Scrolling parallel views simultaneously

Question

I have two ScrollView's side by side and by using the code below I can scroll them simultaneously but I still can scroll them each independently throwing off the scroll positions. How can I make each view scroll simultaneously and disable scrolling each view by itself? I apologize if there's any confusion in my question. Any help would be appreciated, thanks.

ScrollView sv1;
ScrollView sv2;
View clickSource;
View touchSource; 

   sv1.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            if(touchSource == null)
                touchSource = v;

            if(v == touchSource) {
                sv2.dispatchTouchEvent(event);
                if(event.getAction() == MotionEvent.ACTION_UP) {
                    clickSource = v;
                    touchSource = null;
                }
            }

            return false;
        }
    });
    sv2.setOnTouchListener(new View.OnTouchListener(){
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            if(touchSource == null)
                touchSource = v;

            if(v == touchSource) {
                sv1.dispatchTouchEvent(event);
                if(event.getAction() == MotionEvent.ACTION_UP) {
                    clickSource = v;
                    touchSource = null;
                }
            }

            return false;
        }
    });

Answer 1

Try this

sv1.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {

    @Override
    public void onScrollChanged() {
        int scrollX = sv1.getScrollX(); // for horizontalScrollView
        int scrollY = sv1.getScrollY(); // for verticalScrollView
        // DO SOMETHING WITH THE SCROLL COORDINATES
        sv2.scrollTo(scrollX, scrollY);
    }
});

Answer 2

Hopefully I understand your question correctly. If you want both ScrollViews to scroll simultaneously then the code below should do the trick (untested):

First create an interface to listen to scroll events:

public interface ScrollChangeListener {

    public void onScrollChanged(View view, int x, int y, int oldx, int oldy);
}

Next, create a custom view so you can listen for scroll changes:

public class ObservableScrollView extends ScrollView {

    private ScrollChangeListener mScrollChangeListener;

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

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

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

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public ObservableScrollView(Context context, AttributeSet attrs, int defStyleAttr,
                                int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    public void setScrollChangeListener(ScrollChangeListener listener) {
        mScrollChangeListener = listener;
    }

    @Override
    protected void onScrollChanged(int x, int y, int oldx, int oldy) {
        if (mScrollChangeListener != null) {
            mScrollChangeListener.onScrollChanged(this, x, y, oldx, oldy);
        }
    }
}

Use your custom view and create a listener for both ScrollViews.

ObservableScrollView mScrollView1;

ObservableScrollView mScrollView2;

...

ScrollChangeListener listener = new ScrollChangeListener() {

    @Override
    public void onScrollChanged(View view, int x, int y, int oldx, int oldy) {
        ScrollView scrollView;
        if (view == mScrollView1) {
            scrollView = mScrollView2;
        } else if (view == mScrollView2) {
            scrollView = mScrollView1;
        } else {
            return;
        }
        scrollView.scrollTo(x, y);
    }
};

...

mScrollView1.setScrollChangeListener(listener);
mScrollView2.setScrollChangeListener(listener);