Is there a way to programmatically scroll a scroll

Question

I have a very long activity with a scrollview. It is a form with various fields that the user must fill in. I have a checkbox half way down my form, and when the user checks it I want to scroll to a specific part of the view. Is there any way to scroll to an EditText object (or any other view object) programmatically?

Also, I know this is possible using X and Y coords but I want to avoid doing this as the form may changed from user to user.

Answer 1

The answer of Sherif elKhatib can be greatly improved, if you want to scroll the view to the center of the scroll view. This reusable method smooth scrolls the view to the visible center of a HorizontalScrollView.

private final void focusOnView(final HorizontalScrollView scroll, final View view) {
    new Handler().post(new Runnable() {
        @Override
        public void run() {
            int vLeft = view.getLeft();
            int vRight = view.getRight();
            int sWidth = scroll.getWidth();
            scroll.smoothScrollTo(((vLeft + vRight - sWidth) / 2), 0);
        }
    });
}

For a vertical ScrollView change the x and y position of inputs of smoothScroll. And use view.getTop() instead of view.getLeft() and view.getBottom() instead of v.getRight().

:)

Answer 2

The above answers will work fine if the ScrollView is the direct parent of the ChildView. If your ChildView is being wrapped in another ViewGroup in the ScrollView, it will cause unexpected behavior because the View.getTop() get the position relative to its parent. In such case, you need to implement this:

public static void scrollToInvalidInputView(ScrollView scrollView, View view) {
    int vTop = view.getTop();

    while (!(view.getParent() instanceof ScrollView)) {
        view = (View) view.getParent();
        vTop += view.getTop();
    }

    final int scrollPosition = vTop;

    new Handler().post(() -> scrollView.smoothScrollTo(0, scrollPosition));
}

Answer 3

Examining Android source code, you can find that there already is a member function of ScrollView– scrollToChild(View) – that does exactly what is requested. Unfortunatelly, this function is for some obscure reason marked private. Based on that function I've written following function that finds the first ScrollView above the View specified as a parameter and scrolls it so that it becomes visible within the ScrollView:

 private void make_visible(View view)
 {
  int vt = view.getTop();
  int vb = view.getBottom();

  View v = view;

  for(;;)
     {
      ViewParent vp = v.getParent();

      if(vp == null || !(vp instanceof ViewGroup))
         break;

      ViewGroup parent = (ViewGroup)vp;

      if(parent instanceof ScrollView)
        {
         ScrollView sv = (ScrollView)parent;

         // Code based on ScrollView.computeScrollDeltaToGetChildRectOnScreen(Rect rect) (Android v5.1.1):

         int height = sv.getHeight();
         int screenTop = sv.getScrollY();
         int screenBottom = screenTop + height;

         int fadingEdge = sv.getVerticalFadingEdgeLength();

         // leave room for top fading edge as long as rect isn't at very top
         if(vt > 0)
            screenTop += fadingEdge;

         // leave room for bottom fading edge as long as rect isn't at very bottom
         if(vb < sv.getChildAt(0).getHeight())
            screenBottom -= fadingEdge;

         int scrollYDelta = 0;

         if(vb > screenBottom && vt > screenTop) 
           {
            // need to move down to get it in view: move down just enough so
            // that the entire rectangle is in view (or at least the first
            // screen size chunk).

            if(vb-vt > height) // just enough to get screen size chunk on
               scrollYDelta += (vt - screenTop);
            else              // get entire rect at bottom of screen
               scrollYDelta += (vb - screenBottom);

             // make sure we aren't scrolling beyond the end of our content
            int bottom = sv.getChildAt(0).getBottom();
            int distanceToBottom = bottom - screenBottom;
            scrollYDelta = Math.min(scrollYDelta, distanceToBottom);
           }
         else if(vt < screenTop && vb < screenBottom) 
           {
            // need to move up to get it in view: move up just enough so that
            // entire rectangle is in view (or at least the first screen
            // size chunk of it).

            if(vb-vt > height)    // screen size chunk
               scrollYDelta -= (screenBottom - vb);
            else                  // entire rect at top
               scrollYDelta -= (screenTop - vt);

            // make sure we aren't scrolling any further than the top our content
            scrollYDelta = Math.max(scrollYDelta, -sv.getScrollY());
           }

         sv.smoothScrollBy(0, scrollYDelta);
         break;
        }

      // Transform coordinates to parent:
      int dy = parent.getTop()-parent.getScrollY();
      vt += dy;
      vb += dy;

      v = parent;
     }
 }

Answer 4

In my case, that's not EditText, that's googleMap. And it works successfully like this.

    private final void focusCenterOnView(final ScrollView scroll, final View view) {
    new Handler().post(new Runnable() {
        @Override
        public void run() {
            int centreX=(int) (view.getX() + view.getWidth()  / 2);
            int centreY= (int) (view.getY() + view.getHeight() / 2);
            scrollView.smoothScrollBy(centreX, centreY);
        }
    });
}

Answer 5

I made a small utility method based on Answer from WarrenFaith, this code also takes in account if that view is already visible in the scrollview, no need for scroll.

public static void scrollToView(final ScrollView scrollView, final View view) {

    // View needs a focus
    view.requestFocus();

    // Determine if scroll needs to happen
    final Rect scrollBounds = new Rect();
    scrollView.getHitRect(scrollBounds);
    if (!view.getLocalVisibleRect(scrollBounds)) {
        new Handler().post(new Runnable() {
            @Override
            public void run() {
                scrollView.smoothScrollTo(0, view.getBottom());
            }
        });
    } 
}

Answer 6

In my opinion the best way to scroll to a given rectangle is via View.requestRectangleOnScreen(Rect, Boolean). You should call it on a View you want to scroll to and pass a local rectangle you want to be visible on the screen. The second parameter should be false for smooth scrolling and true for immediate scrolling.

final Rect rect = new Rect(0, 0, view.getWidth(), view.getHeight());
view.requestRectangleOnScreen(rect, false);