How to stop scroll in progress in NestedScrollView?

Question

I have a button to automatically returns to top position into a NestedScrollView. When the scroll is not in progress, it works like a charm, otherwise if the current scrolling is in progress yet, the scroll goes to top but directly scroll a lit bit down just after...

I wrote this method:

private void scrollToTop() {
        mScrollView.stopNestedScroll();
        mScrollView.postDelayed(new Runnable() {
            @Override
            public void run() {
                mScrollView.scrollTo(0, 0);
            }
        }, 50);
    }

Have you got some ideas guys to stop the current scroll and go to top immediately?

Thank you very much

Did you find a solution? – Keivan Esbati Apr 25 '18 at 05:01 — Keivan Esbati, Apr 25 '18 at 05:01

score 1 · Accepted Answer · edited Oct 21 '21 at 18:16

The correct way would be intercepting user's touch when you scrolling pragmatically. That would require you to extend ScrollView overriding scrollTo and onInterceptTouchEvent methods and disable user touch while list is scrolling, returning touch after scroll is complete.

So the sequence would be like this:

Call scrollTo to scroll to specific position
Enable a flag to disable touch events and begin scrolling
When scroll is finished and state changed to idle disable flag

P.S: I can provide code example but it appears you have more expertise than me in writing codes. Cheers!

Here a code snippet:

import android.content.Context;
import android.support.v4.widget.NestedScrollView;
import android.util.AttributeSet;
import android.view.MotionEvent;

public class MyScrollView extends NestedScrollView {

    public static final int MAX_SCROLL_FACTOR = 1;
    boolean isAutoScrolling;

    public MyScrollView(Context context) {
        super(context);
    }

    public MyScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public void scrollTo(int x, int y) {
        isAutoScrolling = true;
        super.scrollTo(x, y);
    }


    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        if (isAutoScrolling)
            return super.onInterceptTouchEvent(event);

        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (isAutoScrolling)
            return super.onTouchEvent(event);


        return false;
    }

    @Override
    protected void onScrollChanged(int x, int y, int oldX, int oldY) {
        super.onScrollChanged(x, y, oldX, oldY);
        if (isAutoScrolling) {
            if (Math.abs(y - oldY) < MAX_SCROLL_FACTOR  || y >= getMeasuredHeight() || y == 0
                    || Math.abs(x - oldX) < MAX_SCROLL_FACTOR || x >= getMeasuredWidth() || x == 0) {
                isAutoScrolling = false;
            }
        }
    }
}

Hi Keivan! Thanks for your reply, but I'm not sure about your solution. Did you test it in the same context like my problem? — anthony, Apr 24 '18 at 06:09
Yes, I tested it with ViewPager. My scenario was animating ViewPager transition and I encountered the exact same problem.. I can provide code snippet if it helps. Though it is just overriding few method with a simple boolean flag — Keivan Esbati, Apr 24 '18 at 06:13
Added code snippet, right now I'm searching for a way to detect when scroll is ended. though it can done via looper but i think there are better ways to do so. — Keivan Esbati, Apr 24 '18 at 06:46
@anthony hmm finally found a decent way to detect scroll ending ^^ — Keivan Esbati, Apr 24 '18 at 06:57

score 0 · Answer 2 · answered Feb 23 '23 at 08:07

A tricky solution

private void scrollToTop() {
    mScrollView.stopNestedScroll();
    mScrollTop = true
    mScrollView.postDelayed(new Runnable() {
        @Override
        public void run() {
            mScrollView.scrollTo(0, 0);
        }
    }, 50);
}

This method stays still, dectect scrolling and scroll is reach top(kotlin code)

 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        scrollView.setOnScrollChangeListener { scrollView, scorllX, scrollY, oldScrollX, oldScrollY ->
            scrollTop()
        }
    } else {
        scrollView.viewTreeObserver.addOnScrollChangedListener {
            scrollTop()
        }
    }
    private fun scrollTop() {
        if(mScrollTop) {
            if(scrollView.scrollY == 0){
               mScrollTop = false
            } else {
               scrollView.fullScroll(View.FOCUS_UP)
            }
        }
    }

How to stop scroll in progress in NestedScrollView?

2 Answers2

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