Android自定义RecyclerView Item头部悬浮吸顶

public SuspensionBarRecyclerView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.SuspensionBarRecyclerView, defStyleAttr, 0);
    mResSuspensionBar = typedArray.getResourceId(R.styleable.SuspensionBarRecyclerView_sbrv_bar, R.layout.sbrv_default_bar);
    mSuspensionBarHeight = typedArray.getLayoutDimension(R.styleable.SuspensionBarRecyclerView_sbrv_bar_height, ViewGroup.LayoutParams.WRAP_CONTENT);
    typedArray.recycle();
    initView(context);
    setListener();
}

private void initView(Context context) {
    mSuspensionBar = LayoutInflater.from(context).inflate(mResSuspensionBar, null);
    mRecyclerView = new RecyclerView(context);
    mLayoutManager = new LinearLayoutManager(context);
    mRecyclerView.setLayoutManager(mLayoutManager);
    this.addView(mRecyclerView, 0);// 添加RecyclerView
    this.addView(mSuspensionBar, 1);// 添加头部View
}

/**
 * 设置RecyclerView的滚动监听
 */
private void setListener() {
    mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            // 获取头部View的高度
            mSuspensionHeight = mSuspensionBar.getHeight();
        }
        @Override
        public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            if (mCurrentFirstVisibleIndex != mLayoutManager.findFirstVisibleItemPosition()) {
                // 假如屏幕中显示的第一个条目索引与当前获取到的不一致, 就更新第一条目索引值
                mCurrentFirstVisibleIndex = mLayoutManager.findFirstVisibleItemPosition();
                if (mUpdateSuspensionBarListener != null) {
                    // 然后再更新悬挂条中的数据.
                    mUpdateSuspensionBarListener.updateSuspensionBar(mSuspensionBar, mCurrentFirstVisibleIndex);
                }
            }
            // 找到当前屏幕中显示的第二条目
            View view = mLayoutManager.findViewByPosition(mCurrentFirstVisibleIndex + 1);
            if (view != null) {
                if (view.getTop() <= mSuspensionHeight) {
                    // 当前屏幕中第二Item离控件顶部距离如果小于悬挂条高度.
                    // 则悬挂条随着RecyclerView的滚动移动, 这个悬挂条一直遮挡着Item条目的头.
                    mSuspensionBar.setY(-(mSuspensionHeight - view.getTop()));
                    if (dy < 0) {
                        // 假如手指向下滑动, 刚好新的第一Item从屏幕顶端滑出来时,设置mSuspensionBar为透明.
                        mSuspensionBar.setAlpha(0);
                    }
                    //Log.e(TAG, "正在移动");
                } else {
                    // mSuspensionBar.getY() < 0 保证Alpha动画不会多次执行
                    if (mSuspensionBar.getY() < 0) {
                        // 当前屏幕中第二Item离控件顶部距离如果大于悬挂条高度.
                        // 则悬挂调不需要移动,保持在控件顶部静止不动.
                        mSuspensionBar.setY(0);
                        AlphaAnimation alphaAnimation = new AlphaAnimation(0, 1);
                        alphaAnimation.setDuration(1500);
                        mSuspensionBar.startAnimation(alphaAnimation);
                        //Log.e(TAG, "正在执行动画");
                    } else {
                        // 这里是当mSuspensionBar完全展示在屏幕中时候,设置为不透明
                        mSuspensionBar.setAlpha(1);
                        //Log.e(TAG, "mSuspensionBar.getY() > 0");
                    }
                }
            }
            //Log.e(TAG, "dy  " + dy);
        }
    });
}

/**
 * 设置Adapter
 *
 * @param mAdapter
 */
public void setAdapter(RecyclerView.Adapter mAdapter) {
    mRecyclerView.setAdapter(mAdapter);
    mRecyclerView.setHasFixedSize(true);
    if (mUpdateSuspensionBarListener != null) {
        // 更新悬挂条中的数据
        mUpdateSuspensionBarListener.updateSuspensionBar(mSuspensionBar, mCurrentFirstVisibleIndex);
    }
}

/**
 * 设置悬挂头更新监听
 *
 * @param updateSuspensionBarListener
 */
public void setUpdateSuspensionBarListener(UpdateSuspensionBarListener updateSuspensionBarListener) {
    this.mUpdateSuspensionBarListener = updateSuspensionBarListener;
}
public interface UpdateSuspensionBarListener {
    void updateSuspensionBar(View mSuspensionBar, int mFirstVisibleIndex);
}