UITextView的caretRect换行后minX与maxX返回无穷大问题求助

问题原因 #

UITextView输入换行后，文本布局可能尚未完成，此时调用caretRect(for:)会返回CGRect.infinite，直接访问其minX就会触发崩溃。

解决方案 #

• 防御性判断，跳过无效Rect
  在赋值前先检查Rect是否有效，避免异常值引发崩溃：

  if let cursorPosition = messageTextView.selectedTextRange?.start {
      let caretPositionRect = messageTextView.caretRect(for: cursorPosition)
      guard !caretPositionRect.isInfinite else { return }
      leadingAnchor.constant = caretPositionRect.minX
  }
  

• 通过LayoutManager获取准确光标位置
  直接利用UITextView负责文本布局的layoutManager类获取光标对应的glyph位置，结果更可靠：

  if let cursorPosition = messageTextView.selectedTextRange?.start {
      let glyphIndex = messageTextView.layoutManager.glyphIndex(for: cursorPosition, in: messageTextView.textContainer)
      var glyphRect = messageTextView.layoutManager.boundingRect(forGlyphRange: NSRange(location: glyphIndex, length: 0), in: messageTextView.textContainer)
      glyphRect = messageTextView.convert(glyphRect, from: messageTextView.layoutManager.textContainer)
      leadingAnchor.constant = glyphRect.minX
  }
  

• 等待布局完成后再执行代码
  在textViewDidChange中通过DispatchQueue.main.async延迟执行，让UITextView完成文本布局后再获取光标位置：

  func textViewDidChange(_ textView: UITextView) {
      DispatchQueue.main.async {
          if let cursorPosition = textView.selectedTextRange?.start {
              let caretPositionRect = textView.caretRect(for: cursorPosition)
              leadingAnchor.constant = caretPositionRect.minX
          }
      }
  }
  

内容的提问来源于stack exchange，提问作者newest_tfriz