使用给定字符串查找具有恒定宽度和高度的UITextView中适合的字符数？

In my application I need to set Read more into the text view if text input is large.so my approach is to find the range of string that would fit in the text view and append See More to it.Is there any way to achieve it in Swift.The requirement is to emulate the read more option to show the complete text in detailed view on tap like facebook.In my application I need to set Read more into