图文讲解RecyclerView的复用机制 ||Recyclerview进阶

ViewHolder tryGetViewHolderForPositionByDeadline(int position, boolean dryRun, long deadlineNs) {
    ...
    if (mState.isPreLayout()) {     //动画相关
        holder = getChangedScrapViewForPosition(position);  //从缓存中拿吗？不应该不是缓存？
        fromScrapOrHiddenOrCache = holder != null;
    }
    // 1) Find by position from scrap/hidden list/cache
    if (holder == null) {
        holder = getScrapOrHiddenOrCachedHolderForPosition(position, dryRun); //从 attach 和 mCacheViews 中获取
        if (holder != null) {
            ... //校验这个holder是否可用
        }
    }
    if (holder == null) {
        ...
        final int type = mAdapter.getItemViewType(offsetPosition); //获取这个位置的数据的类型。 子Adapter复写的方法
        // 2) Find from scrap/cache via stable ids, if exists
        if (mAdapter.hasStableIds()) {    //stable id 就是标识一个viewholder的唯一性， 即使它做动画改变了位置
            holder = getScrapOrCachedViewForId(mAdapter.getItemId(offsetPosition),  //根据 stable id 从 scrap 和 mCacheViews中获取
                    type, dryRun);
            ....
        }
        if (holder == null && mViewCacheExtension != null) { // 从用户自定义的缓存集合中获取
            final View view = mViewCacheExtension
                    .getViewForPositionAndType(this, position, type);  //你返回的View要是RecyclerView.LayoutParams属性的
            if (view != null) {
                holder = getChildViewHolder(view);  //把它包装成一个ViewHolder
                ...
            }
        }
        if (holder == null) { // 从 RecyclerViewPool中获取
            holder = getRecycledViewPool().getRecycledView(type);
            ...
        }
        if (holder == null) { 
            ...
            //实在没有就会创建
            holder = mAdapter.createViewHolder(RecyclerView.this, type);
            ...
        }
    }
    ...
    boolean bound = false;
    if (mState.isPreLayout() && holder.isBound()) { //动画时不会想去调用 onBindData
        ...
    } else if (!holder.isBound() || holder.needsUpdate() || holder.isInvalid()) {
        ...
        final int offsetPosition = mAdapterHelper.findPositionOffset(position);
        bound = tryBindViewHolderByDeadline(holder, offsetPosition, position, deadlineNs);  //调用 bindData 方法
    }

    final ViewGroup.LayoutParams lp = holder.itemView.getLayoutParams();
    final LayoutParams rvLayoutParams;
    ...调整LayoutParams
    return holder;
}

dataSource.clear()
dataSource.addAll(newList)
adapter.notifyDatasetChanged()

void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
    ...
    onAnchorReady(recycler, state, mAnchorInfo, firstLayoutDirection);  // RecyclerView指定锚点，要准备正式布局了
    detachAndScrapAttachedViews(recycler);   // 在开始布局时，把所有的View都设置为 scrap 状态
    ...
}

public void detachAndScrapAttachedViews(@NonNull Recycler recycler) {
    for (int i = getChildCount() - 1; i >= 0; i--) {
        final View v = getChildAt(i);
        scrapOrRecycleView(recycler, i, v);
    }
}
private void scrapOrRecycleView(Recycler recycler, int index, View view) {
    final ViewHolder viewHolder = getChildViewHolderInt(view);
    ...删去了一些判断逻辑
    detachViewAt(index);  //设置RecyclerView这个位置的view的parent为null， 并标记ViewHolder为FLAG_TMP_DETACHED
    recycler.scrapView(view); //添加到mAttachedScrap集合中  
    ...
}

ViewHolder getScrapOrHiddenOrCachedHolderForPosition(int position, boolean dryRun) {
    final int scrapCount = mAttachedScrap.size();
    for (int i = 0; i < scrapCount; i++) {
        final ViewHolder holder = mAttachedScrap.get(i);
        if (!holder.wasReturnedFromScrap() && holder.getLayoutPosition() == position
                && !holder.isInvalid() && (mState.mInPreLayout || !holder.isRemoved())) {
            holder.addFlags(ViewHolder.FLAG_RETURNED_FROM_SCRAP);
            return holder;
        }
    }
    ...
}

int fill(RecyclerView.Recycler recycler, LayoutState layoutState,RecyclerView.State state, boolean stopOnFocusable) {
    ...
    int remainingSpace = layoutState.mAvailable + layoutState.mExtra;
    ...
    while ((layoutState.mInfinite || remainingSpace > 0) && layoutState.hasMore(state)) {
        ...
        layoutChunk(recycler, state, layoutState, layoutChunkResult); //填充一个子View

        if (layoutState.mScrollingOffset != LayoutState.SCROLLING_OFFSET_NaN) {
            layoutState.mScrollingOffset += layoutChunkResult.mConsumed;
            if (layoutState.mAvailable < 0) {
                layoutState.mScrollingOffset += layoutState.mAvailable;
            }
            recycleByLayoutState(recycler, layoutState); //根据滚动的距离来回收View
        }
    }
}