为了更好的理解这个问题出现的真正原因，建议首先看看下面两篇文章：
浅析notifyDataSetChanged内部工作流程
ListView中requestLayout执行流程解析
综合上面两篇文章，我们可以把整个执行过程用下图展示出来。这个图非常的关键，一定要保证在看下文的时候已经理解了上图的过程。
下面看看错误提示。
07-28 17:22:02.162: E/AndroidRuntime(16779): java.lang.IllegalStateException: The content of the adapter has changed but ListView did not receive a notification. Make sure the content of your adapter is not modified from a background thread, but only from the UI thread. Make sure your adapter calls notifyDataSetChanged() when its content changes. [in ListView(2131034604, class android.widget.ListView) with Adapter(class com.nodin.sarah.HeartListAdapter)]
这个问题就是当我们调用notifyDataSetChanged()的过程中，数据源可能发生了改变，这样出现前后数据源不一致而报错，可能这样说还是不好理解，下面我们可以从源码的角度来进行分析。
从浅析notifyDataSetChanged内部工作流程文章中我们需要理出以下两点：
当执行notifyDataSetChanged()，它内部做了两件事情,具体的代码在AdapterDataSetObserver的onChanged方法里面：
1、mDataChanged = true;
mOldItemCount = mItemCount;
mItemCount = getAdapter().getCount();
2、requestLayout();
可以看到做完这两件事情后，它进入了requestLayout()方法中，requestLayout方法中做了什么事情，这里就不细说，看看ListView中requestLayout执行流程解析这篇文章应该就知道了，从上图可以知道，requestLayout内部其实就是执行了performTraversals(),performTraversals()内部执行的就是measure,layout,draw方法，onMeasure()用于测量View的大小，onLayout()用于确定View的布局，onDraw()用于将View绘制到界面上。而在ListView当中，onMeasure()并没有什么特殊的地方，因为它终归是一个View，占用的空间最多并且通常也就是整个屏幕。onDraw()在ListView当中也没有什么意义，因为ListView本身并不负责绘制，而是由ListView当中的子元素来进行绘制的。那么ListView大部分的功能其实都是在onLayout()方法中进行的了,所以我重点关注到onLayout()方法，从图知道它执行了layoutChildren()方法。
ListView中是没有onLayout()这个方法的，这是因为这个方法是在ListView的父类AbsListView中实现的,我们来跟跟源码：
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
mInLayout = true;
if (changed) {
int childCount = getChildCount();
for (int i = ; i < childCount; i++) {
getChildAt(i).forceLayout();
}
mRecycler.markChildrenDirty();
}
if (mFastScroller != null && (mItemCount != mOldItemCount || mDataChanged)) {
mFastScroller.onItemCountChanged(mItemCount);
}
//这个方法是重点
layoutChildren();
mInLayout = false;
mOverscrollMax = (b - t) / OVERSCROLL_LIMIT_DIVISOR;
}
onLayout()方法中并没有做什么复杂的逻辑操作，主要就是一个判断，如果ListView的大小或者位置发生了变化，那么changed变量就会变成true，此时会要求所有的子布局都强制进行重绘。重点调用了layoutChildren()这个方法，从方法名上我们就可以猜出这个方法是用来进行子元素布局的，不过进入到这个方法当中你会发现这是个空方法，没有一行代码。这当然是可以理解的了，因为子元素的布局应该是由具体的实现类来负责完成的，而不是由父类完成。那么进入ListView的layoutChildren()方法。
@Override
protected void layoutChildren() {
final boolean blockLayoutRequests = mBlockLayoutRequests;
if (blockLayoutRequests) {
return;
}
mBlockLayoutRequests = true;
try {
super.layoutChildren();
invalidate();
if (mAdapter == null) {
resetList();
invokeOnItemScrollListener();
return;
}
final int childrenTop = mListPadding.top;
final int childrenBottom = mBottom - mTop - mListPadding.bottom;
final int childCount = getChildCount();
int index = ;
int delta = ;
View sel;
View oldSel = null;
View oldFirst = null;
View newSel = null;
// Remember stuff we will need down below
switch (mLayoutMode) {
case LAYOUT_SET_SELECTION:
index = mNextSelectedPosition - mFirstPosition;
if (index >= && index < childCount) {
newSel = getChildAt(index);
}
break;
case LAYOUT_FORCE_TOP:
case LAYOUT_FORCE_BOTTOM:
case LAYOUT_SPECIFIC:
case LAYOUT_SYNC:
break;
case LAYOUT_MOVE_SELECTION:
default:
// Remember the previously selected view
index = mSelectedPosition - mFirstPosition;
if (index >= && index < childCount) {
oldSel = getChildAt(index);
}
// Remember the previous first child
oldFirst = getChildAt();
if (mNextSelectedPosition >= ) {
delta = mNextSelectedPosition - mSelectedPosition;
}
// Caution: newSel might be null
newSel = getChildAt(index + delta);
}
boolean dataChanged = mDataChanged;
if (dataChanged) {
handleDataChanged();
}
// Handle the empty set by removing all views that are visible
// and calling it a day
if (mItemCount == ) {
resetList();
invokeOnItemScrollListener();
return;
} else if (mItemCount != mAdapter.getCount()) {
throw new IllegalStateException("The content of the adapter has changed but "
+ "ListView did not receive a notification. Make sure the content of "
+ "your adapter is not modified from a background thread, but only from "
+ "the UI thread. Make sure your adapter calls notifyDataSetChanged() "
+ "when its content changes. [in ListView(" + getId() + ", " + getClass()
+ ") with Adapter(" + mAdapter.getClass() + ")]");
}
setSelectedPositionInt(mNextSelectedPosition);
// Remember which child, if any, had accessibility focus.
final int accessibilityFocusPosition;
final View accessFocusedChild = getAccessibilityFocusedChild();
if (accessFocusedChild != null) {
accessibilityFocusPosition = getPositionForView(accessFocusedChild);
accessFocusedChild.setHasTransientState(true);
} else {
accessibilityFocusPosition = INVALID_POSITION;
}
// Ensure the child containing focus, if any, has transient state.
// If the list data hasn't changed, or if the adapter has stable
// IDs, this will maintain focus.
final View focusedChild = getFocusedChild();
if (focusedChild != null) {
focusedChild.setHasTransientState(true);
}
// Pull all children into the RecycleBin.
// These views will be reused if possible
final int firstPosition = mFirstPosition;
final RecycleBin recycleBin = mRecycler;
if (dataChanged) {
for (int i = ; i < childCount; i++) {
recycleBin.addScrapView(getChildAt(i), firstPosition+i);
}
} else {
recycleBin.fillActiveViews(childCount, firstPosition);
}
// Clear out old views
detachAllViewsFromParent();
recycleBin.removeSkippedScrap();
switch (mLayoutMode) {
case LAYOUT_SET_SELECTION:
if (newSel != null) {
sel = fillFromSelection(newSel.getTop(), childrenTop, childrenBottom);
} else {
sel = fillFromMiddle(childrenTop, childrenBottom);
}
break;
case LAYOUT_SYNC:
sel = fillSpecific(mSyncPosition, mSpecificTop);
break;
case LAYOUT_FORCE_BOTTOM:
sel = fillUp(mItemCount - , childrenBottom);
adjustViewsUpOrDown();
break;
case LAYOUT_FORCE_TOP:
mFirstPosition = ;
sel = fillFromTop(childrenTop);
adjustViewsUpOrDown();
break;
case LAYOUT_SPECIFIC:
sel = fillSpecific(reconcileSelectedPosition(), mSpecificTop);
break;
case LAYOUT_MOVE_SELECTION:
sel = moveSelection(oldSel, newSel, delta, childrenTop, childrenBottom);
break;
default:
if (childCount == ) {
if (!mStackFromBottom) {
final int position = lookForSelectablePosition(, true);
setSelectedPositionInt(position);
sel = fillFromTop(childrenTop);
} else {
final int position = lookForSelectablePosition(mItemCount - , false);
setSelectedPositionInt(position);
sel = fillUp(mItemCount - , childrenBottom);
}
} else {
if (mSelectedPosition >= && mSelectedPosition < mItemCount) {
sel = fillSpecific(mSelectedPosition,
oldSel == null ? childrenTop : oldSel.getTop());
} else if (mFirstPosition < mItemCount) {
sel = fillSpecific(mFirstPosition,
oldFirst == null ? childrenTop : oldFirst.getTop());
} else {
sel = fillSpecific(, childrenTop);
}
}
break;
}
// Flush any cached views that did not get reused above
recycleBin.scrapActiveViews();
if (sel != null) {
final boolean shouldPlaceFocus = mItemsCanFocus && hasFocus();
final boolean maintainedFocus = focusedChild != null && focusedChild.hasFocus();
if (shouldPlaceFocus && !maintainedFocus && !sel.hasFocus()) {
if (sel.requestFocus()) {
// Successfully placed focus, clear selection.
sel.setSelected(false);
mSelectorRect.setEmpty();
} else {
// Failed to place focus, clear current (invalid) focus.
final View focused = getFocusedChild();
if (focused != null) {
focused.clearFocus();
}
positionSelector(INVALID_POSITION, sel);
}
} else {
positionSelector(INVALID_POSITION, sel);
}
mSelectedTop = sel.getTop();
} else {
// If the user's finger is down, select the motion position.
// Otherwise, clear selection.
if (mTouchMode == TOUCH_MODE_TAP || mTouchMode == TOUCH_MODE_DONE_WAITING) {
final View child = getChildAt(mMotionPosition - mFirstPosition);
if (child != null) {
positionSelector(mMotionPosition, child);
}
} else {
mSelectedTop = ;
mSelectorRect.setEmpty();
}
}
if (accessFocusedChild != null) {
accessFocusedChild.setHasTransientState(false);
// If we failed to maintain accessibility focus on the previous
// view, attempt to restore it to the previous position.
if (!accessFocusedChild.isAccessibilityFocused()
&& accessibilityFocusPosition != INVALID_POSITION) {
// Bound the position within the visible children.
final int position = MathUtils.constrain(
accessibilityFocusPosition - mFirstPosition, , getChildCount() - );
final View restoreView = getChildAt(position);
if (restoreView != null) {
restoreView.requestAccessibilityFocus();
}
}
}
if (focusedChild != null) {
focusedChild.setHasTransientState(false);
}
mLayoutMode = LAYOUT_NORMAL;
mDataChanged = false;
if (mPositionScrollAfterLayout != null) {
post(mPositionScrollAfterLayout);
mPositionScrollAfterLayout = null;
}
mNeedSync = false;
setNextSelectedPositionInt(mSelectedPosition);
updateScrollIndicators();
if (mItemCount > ) {
checkSelectionChanged();
}
invokeOnItemScrollListener();
} finally {
if (!blockLayoutRequests) {
mBlockLayoutRequests = false;
}
}
}
在上面代码中，我们一眼就看出了报错的地方：
if (mItemCount == ) {
resetList();
invokeOnItemScrollListener();
return;
} else if (mItemCount != mAdapter.getCount()) {
throw new IllegalStateException("The content of the adapter has changed but "
+ "ListView did not receive a notification. Make sure the content of "
+ "your adapter is not modified from a background thread, but only from "
+ "the UI thread. Make sure your adapter calls notifyDataSetChanged() "
+ "when its content changes. [in ListView(" + getId() + ", " + getClass()
+ ") with Adapter(" + mAdapter.getClass() + ")]");
}
原来错误是从这里报处理的，那什么时候会报错呢？我们看看上面的判断条件：
mItemCount != mAdapter.getCount()。
在上面我们说过notifyDataSetChanged干了两件事，其中的第一件事就是给mItemCount赋值。可以回过头去看看mItemCount = getAdapter().getCount();
现在我们应该已经知道了，当我们调用了notifyDataSetChanged之后，说明数据源已经发生了变化，所以它会重新获取到Adapter里面的count赋值给mItemCount,接着就是执行重新布局，如果我们在给mItemCount赋值之后到执行上面的这个判断之间再一次修改了数据源，那么当执行到上面的这个判断的时候，就会出现mAdapter.getCount()获取的count数是新的数据源的count,跟之前存取mItemCount不一致，这样就会抛出这个异常。也就是说当我们mItemCount赋值之后，如果在执行if (mItemCount != mAdapter.getCount())之前又修改了数据源，就会出现异常。
这个异常一般出现的具体场合，参考下面文章：
关于Adapter的The content of the adapter has changed问题分析
ListView/Adapter IllegalStateException
参考文章：
Android ListView工作原理完全解析，带你从源码的角度彻底理解
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