我目前在UITextField上有以下扩展来计算给定字符串的边界矩形。funcwidthHeight(font:UIFont)->CGRect{letconstraintRect=CGSize(width:200,height:1000)letboundingBox=self.boundingRect(with:constraintRect,options:.usesLineFragmentOrigin,attributes:[NSFontAttributeName:font],context:nil)returnboundingBox}constraintRect的宽度是我希望框允许