/**
 * 自定義RecyclerView
 */
public class MyRecyclerView extends ViewGroup {
    
    public MyRecyclerView(Context context) {
        super(context);
    }
    public MyRecyclerView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

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

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {

    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return super.onTouchEvent(event);
    }
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return super.onInterceptTouchEvent(ev);
    }
    @Override
    public void scrollBy(int x, int y) {
        super.scrollBy(x, y);

    }
    interface Adapter<VH extends ViewHolder>{
        VH onCreateViewHolder(ViewGroup parent,int viewType);
        void onBindViewHolder(VH holder,int position);
        int getItemCount();
        int getItemViewType(int position);
    }
}

/**
 * 復(fù)用池
 */
public class MyRecyclerViewPool {
}

/**
 * Rv的ViewHolder
 */
public class ViewHolder {

    private View itemView;

    public ViewHolder(View itemView) {
        this.itemView = itemView;
    }
}

//持有Adapter和復(fù)用池的引用
private Adapter mAdapter;
private MyRecyclerViewPool myRecyclerViewPool;
//Rv的寬高
private int mWidth;
private int mHeight;
//itemView的高度
private int[] heights;

public void setAdapter(Adapter mAdapter) {
    this.mAdapter = mAdapter;
    this.needLayout = true;
    //刷新頁(yè)面
    requestLayout();
}

/**
 * 對(duì)子View進(jìn)行位置計(jì)算擺放
 * @param changed
 * @param l
 * @param t
 * @param r
 * @param b
 */
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    if(changed || needLayout){
        needLayout = false;
        mWidth = r - l;
        mHeight = b - t;
    }
}

 @Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
    if(changed || needLayout){
        needLayout = false;
        if(mAdapter != null){
            mWidth = r - l;
            mHeight = b - t;

            //計(jì)算每個(gè)ItemView的寬高，然后擺放位置
            rowCount = mAdapter.getItemCount();
            //這里假定每個(gè)ItemView的高度為200，實(shí)際Rv是需要測(cè)量每個(gè)ItemView的高度
            heights = new int[rowCount];
            for (int i = 0; i < rowCount; i++) {
                heights[i] = 200;
            }
            //擺放 -- 滿第一屏就停止擺放
            for (int i = 0; i < rowCount; i++) {
                bottom = top + heights[i];
                //獲取View
                ViewHolder holder = getItemView(i,0,top,mWidth,bottom);
                viewHolders.add(holder);
                //第二個(gè)top就是第一個(gè)的bottom
                top = bottom;
            }

        }
    }
}

private ViewHolder getItemView(int row,int left, int top, int right, int bottom) {

    ViewHolder viewHolder = obtainViewHolder(row,right - left,bottom - top);
    viewHolder.itemView.layout(left,top,right,bottom);
    return viewHolder;
}

private ViewHolder obtainViewHolder(int row, int width, int height) {

    ViewHolder viewHolder = null;
    //首先從復(fù)用池中查找

    //如果找不到，那么就通過(guò)適配器生成
    if(mAdapter !=null){
        viewHolder = mAdapter.onCreateViewHolder(this,mAdapter.getItemViewType(row));
    }
    return viewHolder;
}

/**
 * 復(fù)用池
 */
public class MyRecyclerViewPool {

    static class scrapData{
        List<ViewHolder> viewHolders = new ArrayList<>();
    }

    private SparseArray<scrapData> array = new SparseArray<>();

    /**
     * 從緩存中獲取ViewHolder
     * @param type ViewHolder的類(lèi)型，用戶自己設(shè)置
     * @return ViewHolder
     */
    public ViewHolder getRecyclerView(int type){

    }

    /**
     * 將ViewHolder放入緩存池中
     * @param holder
     */
    public void putRecyclerView(ViewHolder holder){

    }
}

/**
 * 從緩存中獲取ViewHolder
 *
 * @param type ViewHolder的類(lèi)型，用戶自己設(shè)置
 * @return ViewHolder
 */
public static ViewHolder getRecyclerView(int type) {
    //首先判斷type
    if (array.get(type) != null && !array.get(type).viewHolders.isEmpty()) {

        //將最后一個(gè)ViewHolder從列表中移除
        List<ViewHolder> scrapData = array.get(type).viewHolders;
        for (int i = scrapData.size() - 1; i >= 0; i--) {
            return scrapData.remove(i);
        }
    }
    return null;
}

/**
 * 將ViewHolder放入緩存池中
 *
 * @param holder
 */
public static void putRecyclerView(ViewHolder holder) {

    int key = holder.getItemViewType();
    //獲取集合
    List<ViewHolder> viewHolders = getScrapData(key).viewHolders;
    viewHolders.add(holder);
}

private static ScrapData getScrapData(int key) {
    ScrapData scrapData = array.get(key);
    if(scrapData == null){
        scrapData = new ScrapData();
        array.put(key,scrapData);
    }
    return scrapData;
}

private ViewHolder obtainViewHolder(int row, int width, int height) {

    int itemViewType = mAdapter.getItemViewType(row);
    //首先從復(fù)用池中查找
    ViewHolder viewHolder = MyRecyclerViewPool.getRecyclerView(itemViewType);
    //如果找不到，那么就通過(guò)適配器生成
    if(viewHolder == null){
        viewHolder = mAdapter.onCreateViewHolder(this,itemViewType);
    }
    //更新數(shù)據(jù)
    if (mAdapter != null) {
        mAdapter.onBindViewHolder(viewHolder, row);
        //設(shè)置ViewHOlder的類(lèi)型
        viewHolder.setItemViewType(itemViewType);

        //測(cè)量
        viewHolder.itemView.measure(
                MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY),
                MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY)
        );
        addView(viewHolder.itemView);
    }
    return viewHolder;
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {

    switch (ev.getAction()){

        case MotionEvent.ACTION_MOVE:
            return true;
    }
    return false;
}

private void init(Context context) {
    ViewConfiguration viewConfiguration = ViewConfiguration.get(context);
    this.touchSlop = viewConfiguration.getScaledTouchSlop();
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    //判斷是否攔截
    boolean intercept = false;

    switch (ev.getAction()){
        case MotionEvent.ACTION_DOWN:
            mCurrentY = (int) ev.getY();
            break;

        case MotionEvent.ACTION_MOVE:
            //y值在不停改變
            int y = (int) ev.getY();
            if(Math.abs(y - mCurrentY) > touchSlop){
                //認(rèn)為是滑動(dòng)了
                intercept = true;
            }
            break;
    }
    return intercept;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_MOVE: {
            //判斷滑動(dòng)的方向
            int diff = (int) (mCurrentY - event.getRawY());
            if(Math.abs(diff) > touchSlop){
                Log.e(TAG,"diff --- "+diff);
                scrollBy(0, diff);
                mCurrentY = (int) event.getRawY();
            }
            break;
        }
    }
    return super.onTouchEvent(event);
}

@Override
public void scrollBy(int x, int y) {
    super.scrollBy(x, y);
    scrollY += y;

    if (scrollY > 0) {
        Log.e(TAG, "上滑");
        //防止一次滑動(dòng)多個(gè)子View出去
        while (scrollY > heights[firstRow]) {
            //被移除，放入回收池
            if (!viewHolders.isEmpty()) {
                removeView(viewHolders.remove(0));
            }
            scrollY -= heights[firstRow];
            firstRow++;
        }

    } else {
        Log.e(TAG, "下滑");
    }
}

/**
 * 移除ViewHolder，放入回收池
 *
 * @param holder
 */
private void removeView(ViewHolder holder) {
    MyRecyclerViewPool.putRecyclerView(holder);
    //系統(tǒng)方法，從RecyclerView中移除這個(gè)View
    removeView(holder.itemView);
    viewHolders.remove(holder);
}

 //如果小于屏幕的高度
 while (getRealHeight(firstRow) <= mHeight) {
     //觸發(fā)加載機(jī)制
     int addIndex = firstRow + viewHolders.size();
     ViewHolder viewHolder = obtainViewHolder(addIndex, mWidth, heights[addIndex]);
     viewHolders.add(viewHolders.size(), viewHolder);
     Log.e(TAG,"添加一個(gè)View");
 }
/**
 * 獲取實(shí)際展示的高度
 *
 * @param firstIndex
 * @return
 */
private int getRealHeight(int firstIndex) {
    return getSumArray(firstRow, viewHolders.size()) - scrollY;
}

private int getSumArray(int firstIndex, int count) {
    int totalHeight = 0;
    count+= firstIndex;
    for (int i = firstIndex; i < count; i++) {
        totalHeight += heights[i];
    }
    return totalHeight;
}

/**
 * 重新擺放View
 */
private void repositionViews() {
    int left = 0;
    int top = -scrollY;
    int right = mWidth;
    int bottom = 0;

    int index = firstRow;

    for (int i = 0; i < viewHolders.size(); i++) {
        bottom = top + heights[index++];
        viewHolders.get(i).itemView.layout(left,top,right,bottom);
        top = bottom;
    }
}

//下滑頂部添加View
while (scrollY < 0) {

    //獲取ViewHolder
    ViewHolder viewHolder = obtainViewHolder(firstRow - 1, mWidth, heights[firstRow - 1]);
    //放到屏幕緩存ViewHolder最頂部的位置
    viewHolders.add(0, viewHolder);
    firstRow--;
    //當(dāng)頂部ItemView完全加進(jìn)來(lái)之后，需要改變scrollY的值
    scrollY += heights[firstRow];
}

//底部移除View
while (!viewHolders.isEmpty() &&
        getRealHeight(firstRow) - viewHolders.get(viewHolders.size() - 1).itemView.getHeight() >= mHeight) {
    //需要移除
    removeView(viewHolders.remove(viewHolders.size() - 1));
}

/**
 * @param scrollY
 * @param firstRow
 */
private void scrollBounds(int scrollY, int firstRow) {

    if (scrollY > 0) {
        //上滑
        if (getSumArray(firstRow, heights.length - firstRow) - scrollY > mHeight) {
            this.scrollY = scrollY;
        } else {
            this.scrollY = getSumArray(firstRow, heights.length - firstRow) - mHeight;
        }
    } else {
        //下滑
        this.scrollY = Math.max(scrollY, -getSumArray(0, firstRow));
    }
}

 @Override
 public void scrollBy(int x, int y) {
//        super.scrollBy(x, y);

     scrollY += y;
     scrollBounds(scrollY, firstRow);


     if (scrollY > 0) {
         Log.e(TAG, "上滑");
         //防止一次滑動(dòng)多個(gè)子View出去
         while (scrollY > heights[firstRow]) {
             //被移除，放入回收池
             if (!viewHolders.isEmpty()) {
                 removeView(viewHolders.remove(0));
             }
             scrollY -= heights[firstRow];
             firstRow++;
             Log.e("scrollBy", "scrollBy 移除一個(gè)View size =="+viewHolders.size());
         }

         //如果小于屏幕的高度
         while (getRealHeight(firstRow) < mHeight) {
             //觸發(fā)加載機(jī)制
             int addIndex = firstRow + viewHolders.size();
             ViewHolder viewHolder = obtainViewHolder(addIndex, mWidth, heights[addIndex]);
             viewHolders.add(viewHolders.size(), viewHolder);
             Log.e("scrollBy", "scrollBy 添加一個(gè)View size=="+viewHolders.size());
         }
         //重新擺放
         repositionViews();

     } else {
         Log.e(TAG, "下滑");

         //底部移除View
         while (!viewHolders.isEmpty() &&
                 getRealHeight(firstRow) - viewHolders.get(viewHolders.size() - 1).itemView.getHeight() >= mHeight) {
             //需要移除
             removeView(viewHolders.remove(viewHolders.size() - 1));
         }

         //下滑頂部添加View
         while (scrollY < 0) {

             //獲取ViewHolder
             ViewHolder viewHolder = obtainViewHolder(firstRow - 1, mWidth, heights[firstRow - 1]);
             //放到屏幕緩存ViewHolder最頂部的位置
             viewHolders.add(0, viewHolder);
             firstRow--;
             //當(dāng)頂部ItemView完全加進(jìn)來(lái)之后，需要改變scrollY的值
             scrollY += heights[firstRow];
         }
     }
 }