Android自定義RecyclerView Item頭部懸浮吸頂

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);// 添加頭部View
}

/**
 * 設置RecyclerView的滾動監聽
 */
private void setListener() {
    mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            // 獲取頭部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()) {
                // 假如屏幕中顯示的第一個條目索引與當前獲取到的不一致, 就更新第一條目索引值
                mCurrentFirstVisibleIndex = mLayoutManager.findFirstVisibleItemPosition();
                if (mUpdateSuspensionBarListener != null) {
                    // 然後再更新懸掛條中的數據.
                    mUpdateSuspensionBarListener.updateSuspensionBar(mSuspensionBar, mCurrentFirstVisibleIndex);
                }
            }
            // 找到當前屏幕中顯示的第二條目
            View view = mLayoutManager.findViewByPosition(mCurrentFirstVisibleIndex + 1);
            if (view != null) {
                if (view.getTop() <= mSuspensionHeight) {
                    // 當前屏幕中第二Item離控件頂部距離如果小於懸掛條高度.
                    // 則懸掛條隨著RecyclerView的滾動移動, 這個懸掛條一直遮擋著Item條目的頭.
                    mSuspensionBar.setY(-(mSuspensionHeight - view.getTop()));
                    if (dy < 0) {
                        // 假如手指向下滑動, 剛好新的第一Item從屏幕頂端滑出來時,設置mSuspensionBar為透明.
                        mSuspensionBar.setAlpha(0);
                    }
                    //Log.e(TAG, "正在移動");
                } else {
                    // mSuspensionBar.getY() < 0 保證Alpha動畫不會多次執行
                    if (mSuspensionBar.getY() < 0) {
                        // 當前屏幕中第二Item離控件頂部距離如果大於懸掛條高度.
                        // 則懸掛調不需要移動,保持在控件頂部靜止不動.
                        mSuspensionBar.setY(0);
                        AlphaAnimation alphaAnimation = new AlphaAnimation(0, 1);
                        alphaAnimation.setDuration(1500);
                        mSuspensionBar.startAnimation(alphaAnimation);
                        //Log.e(TAG, "正在執行動畫");
                    } else {
                        // 這裡是當mSuspensionBar完全展示在屏幕中時候,設置為不透明
                        mSuspensionBar.setAlpha(1);
                        //Log.e(TAG, "mSuspensionBar.getY() > 0");
                    }
                }
            }
            //Log.e(TAG, "dy  " + dy);
        }
    });
}

/**
 * 設置Adapter
 *
 * @param mAdapter
 */
public void setAdapter(RecyclerView.Adapter mAdapter) {
    mRecyclerView.setAdapter(mAdapter);
    mRecyclerView.setHasFixedSize(true);
    if (mUpdateSuspensionBarListener != null) {
        // 更新懸掛條中的數據
        mUpdateSuspensionBarListener.updateSuspensionBar(mSuspensionBar, mCurrentFirstVisibleIndex);
    }
}

/**
 * 設置懸掛頭更新監聽
 *
 * @param updateSuspensionBarListener
 */
public void setUpdateSuspensionBarListener(UpdateSuspensionBarListener updateSuspensionBarListener) {
    this.mUpdateSuspensionBarListener = updateSuspensionBarListener;
}
public interface UpdateSuspensionBarListener {
    void updateSuspensionBar(View mSuspensionBar, int mFirstVisibleIndex);
}