assistant-android/app/src/main/java/com/gh/common/view/NestedScrollWebView.java

package com.gh.common.view;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;

import androidx.core.view.MotionEventCompat;
import androidx.core.view.NestedScrollingChild;
import androidx.core.view.NestedScrollingChildHelper;
import androidx.core.view.ViewCompat;

import com.gh.common.view.dsbridge.DWebView;

public class NestedScrollWebView extends DWebView implements NestedScrollingChild {

    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 boolean mChange;

    private NestedScrollingChildHelper mChildHelper;

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

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


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

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        getParent().requestDisallowInterceptTouchEvent(true);
        return super.dispatchTouchEvent(ev);
    }

    @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);
                mChange = false;
                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];
                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];
                }
                if(mScrollConsumed[1]==0 && mScrollOffset[1]==0) {
                    if(mChange){
                        mChange =false;
                        trackedEvent.setAction(MotionEvent.ACTION_DOWN);
                        super.onTouchEvent(trackedEvent);
                    }else {
                        result = super.onTouchEvent(trackedEvent);
                    }
                    trackedEvent.recycle();
                }else{
                    if(Math.abs(mLastMotionY - y) >= 10) {
                        if (!mChange) {
                            mChange = true;
                            super.onTouchEvent(MotionEvent.obtain(0, 0, MotionEvent.ACTION_CANCEL, 0, 0, 0));
                        }
                    }

                }
                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);
    }

}