how to get current visible substring from long animated-moving string

In a long animated-moving string from right to left, I want to get actually visible substring. Is it possible to get it in an animation process?

I must keep two features of the banner:

1. smooth moving
2. get substring (few characters) in some point on the screen

It is long string in one line.

I use this animation:

[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:10.0];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];

...

[UIView commitAnimations];

I tried with:

CGPoint currentPosition = [[self.a开发者_开发问答utoScrollText.layer presentationLayer] position];

but unsuccessfully...

If your text is in a standard width font, like Courier, you could do this by relating the position of your UITextView, the width of your characters, and the LHS and RHS of your viewport.

Another possibility is to use a heuristic. I guess you are doing a number (i) of different things depending on which string is "visible" when the user clicks a button. Precisely which of these things ultimately depends on the origin (x position) of your text string. Instead of working this out programatically, work it out yourself (through observation/trial and error) and select between the i different options based on the ranges of x that you determine.