WebView无法在SwipeRefreshLayout中向下滚动

public class CustomWebView extends WebView {
    private float mDownX;
    private float mDownY;
    private boolean mIsBeingDragged;

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

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

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mDownX = event.getX();
                mDownY = event.getY();
                mIsBeingDragged = false;
                break;
            case MotionEvent.ACTION_MOVE:
                float deltaX = event.getX() - mDownX;
                float deltaY = event.getY() - mDownY;
                if (!mIsBeingDragged && Math.abs(deltaY) > Math.abs(deltaX)) {
                    mIsBeingDragged = true;
                    getParent().requestDisallowInterceptTouchEvent(true);
                }
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                mIsBeingDragged = false;
                break;
        }
        return super.onTouchEvent(event);
    }
}