Scroll ListView from bottom to top

Question

Have a ListView and when the activity starts I want it to scroll from the bottom to the top. I can get this working by setting myListView.setStackFromBottom(true) in onCreate so the list is at the bottom when the activity loads.

Then I override onWindowFocusChanged and use smoothScrollToPosition(0) which will scroll the list to the top. However, I need the scroll speed to gradually slow down as it comes to the top, similar to what a fling looks like. Is there any way to do this with an animation or another way?

Thanks.

Answer 1

You can write your own scroller by using CountDownTimer.

import android.content.Context;
import android.os.CountDownTimer;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.animation.AnticipateOvershootInterpolator;
import android.view.animation.Interpolator;
import android.widget.ScrollView;

public class SmoothScrollView extends ScrollView {

    private static final long SCROLL_DURATION = 1500; //milliseconds
    //interpolator for scroller
    private static final Interpolator INTERPOLATOR = new AnticipateOvershootInterpolator(1);

    private SmoothScroller smoothScroller;


    public SmoothScrollView(Context context) {
        this(context, null, 0);
    }


    public SmoothScrollView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }


    public SmoothScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        setSmoothScrollingEnabled(true);
    }


    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (smoothScroller != null)//we are scrolling
            return true;
        else return super.onTouchEvent(ev);
    }

    @Override
    public boolean executeKeyEvent(KeyEvent ev) {
        if (smoothScroller != null)//we are scrolling
            return true;
        else return super.executeKeyEvent(ev);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        if (smoothScroller != null)//we are scrolling
            return true;
        else return super.onInterceptTouchEvent(ev);
    }

    public void smoothScrollTo(int scrollX, int scrollY) {
        if (smoothScroller != null) {
            smoothScroller.cancel();
        }
        int deltaY = scrollY - getScrollY();
    int deltaX = scrollX - getScrollX();
        smoothScroller = new SmoothScroller(SCROLL_DURATION, getScrollX(), getScrollY(), deltaX, deltaY);
        smoothScroller.start();
    }

    private class SmoothScroller extends CountDownTimer {

        private int fromX;
        private int fromY;
        private int deltaX;
        private int deltaY;
        private float scrollTime;

        public SmoothScroller(long scrollTime, int fromX, int fromY, int deltaX, int deltaY) {
            super(scrollTime, 1);
            this.scrollTime = scrollTime;
            this.fromX = fromX;
            this.fromY = fromY;
            this.deltaX = deltaX;
            this.deltaY = deltaY;
        }

        @Override
        public void onTick(long millisUntilFinished) {
                float delta = (scrollTime - millisUntilFinished) / scrollTime;
                delta = INTERPOLATOR.getInterpolation(delta);
                int x = fromX + ((int) (delta * deltaX));
                int y = fromY + ((int) (delta * deltaY));
                smoothScrollTo(x, y);
        }

        @Override
        public void onFinish() {
                float delta = 1f;
                int x = fromX + ((int) (delta * deltaX));
                int y = fromY + ((int) (delta * deltaY));
                smoothScroller = null;
                scrollTo(x, y);
        }
    }
}

This is what I use. Just change the INTERPOLATOR and SCROLL_DURATION based on your needs and call smoothScrollTo instead scrollTo.

I am pretty sure changing ScrollView to ListView won`t cause any problems.