public final class Recycler {

    // 存放可見范圍內(nèi)的 ViewHolder (但是在 onLayoutChildren 的時(shí)候，會(huì)將所有 View 都會(huì)緩存到這), 從這里復(fù)用的 ViewHolder 如果 position 或者 id 對(duì)應(yīng)的上，則不需要重新綁定數(shù)據(jù)。
    final ArrayList<ViewHolder> mAttachedScrap = new ArrayList<>();
    // 存放可見范圍內(nèi)并且數(shù)據(jù)發(fā)生了變化的 ViewHolder,從這里復(fù)用的 ViewHolder 需要重新綁定數(shù)據(jù)。
    ArrayList<ViewHolder> mChangedScrap = null;
    // 存放 remove 掉的 ViewHolder,從這里復(fù)用的 ViewHolder 如果 position 或者 id 對(duì)應(yīng)的上，則不需要重新綁定數(shù)據(jù)。
    final ArrayList<ViewHolder> mCachedViews = new ArrayList<ViewHolder>(); 
    // 默認(rèn)值是 2
    private int mRequestedCacheMax = DEFAULT_CACHE_SIZE; 
    // 默認(rèn)值是 2
    int mViewCacheMax = DEFAULT_CACHE_SIZE; 

    // 存放 remove 掉，并且重置了數(shù)據(jù)的 ViewHolder,從這里復(fù)用的 ViewHolder 需要重新綁定數(shù)據(jù)。 // 默認(rèn)值大小是 5 
    RecycledViewPool mRecyclerPool; 
    // 自定義的緩存
    private ViewCacheExtension mViewCacheExtension; 
    }

int fill(RecyclerView.Recycler recycler, LayoutState layoutState,
        RecyclerView.State state, boolean stopOnFocusable) {
    // max offset we should set is mFastScroll + available
    final int start = layoutState.mAvailable;
    //首選該語(yǔ)句塊的判斷，判斷當(dāng)前狀態(tài)是否為滾動(dòng)狀態(tài)，如果是的話，則觸發(fā) recycleByLayoutState 方法
    if (layoutState.mScrollingOffset != LayoutState.SCROLLING_OFFSET_NaN) {
        // TODO ugly bug fix. should not happen
        if (layoutState.mAvailable < 0) {
            layoutState.mScrollingOffset += layoutState.mAvailable;
        }
        // 分析1----回收
        recycleByLayoutState(recycler, layoutState);
        }
    while ((layoutState.mInfinite || remainingSpace > 0) && layoutState.hasMore(state)) {
        //分析2----復(fù)用
        layoutChunk(recycler, state, layoutState, layoutChunkResult);
    }
}

// 分析1----回收 
// 通過一步步追蹤，我們發(fā)現(xiàn)最后調(diào)用的是 removeAndRecycleViewAt() 
public void removeAndRecycleViewAt(int index, @NonNull Recycler recycler) {
    final View view = getChildAt(index);
    //分析1-1
    removeViewAt(index);
    //分析1-2
    recycler.recycleView(view);
}
// 分析1-1
// 從 RecyclerView 移除一個(gè) View 
public void removeViewAt(int index) {
    final View child = getChildAt(index);
    if (child != null) {
        mChildHelper.removeViewAt(index);
    }
}
//分析1-2 
// recycler.recycleView(view) 最終調(diào)用的是 recycleViewHolderInternal(holder) 進(jìn)行回收 VH (ViewHolder)
void recycleViewHolderInternal(ViewHolder holder) {
    if (forceRecycle || holder.isRecyclable()) {
        //判斷是否滿足放進(jìn) mCachedViews 
        if (mViewCacheMax > 0 && !holder.hasAnyOfTheFlags(ViewHolder.FLAG_INVALID| ViewHolder.FLAG_REMOVED| ViewHolder.FLAG_UPDATE| ViewHolder.FLAG_ADAPTER_POSITION_UNKNOWN)){
            // 判斷 mCachedViews 是否已滿
            if (cachedViewSize >= mViewCacheMax && cachedViewSize > 0) {
                // 如果滿了就將下標(biāo)為0（即最早加入的）移除，同時(shí)將其加入到 RecyclerPool 中
                recycleCachedViewAt(0);
                cachedViewSize--;
                }  
            mCachedViews.add(targetCacheIndex, holder);
            cached = true;
            }
        //如果沒有滿足上面的條件，則直接存進(jìn) RecyclerPool 中    
        if (!cached) {
            addViewHolderToRecycledViewPool(holder, true);
            recycled = true;
         } 
     }
}

//分析2
void layoutChunk(RecyclerView.Recycler recycler, RecyclerView.State state,
        LayoutState layoutState, LayoutChunkResult result) {
    //分析2-1
    View view = layoutState.next(recycler);
    if (layoutState.mScrapList == null) {
        if (mShouldReverseLayout == (layoutState.mLayoutDirection
                == LayoutState.LAYOUT_START)) {
            //添加到 RecyclerView 上
            addView(view);
        } else {
            addView(view, 0);
        }
    }
}
//分析2-1
//layoutState.next(recycler) 最后調(diào)用的是 tryGetViewHolderForPositionByDeadline() 這個(gè)方法正是 復(fù)用 核心的方法
ViewHolder tryGetViewHolderForPositionByDeadline(int position,
        boolean dryRun, long deadlineNs) {
    // 0) If there is a changed scrap, try to find from there
    // 例如：我們調(diào)用 notifyItemChanged 方法時(shí)
    if (mState.isPreLayout()) {
        // 如果是 changed 的 ViewHolder 那么就先從 mChangedScrap 中找
        holder = getChangedScrapViewForPosition(position);
        fromScrapOrHiddenOrCache = holder != null;
    }
    // 1) Find by position from scrap/hidden list/cache
    if (holder == null) {
        //如果在上面沒有找到(holder == null),那就嘗試從通過 pos 在 mAttachedScrap/ mHiddenViews / mCachedViews 中獲取
        holder = getScrapOrHiddenOrCachedHolderForPosition(position, dryRun);
    }
    if (holder == null) {
        // 2) Find from scrap/cache via stable ids, if exists
        if (mAdapter.hasStableIds()) {
            //如果在上面沒有找到(holder == null),那就嘗試從通過 id 在 mAttachedScrap/ mCachedViews 中獲取
            holder = getScrapOrCachedViewForId(mAdapter.getItemId(offsetPosition),
        }
        if (holder == null && mViewCacheExtension != null) {
            //這里是通過自定義緩存中獲取，忽略
        }
        //如果在上面都沒有找到(holder == null),那就嘗試在 RecycledViewPool 中獲取
        if (holder == null) { // fallback to pool
            holder = getRecycledViewPool().getRecycledView(type);
            if (holder != null) {
                //這里拿的是，要清空數(shù)據(jù)的
                holder.resetInternal();
            }
        }
        //如果在 Scrap / Hidden / Cache / RecycledViewPool 都沒有找到，那就只能創(chuàng)建一個(gè)了。
        if (holder == null) {
            holder = mAdapter.createViewHolder(RecyclerView.this, type);
        }
    }
    return holder;
}