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

Question

I have a HorizontalScrollView containing a LinearLayout. On screen I have a Button that will add new Views to the LinearLayout at runtime, and I\'d like the scroll view to

Answer 1

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);
    }
});

Answer 2

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

Answer 3

I think the best approach is the one posted by monxalo because you can not know how much time will it take until the layout is done. I tried it and it works perfectly. The only difference is, that I added only one row to my custom horizontal scroll view:

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    super.onLayout(changed, l, t, r, b);
    this.fullScroll(HorizontalScrollView.FOCUS_RIGHT);
}

Answer 4

This is what I did.

//Observe for a layout change    
ViewTreeObserver viewTreeObserver = yourLayout.getViewTreeObserver();
   if (viewTreeObserver.isAlive()) {
     viewTreeObserver.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                yourHorizontalScrollView.fullScroll(HorizontalScrollView.FOCUS_RIGHT);
            }
     });
   }

Answer 5

The child View may not be immediately added in a ViewGroup. So it is required to post a Runnable which will run after other pending tasks are completed.

So after adding View, use:

horizontalScrollView.post(new Runnable() {
    @Override
    public void run() {
        horizontalScrollView.fullScroll(View.FOCUS_RIGHT);
    }
});

Answer 6

This is my way for 3 ImageViews in kotlin:

var p1 = true; var p2 = false; var p3 = false
val x = -55
val handler = Handler()
handler.postDelayed(object : Runnable {
    override fun run() {

        if (p1){
            mainView.picsScrollViewID.smoothScrollTo(mainView.bigPic1ID.x.toInt() + x, 0)
            p1 = false
            p2 = true
            p3 = false
        }
        else if(p2){
            mainView.picsScrollViewID.smoothScrollTo(mainView.bigPic2ID.x.toInt() + x, 0)
            p1 = false
            p2 = false
            p3 = true
        }
        else if(p3){
            mainView.picsScrollViewID.smoothScrollTo(mainView.bigPic3ID.x.toInt() + x, 0)
            p1 = true
            p2 = false
            p3 = false
        }
        handler.postDelayed(this, 2000)
    }
}, 1400)