Iphone emoticons such as the Line app

I am trying to create a chat interface, for example Line app, where you can write emoticons. I tried several different methods:

• UIWebView for cell: I think how they do it, but don’t know how they cache information, so fast.
• UITextView: compute the positions of emoticon codes, and then add images to the text view. The fact is that when you select text, you cannot see emoticons, just text.

Any suggestions for an effective methodology?