HorizontalScrollView: auto-scroll to end when new Views are added?

Use the View method smoothScrollTo

postDelayed(new Runnable() {
    public void run() {
       scrollView.smoothScrollTo(newView.getLeft(), newView.getTop());
 }
 }, 100L);

You need to put in a runnable so you give time to the layout process to position the new View

I agree with @monxalo and @granko87 that the better approach is with a listener instead of making an assumption that the layout will be complete if we let some arbitrary amount of time pass.

In case, like me, you don't need to use a custom HorizontalScrollView subclass you can just add an OnLayoutChangeListener to keep things simple:

mTagsScroller.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
    @Override
    public void onLayoutChange(View view, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
        mTagsScroller.removeOnLayoutChangeListener(this);
        mTagsScroller.fullScroll(View.FOCUS_RIGHT);
    }
});

I think there's a timing issue. Layout isn't done when a view is added. It is requested and done a short time later. When you call fullScroll immediately after adding the view, the width of the linearlayout hasn't had a chance to expand.

Try replacing:

s.fullScroll(HorizontalScrollView.FOCUS_RIGHT);

with:

s.postDelayed(new Runnable() {
    public void run() {
        s.fullScroll(HorizontalScrollView.FOCUS_RIGHT);
    }
}, 100L);

The short delay should give the system enough time to settle.

P.S. It might be sufficient to simply delay the scrolling until after the current iteration of the UI loop. I have not tested this theory, but if it's right, it would be sufficient to do the following:

s.post(new Runnable() {
    public void run() {
        s.fullScroll(HorizontalScrollView.FOCUS_RIGHT);
    }
});

I like this better because introducing an arbitrary delay seems hacky to me (even though it was my suggestion).

Just another sugestion, since this question helped me a lot :).

You can put a listener when the view has finished its layout phase, and right after do the fullScroll althought you'll need to extend the class for that.

I only did this because i wanted to scroll to a section right after onCreate() to avoid that flickering from starting point to scroll point.

Something like:

public class PagerView extends HorizontalScrollView {

    private OnLayoutListener mListener;
    ///...
    private interface OnLayoutListener {
        void onLayout();
    }

    public void fullScrollOnLayout(final int direction) {
        mListener = new OnLayoutListener() {            
            @Override
            public void onLayout() {
                 fullScroll(direction)
                 mListener = null;
            }
        };
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        if(mListener != null)
             mListener.onLayout();
    }
}