【原創】關於Adapter的The content of the adapter has changed問題分析

關於Adapter的The content of the adapter has changed問題分析

 

1、問題描述

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)]

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.ListView.layoutChildren(ListView.java:1555)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.AbsListView.onLayout(AbsListView.java:2091)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.FrameLayout.onLayout(FrameLayout.java:388)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1589)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.FrameLayout.onLayout(FrameLayout.java:388)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.widget.FrameLayout.onLayout(FrameLayout.java:388)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.View.layout(View.java:14785)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewGroup.layout(ViewGroup.java:4631)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1985)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1742)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5582)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.Choreographer.doCallbacks(Choreographer.java:562)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.Choreographer.doFrame(Choreographer.java:532)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.os.Handler.handleCallback(Handler.java:733)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.os.Handler.dispatchMessage(Handler.java:95)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.os.Looper.loop(Looper.java:137)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at android.app.ActivityThread.main(ActivityThread.java:4998)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at java.lang.reflect.Method.invokeNative(Native Method)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at java.lang.reflect.Method.invoke(Method.java:515)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)

07-28 17:22:02.162: E/AndroidRuntime(16779):   at dalvik.system.NativeStart.main(Native Method)

07-28 17:22:02.162: W/ActivityManager(588):   Force finishing activity  

 

2、復現場景

使用ListView和Adapter實現動態增刪數據列表功能，初始化數據分為兩部分：本地和網絡。所以在Adapter的數據初始化的時候，先講本地數據添加到了容器內。同時發起網絡請求，等加載完畢后追加到容器內。

問題出現在：當網絡請求完畢后追加數據的時候，拋出上述異常。

 

3、原因分析

Exception解讀：

         Adapter的數據內容已經改變，但是ListView卻未接收到通知。要確保不在后台線程中修改Adapter的數據內容，而要在UI Thread中修改。確保Adapter的數據內容改變時一定要調用notifyDataSetChanged()方法。

 

且不管Exception內容，先查詢Android源碼看看該Exception是從哪里拋出來的。

在ListView的layoutChildren()方法里有如下一段方法：

// Handle the empty set by removing all views that are visible
// and calling it a day
if (mItemCount == 0) {
    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. [in ListView(" + getId() + ", " + getClass()
            + ") with Adapter(" + mAdapter.getClass() + ")]");
}

 

亦即， 當ListView緩存的數據Count和ListView中Adapter.getCount()不等時，會拋出該異常。

 

結合開頭的異常解讀，可以斷定肯定是Adapter數據動態更新的問題。仔細檢查了自己的代碼：

 

當網絡請求完畢后，直接在網絡線程（非UI線程）里調用了在Adapter中新增的自定義方法addData(List)更新數據，而addData(List)方法內更新換完數據后，通過Handler發送Message的策略調用Adapter的notifyDataSetChanged()方法通知更新。

 

這么一來，並不能保證Adapter的數據更新時，立馬調用notifyDataSetChanged()通知ListView，這兩個線程之間的時間差引起的數據不同步，導致ListView的layoutChildren()中訪問Adapter的getCount()方法時，Adapter內已經是最新數據源，而ListView內的緩存數據Count仍是舊數據的Count，該問題最終原因終於浮出水面。

 

4、解決方案

在本例中，解決方案是： 把addData(List)方法內更新數據的代碼挪出來，和notifyDataSetChanged()方法一同放在Handler里，保證數據更新時及時通知ListView。

 

為了盡量避免該問題，以后編程盡量從如下幾個方面檢查自己的代碼：

• 確保Adapter的數據更新后一定要調用notifyDataSetChanged()方法通知ListView
• 數據更新和notifyDataSetChanged()放在UI線程內，且必須同步順序執行，不可異步
• 仔細檢查確認getCount()方法返回值是否正確