对于一个有限性列表，最长不大于10，做flutter的同事选择了逐个控件生成，自行构建list的方式来实现。
I/flutter (29896): ************callApi complete：2019-04-08 15:26:58.294069
I/flutter (29896): ************ips buildView：2019-04-08 15:26:58.605058
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.606843
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.612228
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.614787
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.617380
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.620302
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.623194
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.625957
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.628533
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.631107
I/flutter (29896): ************IpsItem build：2019-04-08 15:26:58.633696
整个过程耗时倒是也不算长，但是其实更新的Item只☝️个，逐个生成明显不太必要。
所以回去看了看RecyclerView是怎么考虑的单个数据更新，应该用的还是比较多的
mAdapter.notifyItemChanged(pos);
位于RecyclerView.Adapter
public final void notifyItemChanged(int position) {
mObservable.notifyItemRangeChanged(position, 1);
}
其中mObservable是AdapterDataObservable（继承自Observable）的对象
public void notifyItemRangeChanged(int positionStart, int itemCount) {
notifyItemRangeChanged(positionStart, itemCount, null);
}
public void notifyItemRangeChanged(int positionStart, int itemCount,
@Nullable Object payload) {
// since onItemRangeChanged() is implemented by the app, it could do anything, including
// removing itself from {@link mObservers} - and that could cause problems if
// an iterator is used on the ArrayList {@link mObservers}.
// to avoid such problems, just march thru the list in the reverse order.
for (int i = mObservers.size() - 1; i >= 0; i--) {
mObservers.get(i).onItemRangeChanged(positionStart, itemCount, payload);
}
}
mObservers.get(i)来自Observable
private class RecyclerViewDataObserver extends AdapterDataObserver {
RecyclerViewDataObserver() {
}
@Override
public void onChanged() {
assertNotInLayoutOrScroll(null);
mState.mStructureChanged = true;
processDataSetCompletelyChanged(true);
if (!mAdapterHelper.hasPendingUpdates()) {
requestLayout();
}
}
@Override
public void onItemRangeChanged(int positionStart, int itemCount, Object payload) {
assertNotInLayoutOrScroll(null);
if (mAdapterHelper.onItemRangeChanged(positionStart, itemCount, payload)) {
triggerUpdateProcessor();
}
}
@Override
public void onItemRangeInserted(int positionStart, int itemCount) {
assertNotInLayoutOrScroll(null);
if (mAdapterHelper.onItemRangeInserted(positionStart, itemCount)) {
triggerUpdateProcessor();
}
}
@Override
public void onItemRangeRemoved(int positionStart, int itemCount) {
assertNotInLayoutOrScroll(null);
if (mAdapterHelper.onItemRangeRemoved(positionStart, itemCount)) {
triggerUpdateProcessor();
}
}
@Override
public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
assertNotInLayoutOrScroll(null);
if (mAdapterHelper.onItemRangeMoved(fromPosition, toPosition, itemCount)) {
triggerUpdateProcessor();
}
}
void triggerUpdateProcessor() {
if (POST_UPDATES_ON_ANIMATION && mHasFixedSize && mIsAttached) {
ViewCompat.postOnAnimation(RecyclerView.this, mUpdateChildViewsRunnable);
} else {
mAdapterUpdateDuringMeasure = true;
requestLayout();
}
}
}
好，我们继续mAdapterHelper.onItemRangeChanged(positionStart, itemCount, payload)
/**
* @return True if updates should be processed.
*/
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;
}
在mPendingUpdates添加了个UpdateOp.UPDATE事件。
triggerUpdateProcessor
void triggerUpdateProcessor() {
if (POST_UPDATES_ON_ANIMATION && mHasFixedSize && mIsAttached) {
ViewCompat.postOnAnimation(RecyclerView.this, mUpdateChildViewsRunnable);
} else {
mAdapterUpdateDuringMeasure = true;
requestLayout();
}
}
static final boolean POST_UPDATES_ON_ANIMATION = Build.VERSION.SDK_INT >= 16;
由于我没有动过mHasFixedSize，所以它默认是false的。
public void setHasFixedSize(boolean hasFixedSize) {
mHasFixedSize = hasFixedSize;
}
也就是说整个方法最后走的是else, 即mAdapterUpdateDuringMeasure置为true。
马上我们在onMeasure里就见到它了。
@Override
protected void onMeasure(int widthSpec, int heightSpec) {
if (mLayout == null) {
defaultOnMeasure(widthSpec, heightSpec);
return;
}
if (mLayout.isAutoMeasureEnabled()) {
final int widthMode = MeasureSpec.getMode(widthSpec);
final int heightMode = MeasureSpec.getMode(heightSpec);
/**
* This specific call should be considered deprecated and replaced with
* {@link #defaultOnMeasure(int, int)}. It can't actually be replaced as it could
* break existing third party code but all documentation directs developers to not
* override {@link LayoutManager#onMeasure(int, int)} when
* {@link LayoutManager#isAutoMeasureEnabled()} returns true.
*/
mLayout.onMeasure(mRecycler, mState, widthSpec, heightSpec);
final boolean measureSpecModeIsExactly =
widthMode == MeasureSpec.EXACTLY && heightMode == MeasureSpec.EXACTLY;
if (measureSpecModeIsExactly || mAdapter == null) {
return;
}
if (mState.mLayoutStep == State.STEP_START) {
dispatchLayoutStep1();
}
// set dimensions in 2nd step. Pre-layout should happen with old dimensions for
// consistency
mLayout.setMeasureSpecs(widthSpec, heightSpec);
mState.mIsMeasuring = true;
dispatchLayoutStep2();
// now we can get the width and height from the children.
mLayout.setMeasuredDimensionFromChildren(widthSpec, heightSpec);
// if RecyclerView has non-exact width and height and if there is at least one child
// which also has non-exact width & height, we have to re-measure.
if (mLayout.shouldMeasureTwice()) {
mLayout.setMeasureSpecs(
MeasureSpec.makeMeasureSpec(getMeasuredWidth(), MeasureSpec.EXACTLY),
MeasureSpec.makeMeasureSpec(getMeasuredHeight(), MeasureSpec.EXACTLY));
mState.mIsMeasuring = true;
dispatchLayoutStep2();
// now we can get the width and height from the children.
mLayout.setMeasuredDimensionFromChildren(widthSpec, heightSpec);
}
} else {
if (mHasFixedSize) {
mLayout.onMeasure(mRecycler, mState, widthSpec, heightSpec);
return;
}
// custom onMeasure
// mAdapterUpdateDuringMeasure 这货我们刚才整成true了
if (mAdapterUpdateDuringMeasure) {
startInterceptRequestLayout();
onEnterLayoutOrScroll();
processAdapterUpdatesAndSetAnimationFlags(); // 我们看看这个
onExitLayoutOrScroll();
if (mState.mRunPredictiveAnimations) {
mState.mInPreLayout = true;
} else {
// consume remaining updates to provide a consistent state with the layout pass.
mAdapterHelper.consumeUpdatesInOnePass();
mState.mInPreLayout = false;
}
mAdapterUpdateDuringMeasure = false;
stopInterceptRequestLayout(false);
} else if (mState.mRunPredictiveAnimations) {
// If mAdapterUpdateDuringMeasure is false and mRunPredictiveAnimations is true:
// this means there is already an onMeasure() call performed to handle the pending
// adapter change, two onMeasure() calls can happen if RV is a child of LinearLayout
// with layout_width=MATCH_PARENT. RV cannot call LM.onMeasure() second time
// because getViewForPosition() will crash when LM uses a child to measure.
setMeasuredDimension(getMeasuredWidth(), getMeasuredHeight());
return;
}
if (mAdapter != null) {
mState.mItemCount = mAdapter.getItemCount();
} else {
mState.mItemCount = 0;
}
startInterceptRequestLayout();
mLayout.onMeasure(mRecycler, mState, widthSpec, heightSpec);
stopInterceptRequestLayout(false);
mState.mInPreLayout = false; // clear
}
}
private void processAdapterUpdatesAndSetAnimationFlags() {
if (mDataSetHasChangedAfterLayout) {
// Processing these items have no value since data set changed unexpectedly.
// Instead, we just reset it.
mAdapterHelper.reset();
if (mDispatchItemsChangedEvent) {
mLayout.onItemsChanged(this);
}
}
// simple animations are a subset of advanced animations (which will cause a
// pre-layout step)
// If layout supports predictive animations, pre-process to decide if we want to run them
if (predictiveItemAnimationsEnabled()) {
mAdapterHelper.preProcess();
} else {
mAdapterHelper.consumeUpdatesInOnePass(); // 走了这里
}
boolean animationTypeSupported = mItemsAddedOrRemoved || mItemsChanged;
mState.mRunSimpleAnimations = mFirstLayoutComplete
&& mItemAnimator != null
&& (mDataSetHasChangedAfterLayout
|| animationTypeSupported
|| mLayout.mRequestedSimpleAnimations)
&& (!mDataSetHasChangedAfterLayout
|| mAdapter.hasStableIds());
mState.mRunPredictiveAnimations = mState.mRunSimpleAnimations
&& animationTypeSupported
&& !mDataSetHasChangedAfterLayout
&& predictiveItemAnimationsEnabled();
}
private boolean predictiveItemAnimationsEnabled() {
return (mItemAnimator != null && mLayout.supportsPredictiveItemAnimations());
}
mItemAnimator 默认不为空 但是mLayout.supportsPredictiveItemAnimations()默认是false
ItemAnimator mItemAnimator = new DefaultItemAnimator();
/**
* @return true if this LayoutManager supports predictive item animations, false otherwise.
*/
public boolean supportsPredictiveItemAnimations() {
return false;
}
经上所述， 最后mAdapterHelper.consumeUpdatesInOnePass(), 记得咱们的事件是UpdateOp.UPDATE
AdapterHelper.java
/**
* Skips pre-processing and applies all updates in one pass.
*/
void consumeUpdatesInOnePass() {
// we still consume postponed updates (if there is) in case there was a pre-process call
// w/o a matching consumePostponedUpdates.
consumePostponedUpdates();
final int count = mPendingUpdates.size();
for (int i = 0; i < count; i++) {
UpdateOp op = mPendingUpdates.get(i);
switch (op.cmd) {
case UpdateOp.ADD:
mCallback.onDispatchSecondPass(op);
mCallback.offsetPositionsForAdd(op.positionStart, op.itemCount);
break;
case UpdateOp.REMOVE:
mCallback.onDispatchSecondPass(op);
mCallback.offsetPositionsForRemovingInvisible(op.positionStart, op.itemCount);
break;
case UpdateOp.UPDATE:
mCallback.onDispatchSecondPass(op);
mCallback.markViewHoldersUpdated(op.positionStart, op.itemCount, op.payload);
break;
case UpdateOp.MOVE:
mCallback.onDispatchSecondPass(op);
mCallback.offsetPositionsForMove(op.positionStart, op.itemCount);
break;
}
if (mOnItemProcessedCallback != null) {
mOnItemProcessedCallback.run();
}
}
recycleUpdateOpsAndClearList(mPendingUpdates);
mExistingUpdateTypes = 0;
}
callback肯定在RecyclerView里面
@Override
public void onDispatchSecondPass(AdapterHelper.UpdateOp op) {
dispatchUpdate(op);
}
void dispatchUpdate(AdapterHelper.UpdateOp op) {
switch (op.cmd) {
case AdapterHelper.UpdateOp.ADD:
mLayout.onItemsAdded(RecyclerView.this, op.positionStart, op.itemCount);
break;
case AdapterHelper.UpdateOp.REMOVE:
mLayout.onItemsRemoved(RecyclerView.this, op.positionStart, op.itemCount);
break;
case AdapterHelper.UpdateOp.UPDATE:
mLayout.onItemsUpdated(RecyclerView.this, op.positionStart, op.itemCount,
op.payload);
break;
case AdapterHelper.UpdateOp.MOVE:
mLayout.onItemsMoved(RecyclerView.this, op.positionStart, op.itemCount, 1);
break;
}
}
LayoutManager mLayout; layout 是layoutManager, onItemsUpdated也没复写好像没做什么。
@Override
public void markViewHoldersUpdated(int positionStart, int itemCount, Object payload) {
viewRangeUpdate(positionStart, itemCount, payload);
mItemsChanged = true;
}
/**
* Rebind existing views for the given range, or create as needed.
*
* @param positionStart Adapter position to start at
* @param itemCount Number of views that must explicitly be rebound
*/
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; // 是getItemDecorInsetsForChild里会用到的
}
}
mRecycler.viewRangeUpdate(positionStart, itemCount);
}
flag设置完以后就requestLayout了。关键点就是在哪里区分holder.addFlags(ViewHolder.FLAG_UPDATE);
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
TraceCompat.beginSection(TRACE_ON_LAYOUT_TAG);
dispatchLayout();
TraceCompat.endSection();
mFirstLayoutComplete = true;
}
void dispatchLayout() {
if (mAdapter == null) {
Log.e(TAG, "No adapter attached; skipping layout");
// leave the state in START
return;
}
if (mLayout == null) {
Log.e(TAG, "No layout manager attached; skipping layout");
// leave the state in START
return;
}
mState.mIsMeasuring = false;
if (mState.mLayoutStep == State.STEP_START) {
dispatchLayoutStep1();
mLayout.setExactMeasureSpecsFrom(this);
dispatchLayoutStep2();
} else if (mAdapterHelper.hasUpdates() || mLayout.getWidth() != getWidth()
|| mLayout.getHeight() != getHeight()) {
// First 2 steps are done in onMeasure but looks like we have to run again due to
// changed size.
mLayout.setExactMeasureSpecsFrom(this);
dispatchLayoutStep2();
} else {
// always make sure we sync them (to ensure mode is exact)
mLayout.setExactMeasureSpecsFrom(this);
}
dispatchLayoutStep3();
}
最正常的时候，刷新走的路径如下：
onMeasure
Element 4 set.
onLayout
onDraw
onDraw
偶尔不正常的时候，比如第一次调用，刷新走的路径会是两个Element被刷新了，我还没太细看，先记着：
onMeasure
Element 1 set.
Element 5 set.
onLayout
onDraw
onDraw
还是从log和stack来看，这样比较容易一把看完整个流程
@Override
public void onBindViewHolder(ViewHolder viewHolder, final int position) {
Log.d(TAG, "Element " + position + " set.", new RuntimeException());
}
RecyclerView
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
Log.d(TAG, "onLayout ");
}
onBindViewHolder其实是super.onLayout调用的。
at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6673)
at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6714)
at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5647)
at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5913)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5752)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5748)
at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2232)
at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1559)
at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1519)
at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:614)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3812)
at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3529)
at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:4082)
at com.mango.irene.recyclerviewdemo.MyRecyclerView.onLayout(MyRecyclerView.java:35)
at android.view.View.layout(View.java:17702)
at android.view.ViewGroup.layout(ViewGroup.java:5577)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
at android.view.View.layout(View.java:17702)
at android.view.ViewGroup.layout(ViewGroup.java:5577)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:17702)
at android.view.ViewGroup.layout(ViewGroup.java:5577)
at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:443)
at android.view.View.layout(View.java:17702)
at android.view.ViewGroup.layout(ViewGroup.java:5577)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at android.view.View.layout(View.java:17702)
at android.view.ViewGroup.layout(ViewGroup.java:5577)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
at android.view.View.layout(View.java:17702)
at android.view.ViewGroup.layout(ViewGroup.java:5577)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:729)
at android.view.View.layout(View.java:17702)
at android.view.ViewGroup.layout(ViewGroup.java:5577)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2426)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2148)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1334)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6499)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:934)
at android.view.Choreographer.doCallbacks(Choreographer.java:746)
at android.view.Choreographer.doFrame(Choreographer.java:677)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:920)
at android.os.Handler.handleCallback(Handler.java:754)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:163)
at android.app.ActivityThread.main(ActivityThread.java:6401)
真正用到ViewHolder.FLAG_UPDATE是在RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5913)
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);
}
这么多年也没怎么写过流程，这逻辑还是有点混乱。
不过初略上看明白应该问题不大，继续努力