contain any extra ‘\n’ or ‘\r’ characters to account for the wrapping.

当然有某种方法可以获得包装信息吗?也许以某种方式源自超类 CALayer ?否则我会被困在计算自己的换行符中.

Surely there is some way I can get the wrapping info? Perhaps dervied from superclass CALayer somehow? Otherwise I’m stuck calculating my own line breaks.

推荐答案

我假设 CATextLayer 在内部使用 Core Text 进行布局，所以你可以这样做并使用 CTFramesetterSuggestFrameSizeWithConstraints 为具有给定宽度的属性字符串计算适当的高度.

I assume that CATextLayer internally uses Core Text for layout, so you could do the same and use CTFramesetterSuggestFrameSizeWithConstraints to calculate an appropriate height for an attributed string with a given width.

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