notifyDataSetChanged

notifyDataSetChanged和notifyItemChanged 區(qū)別

notifyDataSetChanged 調(diào)用到RecyclerViewDataObserver.onChanged()

@Override
public void onChanged() {
    assertNotInLayoutOrScroll(null);
    mState.mStructureChanged = true;

    setDataSetChangedAfterLayout();
    if (!mAdapterHelper.hasPendingUpdates()) {
        requestLayout();
    }
}

/**
 * Set to true when an adapter data set changed notification is received.
 * In that case, we cannot run any animations since we don't know what happened until layout.
 *
 * Attached items are invalid until next layout, at which point layout will animate/replace
 * items as necessary, building up content from the (effectively) new adapter from scratch.
 *
 * Cached items must be discarded when setting this to true, so that the cache may be freely
 * used by prefetching until the next layout occurs.
 *
 * @see #setDataSetChangedAfterLayout()
 */
boolean mDataSetHasChangedAfterLayout = false;

上面這個(gè)值會(huì)在adapter數(shù)據(jù)改變時(shí)設(shè)置為true ，dispatchLayoutStep3后設(shè)置為false

->RecyclerView.markKnownViewsInvalid() 所有子view的holder會(huì)添加

holder.addFlags(ViewHolder.FLAG_UPDATE | ViewHolder.FLAG_INVALID);

requestLayout被調(diào)用后走到LinearLayoutManager onLayoutChildren->RecyclerView.scrapOrRecycleView 中viewHolder.isInvalid()成立

recycleViewHolderInternal->putRecycledView ->ViewHolder.resetInternal()

這里將ViewHolder的mFlags置為0. 后續(xù)走到tryGetViewHolderForPositionByDeadline方法中

!holder.isBound()成立后重新走bindViewHolder方法慕的。所以notifyDataSetChanged會(huì)將可見(jiàn)的子view重新bind一次挡鞍。

notifyItemChanged 調(diào)用到 RecyclerViewDataObserve.onItemRangeChanged

AdapterHelper

boolean onItemRangeChanged(int positionStart, int itemCount, Object payload) {
    if (itemCount < 1) {
        return false;
    }
    mPendingUpdates.add(obtainUpdateOp(UpdateOp.UPDATE, positionStart, itemCount, payload));
    mExistingUpdateTypes |= UpdateOp.UPDATE;
    return mPendingUpdates.size() == 1;
}

調(diào)用requestLayout后

在processAdapterUpdatesAndSetAnimationFlags方法中AdpterHelper.preProcess,applyUpdate。調(diào)用Rv.findViewHolderForPosition找到當(dāng)前position的viewHolder,AdpterHelper.postponeAndUpdateViewHolders

范圍內(nèi)的holder 執(zhí)行 holder.addFlags(ViewHolder.FLAG_UPDATE);

void viewRangeUpdate(int positionStart, int itemCount, Object payload) {
    final int childCount = mChildHelper.getUnfilteredChildCount();
    final int positionEnd = positionStart + itemCount;

    for (int i = 0; i < childCount; i++) {
        final View child = mChildHelper.getUnfilteredChildAt(i);
        final ViewHolder holder = getChildViewHolderInt(child);
        if (holder == null || holder.shouldIgnore()) {
            continue;
        }
        if (holder.mPosition >= positionStart && holder.mPosition < positionEnd) {
            // We re-bind these view holders after pre-processing is complete so that
            // ViewHolders have their final positions assigned.
            holder.addFlags(ViewHolder.FLAG_UPDATE);
            holder.addChangePayload(payload);
            // lp cannot be null since we get ViewHolder from it.
            ((LayoutParams) child.getLayoutParams()).mInsetsDirty = true;
        }
    }
    mRecycler.viewRangeUpdate(positionStart, itemCount);
}

后續(xù)走到tryGetViewHolderForPositionByDeadline方法中holder.needsUpdate()成立重新走

bindViewHolder方法 所以notifyItemChanged只會(huì)去重新bind指定的view .

連續(xù)調(diào)用多次notifyItemChanged 每次調(diào)用會(huì)

mPendingUpdates.add(obtainUpdateOp(UpdateOp.UPDATE, positionStart, itemCount, payload));第一次回去調(diào)用requestLayout 缸兔。在preProcess中統(tǒng)一處理mPendingUpdates

holder.addFlags(ViewHolder.FLAG_UPDATE);

void preProcess() {
    mOpReorderer.reorderOps(mPendingUpdates);
    final int count = mPendingUpdates.size();
    for (int i = 0; i < count; i++) {
        UpdateOp op = mPendingUpdates.get(i);
        switch (op.cmd) {
            case UpdateOp.ADD:
                applyAdd(op);
                break;
            case UpdateOp.REMOVE:
                applyRemove(op);
                break;
            case UpdateOp.UPDATE:
                applyUpdate(op);
                break;
            case UpdateOp.MOVE:
                applyMove(op);
                break;
        }
        if (mOnItemProcessedCallback != null) {
            mOnItemProcessedCallback.run();
        }
    }
    mPendingUpdates.clear();
}

后續(xù)流程和上面一樣陨囊。

最近有個(gè)日歷加流水的需求爷怀，日歷可能本身就不太適合用RecyclerView寫，因?yàn)槭侨空故驹诮缑嫔系脑确Ｗ约和祽杏肦ecyclerView寫了 發(fā)現(xiàn)點(diǎn)擊反應(yīng)比較慢洒忧。排除了點(diǎn)擊事件分發(fā)問(wèn)題，發(fā)現(xiàn)每個(gè)子view bind一下還是要花個(gè)5-6ms帘撰。

image-20190409175715308.png

一個(gè)android.support.v7.widget.GridLayoutManager.layoutChunk耗時(shí)132ms 簡(jiǎn)直慘

image-20190409175936549.png

優(yōu)化后耗時(shí)需要變的耗時(shí)17ms跑慕，不需要改變的6ms。看來(lái)rv還是不適合這種場(chǎng)景

image-20190408215523156.png