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...

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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.

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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.