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

其中错误描述：

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.

的意思大体是，你的adapter的内容变化了，但是你的ListView并不知情。请保证你adapter的数据在主线程中进行更改！

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

1.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：

[code]1.确保Adapter的数据更新后一定要调用notifyDataSetChanged()方法通知ListView
2.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
3.仔细检查确认getCount()方法返回值是否正确

2.知道了原因，改起来就好办多了，我将我的adapter类改为：

在CODE上查看代码片派生到我的代码片

[code]private class DeviceAdapter extends BaseAdapter {  

    private LayoutInflater inflater;  
    private ArrayList<Device> devices;  

    public DeviceAdapter() {  
        inflater = LayoutInflater.from(mContext);  
    }  

    @SuppressWarnings("unchecked")  
    public void setDeviceList(ArrayList<Device> list) {  
        if (list != null) {  
            devices = (ArrayList<Device>) list.clone();  
            notifyDataSetChanged();  
        }  
    }  

    public void clearDeviceList() {  
        if (devices != null) {  
            devices.clear();  
        }  
        notifyDataSetChanged();  
    }  

    @Override  
    public int getCount() {  
        return devices == null ? 0 : devices.size();  
    }

相对于原来，我做了两项改动：

1.将所有数据“完全”保存在adapter内部，即使有外部数据进入，也会用.clone()重新生成副本，保证了数据完全是由adapter维护的。

2.保证所有setDeviceList()/clearDeviceList()是从主线程里调用的，如何保证是从主线程中调用的呢：

　　a.调用Activity.runOnUIThread()方法；

　　b.使用Handler（其实这并不非常准确，因为Handler也可以运行在非UI线程）；

　　c.使用AsyncTask。