如何创建一个自动包装文本行的UITextView？

I am creating an app that creates a UITextView programmatically. The problem is, when the user types in text or the app sets the text, the words spread across one line and off the screen, rather than wrapping to the next line. When I create a UITextView with interface builder, the text wraps automatically, but not when it is created programmatically.I am creating an app that creates a UITextView