复用实现
- RecyclerView怎么加载数据的？
- RecyclerView复用机制
- RecyclerView三级缓存
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ViewHolder tryGetViewHolderForPositionByDeadline(int position,
boolean dryRun, long deadlineNs) {
if (position < 0 || position >= mState.getItemCount()) {
throw new IndexOutOfBoundsException("Invalid item position " + position
+ "(" + position + "). Item count:" + mState.getItemCount()
+ exceptionLabel());
}
boolean fromScrapOrHiddenOrCache = false;
ViewHolder holder = null;
// 0) If there is a changed scrap, try to find from there
if (mState.isPreLayout()) {
holder = getChangedScrapViewForPosition(position);
fromScrapOrHiddenOrCache = holder != null;
}
// 1) Find by position from scrap/hidden list/cache
if (holder == null) {
holder = getScrapOrHiddenOrCachedHolderForPosition(position, dryRun);
if (holder != null) {
if (!validateViewHolderForOffsetPosition(holder)) {
// recycle holder (and unscrap if relevant) since it can't be used
if (!dryRun) {
// we would like to recycle this but need to make sure it is not used by
// animation logic etc.
holder.addFlags(ViewHolder.FLAG_INVALID);
if (holder.isScrap()) {
removeDetachedView(holder.itemView, false);
holder.unScrap();
} else if (holder.wasReturnedFromScrap()) {
holder.clearReturnedFromScrapFlag();
}
recycleViewHolderInternal(holder);
}
holder = null;
} else {
fromScrapOrHiddenOrCache = true;
}
}
}
if (holder == null) {
final int offsetPosition = mAdapterHelper.findPositionOffset(position);
if (offsetPosition < 0 || offsetPosition >= mAdapter.getItemCount()) {
throw new IndexOutOfBoundsException("Inconsistency detected. Invalid item "
+ "position " + position + "(offset:" + offsetPosition + ")."
+ "state:" + mState.getItemCount() + exceptionLabel());
}
final int type = mAdapter.getItemViewType(offsetPosition);
// 2) Find from scrap/cache via stable ids, if exists
if (mAdapter.hasStableIds()) {
holder = getScrapOrCachedViewForId(mAdapter.getItemId(offsetPosition),
type, dryRun);
if (holder != null) {
// update position
holder.mPosition = offsetPosition;
fromScrapOrHiddenOrCache = true;
}
}
if (holder == null && mViewCacheExtension != null) {
// We are NOT sending the offsetPosition because LayoutManager does not
// know it.
final View view = mViewCacheExtension
.getViewForPositionAndType(this, position, type);
if (view != null) {
holder = getChildViewHolder(view);
if (holder == null) {
throw new IllegalArgumentException("getViewForPositionAndType returned"
+ " a view which does not have a ViewHolder"
+ exceptionLabel());
} else if (holder.shouldIgnore()) {
throw new IllegalArgumentException("getViewForPositionAndType returned"
+ " a view that is ignored. You must call stopIgnoring before"
+ " returning this view." + exceptionLabel());
}
}
}
if (holder == null) { // fallback to pool
if (DEBUG) {
Log.d(TAG, "tryGetViewHolderForPositionByDeadline("
+ position + ") fetching from shared pool");
}
holder = getRecycledViewPool().getRecycledView(type);
if (holder != null) {
holder.resetInternal();
if (FORCE_INVALIDATE_DISPLAY_LIST) {
invalidateDisplayListInt(holder);
}
}
}
if (holder == null) {
long start = getNanoTime();
if (deadlineNs != FOREVER_NS
&& !mRecyclerPool.willCreateInTime(type, start, deadlineNs)) {
// abort - we have a deadline we can't meet
return null;
}
holder = mAdapter.createViewHolder(RecyclerView.this, type);
if (ALLOW_THREAD_GAP_WORK) {
// only bother finding nested RV if prefetching
RecyclerView innerView = findNestedRecyclerView(holder.itemView);
if (innerView != null) {
holder.mNestedRecyclerView = new WeakReference<>(innerView);
}
}
long end = getNanoTime();
mRecyclerPool.factorInCreateTime(type, end - start);
if (DEBUG) {
Log.d(TAG, "tryGetViewHolderForPositionByDeadline created new ViewHolder");
}
}
}
// This is very ugly but the only place we can grab this information
// before the View is rebound and returned to the LayoutManager for post layout ops.
// We don't need this in pre-layout since the VH is not updated by the LM.
if (fromScrapOrHiddenOrCache && !mState.isPreLayout() && holder
.hasAnyOfTheFlags(ViewHolder.FLAG_BOUNCED_FROM_HIDDEN_LIST)) {
holder.setFlags(0, ViewHolder.FLAG_BOUNCED_FROM_HIDDEN_LIST);
if (mState.mRunSimpleAnimations) {
int changeFlags = ItemAnimator
.buildAdapterChangeFlagsForAnimations(holder);
changeFlags |= ItemAnimator.FLAG_APPEARED_IN_PRE_LAYOUT;
final ItemHolderInfo info = mItemAnimator.recordPreLayoutInformation(mState,
holder, changeFlags, holder.getUnmodifiedPayloads());
recordAnimationInfoIfBouncedHiddenView(holder, info);
}
}
boolean bound = false;
if (mState.isPreLayout() && holder.isBound()) {
// do not update unless we absolutely have to.
holder.mPreLayoutPosition = position;
} else if (!holder.isBound() || holder.needsUpdate() || holder.isInvalid()) {
if (DEBUG && holder.isRemoved()) {
throw new IllegalStateException("Removed holder should be bound and it should"
+ " come here only in pre-layout. Holder: " + holder
+ exceptionLabel());
}
final int offsetPosition = mAdapterHelper.findPositionOffset(position);
bound = tryBindViewHolderByDeadline(holder, offsetPosition, position, deadlineNs);
}
final ViewGroup.LayoutParams lp = holder.itemView.getLayoutParams();
final LayoutParams rvLayoutParams;
if (lp == null) {
rvLayoutParams = (LayoutParams) generateDefaultLayoutParams();
holder.itemView.setLayoutParams(rvLayoutParams);
} else if (!checkLayoutParams(lp)) {
rvLayoutParams = (LayoutParams) generateLayoutParams(lp);
holder.itemView.setLayoutParams(rvLayoutParams);
} else {
rvLayoutParams = (LayoutParams) lp;
}
rvLayoutParams.mViewHolder = holder;
rvLayoutParams.mPendingInvalidate = fromScrapOrHiddenOrCache && bound;
return holder;
}
mRecyclerPool：这个也很重要，但存在这里的 ViewHolder 的数据信息会被重置掉，相当于 ViewHolder 是一个重创新建的一样，所以需要重新调用 onBindViewHolder 来绑定数据。
动画问题
分为4种动画。
触摸时间分发，解决滑动冲突
卡顿优化
-
Item 布局复杂性？ 尽量减少布局嵌套，层级越深，每次测量时间久越久。如果布局很复杂，可以考虑自定义布局能不能实现。尽量减少过度绘制区域。这个可以在开发者选项中看到：调试GPU过度绘制 图片加载的优化，不仅仅是图片加载，应该说是列表在滚动过程中，如果布局很复杂，而且样式也很多，那就需要考虑滚动的时候不做复杂布局及图片的加载，尽量减少滚动过程中的耗时操作，这样滚动停止的时候再加载可见区域的布局，因为这个时候是停止状态，即使略微耗时一些用户的感知也是比较小的，就会给人一种不卡的假象。
-
滑动卡顿有什么排查方式吗？
fps检测，方法执行时间。布局优化
-
事件的延迟处理？
post当view已经绘制完成在界面展示好后再去加载数据。
-
增大缓存值
-
滑动时不加载次重要数据
-
局部更新
数据加载优化
- 延迟加载
-
分页加载
-
怎么优化方式？
- 线程池的复用？