為了更好的了解這個問題出現的真正原因，建議首先看看下面兩篇文章：
淺析notifyDataSetChanged内部工作流程
ListView中requestLayout執行流程解析
綜合上面兩篇文章，我們可以把整個執行過程用下圖展示出來。這個圖非常的關鍵，一定要保證在看下文的時候已經了解了上圖的過程。
下面看看錯誤提示。
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)]
這個問題就是當我們調用notifyDataSetChanged()的過程中，資料源可能發生了改變，這樣出現前後資料源不一緻而報錯，可能這樣說還是不好了解，下面我們可以從源碼的角度來進行分析。
從淺析notifyDataSetChanged内部工作流程文章中我們需要理出以下兩點：
當執行notifyDataSetChanged()，它内部做了兩件事情,具體的代碼在AdapterDataSetObserver的onChanged方法裡面：
1、mDataChanged = true;
mOldItemCount = mItemCount;
mItemCount = getAdapter().getCount();
2、requestLayout();
可以看到做完這兩件事情後，它進入了requestLayout()方法中，requestLayout方法中做了什麼事情，這裡就不細說，看看ListView中requestLayout執行流程解析這篇文章應該就知道了，從上圖可以知道，requestLayout内部其實就是執行了performTraversals(),performTraversals()内部執行的就是measure,layout,draw方法，onMeasure()用于測量View的大小，onLayout()用于确定View的布局，onDraw()用于将View繪制到界面上。而在ListView當中，onMeasure()并沒有什麼特殊的地方，因為它終歸是一個View，占用的空間最多并且通常也就是整個螢幕。onDraw()在ListView當中也沒有什麼意義，因為ListView本身并不負責繪制，而是由ListView當中的子元素來進行繪制的。那麼ListView大部分的功能其實都是在onLayout()方法中進行的了,是以我重點關注到onLayout()方法，從圖知道它執行了layoutChildren()方法。
ListView中是沒有onLayout()這個方法的，這是因為這個方法是在ListView的父類AbsListView中實作的,我們來跟跟源碼：
@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);
}
//這個方法是重點
layoutChildren();
mInLayout = false;
mOverscrollMax = (b - t) / OVERSCROLL_LIMIT_DIVISOR;
}
onLayout()方法中并沒有做什麼複雜的邏輯操作，主要就是一個判斷，如果ListView的大小或者位置發生了變化，那麼changed變量就會變成true，此時會要求所有的子布局都強制進行重繪。重點調用了layoutChildren()這個方法，從方法名上我們就可以猜出這個方法是用來進行子元素布局的，不過進入到這個方法當中你會發現這是個空方法，沒有一行代碼。這當然是可以了解的了，因為子元素的布局應該是由具體的實作類來負責完成的，而不是由父類完成。那麼進入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;
}
}
}
在上面代碼中，我們一眼就看出了報錯的地方：
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() + ")]");
}
原來錯誤是從這裡報處理的，那什麼時候會報錯呢？我們看看上面的判斷條件：
mItemCount != mAdapter.getCount()。
在上面我們說過notifyDataSetChanged幹了兩件事，其中的第一件事就是給mItemCount指派。可以回過頭去看看mItemCount = getAdapter().getCount();
現在我們應該已經知道了，當我們調用了notifyDataSetChanged之後，說明資料源已經發生了變化，是以它會重新擷取到Adapter裡面的count指派給mItemCount,接着就是執行重新布局，如果我們在給mItemCount指派之後到執行上面的這個判斷之間再一次修改了資料源，那麼當執行到上面的這個判斷的時候，就會出現mAdapter.getCount()擷取的count數是新的資料源的count,跟之前存取mItemCount不一緻，這樣就會抛出這個異常。也就是說當我們mItemCount指派之後，如果在執行if (mItemCount != mAdapter.getCount())之前又修改了資料源，就會出現異常。
這個異常一般出現的具體場合，參考下面文章：
關于Adapter的The content of the adapter has changed問題分析
ListView/Adapter IllegalStateException
參考文章：
Android ListView工作原理完全解析，帶你從源碼的角度徹底了解
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