How to make a Scroll Listener for WebView in Android

Something like:

public class ObservableWebView extends WebView
{
    private OnScrollChangedCallback mOnScrollChangedCallback;

    public ObservableWebView(final Context context)
    {
        super(context);
    }

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

    public ObservableWebView(final Context context, final AttributeSet attrs, final int defStyle)
    {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onScrollChanged(final int l, final int t, final int oldl, final int oldt)
    {
        super.onScrollChanged(l, t, oldl, oldt);
        if(mOnScrollChangedCallback != null) mOnScrollChangedCallback.onScroll(l, t, oldl, oldt);
    }

    public OnScrollChangedCallback getOnScrollChangedCallback()
    {
        return mOnScrollChangedCallback;
    }

    public void setOnScrollChangedCallback(final OnScrollChangedCallback onScrollChangedCallback)
    {
        mOnScrollChangedCallback = onScrollChangedCallback;
    }

    /**
     * Impliment in the activity/fragment/view that you want to listen to the webview
     */
    public static interface OnScrollChangedCallback
    {
        public void onScroll(int l, int t, int oldl, int oldt);
    }
}

Should work, this is untested but this works for almost every other view in Android.

You would implement like:

wv = (ObservableWebView) findViewById(R.id.scorllableWebview);
wv.setOnScrollChangedCallback(new OnScrollChangedCallback(){
    public void onScroll(int l, int t, int oldl, int oldt){
        if(t> oldt){
            //Do stuff
            System.out.println("Swipe UP");
            //Do stuff
        }
        else if(t< oldt){
            System.out.println("Swipe Down");
        }
        Log.d(TAG,"We Scrolled etc...");
    }
});

Since API 23, you won't need to do it anymore, you can just use the new OnScrollChangeListener available on all views, including on the WebView. But as you still need to support older versions, you can still use the suggestion from @Chris.Jenkins. I made some adjustments the proposed class to be 'more compatible' with the new OnScrollChangeListener interface:

public class ObservableWebView extends WebView {
private OnScrollChangeListener onScrollChangeListener;

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

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

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

@Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
    super.onScrollChanged(l, t, oldl, oldt);
    if (onScrollChangeListener != null) {
        onScrollChangeListener.onScrollChange(this, l, t, oldl, oldt);
    }
}

public void setOnScrollChangeListener(OnScrollChangeListener onScrollChangeListener) {
    this.onScrollChangeListener = onScrollChangeListener;
}

public OnScrollChangeListener getOnScrollChangeListener() {
    return onScrollChangeListener;
}

public interface OnScrollChangeListener {
    /**
     * Called when the scroll position of a view changes.
     *
     * @param v          The view whose scroll position has changed.
     * @param scrollX    Current horizontal scroll origin.
     * @param scrollY    Current vertical scroll origin.
     * @param oldScrollX Previous horizontal scroll origin.
     * @param oldScrollY Previous vertical scroll origin.
     */
    void onScrollChange(WebView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY);
}
}

There is no need to extend WebView. What about:

webView.getViewTreeObserver().addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
    @Override
    public void onScrollChanged() {
        Log.v(TAG, "+++ scrollchanged "+webView.getScrollY());
    }
});

Here is more elegant Kotlin version of accepted answer

class ObservableWebView @JvmOverloads constructor(
        context: Context,
        attrs: AttributeSet? = null,
        defStyleAttr: Int = 0
) : WebView(context, attrs, defStyleAttr) {
    var scrollListener: WebViewScrollListener? = null

    override fun onScrollChanged(scrollX: Int, scrollY: Int, oldScrollX: Int, oldScrollY: Int) {
        super.onScrollChanged(scrollX, scrollY, oldScrollX, oldScrollY)
        when {
            scrollY > oldScrollY -> scrollListener?.onScrollDown()
            scrollY < oldScrollY -> scrollListener?.onScrollUp()
        }
        scrollListener?.onScroll(scrollX, scrollY, oldScrollX, oldScrollY)
    }
}

interface WebViewScrollListener{
    fun onScroll(scrollX: Int, scrollY: Int, oldScrollX: Int, oldScrollY: Int)

    fun onScrollDown()

    fun onScrollUp()
}