试试这个：

// Get the width you want to fit
let fixedWidth = textView.frame.size.width

// Calculate the biggest size that fits in the given CGSize
let newSize = textView.sizeThatFits(CGSize(width: fixedWidth, height: CGFloat.greatestFiniteMagnitude))

// Set the textView's size to be whatever is bigger: The fitted width or the fixedWidth
textView.frame.size = CGSize(width: max(newSize.width, fixedWidth), height: newSize.height)

// Make the "background_img_view" height match the textView's height
background_img_view.frame.size.height = textView.frame.size.height