UITextView删除原有字符串时，光标会上移并且光标会变高

代码运行效果如图：

import Foundationclass TestVC: UIViewController {override func viewDidLoad() {super.viewDidLoad()let testV = MyCustomTextView(frame: CGRect(x: 0, y: 130, width: SCREEN_WIDTH - 50, height: 170))self.view.addSubview(testV)testV.backgroundColor = .darkGraylet ps = NSMutableParagraphStyle()ps.lineSpacing = 7ps.alignment = .leftlet attr = NSMutableAttributedString(string: "字", attributes: [.font: UIFont.systemFont(ofSize: 20),.foregroundColor: UIColor.blue,.paragraphStyle: ps.copy()])testV.attributedText = attr}
}extension TestVC: UITextViewDelegate {func textViewDidChange(_ textView: UITextView) {let text = textView.text ?? ""let ps = NSMutableParagraphStyle()ps.lineSpacing = 7ps.alignment = .leftlet attr = NSMutableAttributedString(string: text, attributes: [.font: UIFont.systemFont(ofSize: 20),.foregroundColor: UIColor.blue,.paragraphStyle: ps.copy()])textView.attributedText = attr}
}class MyCustomTextView: UITextView {override func caretRect(for position: UITextPosition) -> CGRect {var rect = super.caretRect(for: position)var text = self.text// 计算字符串为空时的textView rect, 避免删完字符串时出现的光标变高和上移问题// 如果自己还要做换行效果, 那么只在self.text.isEmpty时用sizeToFitif self.text.isEmpty {//  用"AAgg"可以算出字符串最大高度, 因为一个往上占据位置, 一个往下占据位置.text = "AAgg"}let label = UILabel()label.font = self.fontlabel.text = textlabel.sizeToFit()rect.size.height = label.heightreturn rect}
}