NestedScrollWebView.java

package com.loopeer.codereader.ui.view;

import android.content.Context;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.NestedScrollingChild;
import android.support.v4.view.NestedScrollingChildHelper;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.webkit.WebView;

/*
* https://github.com/rhlff/NestedScrollWebView
* */
public class NestedScrollWebView extends WebView implements NestedScrollingChild {

    public interface ScrollChangeListener{
        void onScrollChanged(int l, int t, int oldl, int oldt);
    }

    public static final String TAG = NestedScrollWebView.class.getSimpleName();

    private int mLastMotionY;

    private final int[] mScrollOffset = new int[2];
    private final int[] mScrollConsumed = new int[2];

    private int mNestedYOffset;

    private NestedScrollingChildHelper mChildHelper;

    private ScrollChangeListener mScrollChangeListener;

    public NestedScrollWebView(Context context) {
        super(context);
        init();
    }

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

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

    private void init() {
        mChildHelper = new NestedScrollingChildHelper(this);
        setNestedScrollingEnabled(true);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        boolean result = false;

        MotionEvent trackedEvent = MotionEvent.obtain(event);

        final int action = MotionEventCompat.getActionMasked(event);

        if (action == MotionEvent.ACTION_DOWN) {
            mNestedYOffset = 0;
        }

        int y = (int) event.getY();

        event.offsetLocation(0, mNestedYOffset);

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mLastMotionY = y;
                startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
                result = super.onTouchEvent(event);
                break;
            case MotionEvent.ACTION_MOVE:
                int deltaY = mLastMotionY - y;

                if (dispatchNestedPreScroll(0, deltaY, mScrollConsumed, mScrollOffset)) {
                    deltaY -= mScrollConsumed[1];
                    trackedEvent.offsetLocation(0, mScrollOffset[1]);
                    mNestedYOffset += mScrollOffset[1];
                }

                int oldY = getScrollY();
                mLastMotionY = y - mScrollOffset[1];
                if (deltaY < 0) {
                    int newScrollY = Math.max(0, oldY + deltaY);
                    deltaY -= newScrollY - oldY;
                    if (dispatchNestedScroll(0, newScrollY - deltaY, 0, deltaY, mScrollOffset)) {
                        mLastMotionY -= mScrollOffset[1];
                        trackedEvent.offsetLocation(0, mScrollOffset[1]);
                        mNestedYOffset += mScrollOffset[1];
                    }
                }

                trackedEvent.recycle();
                result = super.onTouchEvent(trackedEvent);
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                stopNestedScroll();
                result = super.onTouchEvent(event);
                break;
        }
        return result;
    }

    // NestedScrollingChild

    @Override
    public void setNestedScrollingEnabled(boolean enabled) {
        mChildHelper.setNestedScrollingEnabled(enabled);
    }

    @Override
    public boolean isNestedScrollingEnabled() {
        return mChildHelper.isNestedScrollingEnabled();
    }

    @Override
    public boolean startNestedScroll(int axes) {
        return mChildHelper.startNestedScroll(axes);
    }

    @Override
    public void stopNestedScroll() {
        mChildHelper.stopNestedScroll();
    }

    @Override
    public boolean hasNestedScrollingParent() {
        return mChildHelper.hasNestedScrollingParent();
    }

    @Override
    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
        return mChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow);
    }

    @Override
    public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
        return mChildHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
    }

    @Override
    public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
        return mChildHelper.dispatchNestedFling(velocityX, velocityY, consumed);
    }

    @Override
    public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
        return mChildHelper.dispatchNestedPreFling(velocityX, velocityY);
    }

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

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

}