Listview更新数据时崩溃The content of the adapter has changed but did not receive a notification._the content of the adapter has changed but listvie-优快云博客

本文链接：https://blog.youkuaiyun.com/qiaohonglu/article/details/70176662

说明：在工作中遇到的问题记录下来，欢迎批评和指正～

1、问题

在listView上下拉刷新或者滑动过程中经常碰到这个复现率比较高的崩溃问题

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)]

2、崩溃解释

是说数据源更新了，但是listview没有及时收到通知进行更新。确保adapter内容更新是在主线程。

3、崩溃场景

1、请求数据是在子线程中进行，之后在该线程中对数据源dataList进行更新；

2、通过handler.sendmessage发消息到主线程notifydatachange。【或者数据源更新和notifydatachange都在主线程但不在同一个handler】

4、异常在代码中的体现

在ListView.java layoutChildren()方法中，如下。当mItenCount != mAdapter.getCount时就会异常。

protected void layoutChildren() {
......
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. Make sure your adapter calls notifyDataSetChanged() "
                        + "when its content changes. [in ListView(" + getId() + ", " + getClass()
                        + ") with Adapter(" + mAdapter.getClass() + ")]");
            }
......
}

5、分析原因

 
 为什么mItemCount和adapter.getCount()会不相等？mItemCount什么时候会被赋值，layoutChilren()什么时候会被执行呢？   

 
 mItemCount赋值时机： 

 
 1、ListView.setAdapter方法中有mItemCount = adapte.getCount()   

 
 2、ListView onMeasure中也存在mItemCount = adapte.getCount()，即重绘会重新赋值，例如：notifydatachanged之后会进行重绘。列表滑动结束action_up之后也会重绘。   

 
 layoutChidren()的调用时机：  

 
 1、ListView每次重绘onLayout()方法中会调用layoutChidren(）。比如notyfydatachanged之后都会重新requestlayout。从而调用layoutChildren（）   

 
 2、手势滑动 case MotionEvent.ACTION_MOVE: 中调用。 

private void onTouchMove(MotionEvent ev, MotionEvent vtev) {
    if (mHasPerformedLongPress) {
        // Consume all move events following a successful long press.
        return;
    }

    int pointerIndex = ev.findPointerIndex(mActivePointerId);
    if (pointerIndex == -1) {
        pointerIndex = 0;
        mActivePointerId = ev.getPointerId(pointerIndex);
    }

    if (mDataChanged) {//数据源头更新 mDataChanged会为true
        // Re-sync everything if data has been changed
        // since the scroll operation can query the adapter.
        layoutChildren();
    }
......

 
  那么问题就在于在子线程更新数据源之后（mDataChanged会置为true），由于notifydatachanged在主线程，两个线程之间是存在时间差的，在这个时间差额中如果滑动列表就导致layoutChildren（）被调用，而notifydatachanged还未执行，所以mItemCount和adapter.getCount（数据源个数）不一致而崩溃。 
 