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关于Adapter的The content of the adapter has changed问题分析

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[摘要]本文是对Adapter的The content of the adapter has changed问题分析的讲解,对学习Android编程技术有所帮助,与大家分享。

关于Adapter的The content of the adapter has changed问题分析

1、问题描述

 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、复现场景

使用ListView和Adapter实现动态增删数据列表功能,初始化数据分为两部分:本地和网络。所以在Adapter的数据初始化的时候,先讲本地数据添加到了容器内。同时发起网络请求,等加载完毕后追加到容器内。
问题出现在:当网络请求完毕后追加数据的时候,抛出上述异常。

3、原因分析

Exception解读:
Adapter的数据内容已经改变,但是ListView却未接收到通知。要确保不在后台线程中修改Adapter的数据内容,而要在UI Thread中修改。确保Adapter的数据内容改变时一定要调用notifyDataSetChanged()方法。
且不管Exception内容,先查询Android源码看看该Exception是从哪里抛出来的。
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,当ListView缓存的数据Count和ListView中Adapter.getCount()不等时,会抛出该异常。
结合开头的异常解读,可以断定肯定是Adapter数据动态更新的问题。仔细检查了自己的代码:
当网络请求完毕后,直接在网络线程(非UI线程)里调用了在Adapter中新增的自定义方法addData(List)更新数据,而addData(List)方法内更新换完数据后,通过Handler发送Message的策略调用Adapter的notifyDataSetChanged()方法通知更新。
这么一来,并不能保证Adapter的数据更新时,立马调用notifyDataSetChanged()通知ListView,这两个线程之间的时间差引起的数据不同步,导致ListView的layoutChildren()中访问Adapter的getCount()方法时,Adapter内已经是最新数据源,而ListView内的缓存数据Count仍是旧数据的Count,该问题最终原因终于浮出水面。

4、解决方案

在本例中,解决方案是:把addData(List)方法内更新数据的代码挪出来,和notifyDataSetChanged()方法一同放在Handler里,保证数据更新时及时通知ListView。
为了尽量避免该问题,以后编程尽量从如下几个方面检查自己的代码:
  • 确保Adapter的数据更新后一定要调用notifyDataSetChanged()方法通知ListView
  • 数据更新和notifyDataSetChanged()放在UI线程内,且必须同步顺序执行,不可异步
  • 仔细检查确认getCount()方法返回值是否正确


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