使用subList的ConcurrentModificationException？

Question

我有一个普通的RecyclerView。

我的RecyclerView有一个监听器接口，Activity在该接口上监听。当单击RecyclerView中的项时，将调用"onItemClick()“事件。

当调用此事件时，我需要从RecyclerView中删除接下来的5个项，并将它们添加到一个Map (Map<Integer, List<Object>>)中。如果再次单击RecyclerView中的相同项目，我希望将这5个项目重新添加到RecyclerView中。

下面是我的代码在我的活动中的样子(注意，我删除了所有不相关的代码，比如onCreate()方法等)：

public class MainActivity extends AppCompatActivity implements MyAdapter.MyAdapterListener {

    // The RecyclerView data
    private List<Object> data = new ArrayList<>();

    // The Map to keep track of all removed data
    private Map<Integer, List<Object>> removedData = new HashMap<>();

    private RecyclerView recyclerView;

    private LinearLayoutManager linearLayoutManager;

    private MyAdapter myAdapter;

    @Override
    public void onItemClick(int position) {
        Item item = (Item) data.get(position);

        // Check if the Map key/value pair already exists
        if (removedData.get(item.getId()) != null) {
            // Key/value pair exists, re-add the 5 items into the
            // RecyclerView and remove the key/value pair from the Map

            List<Object> fiveItems = removedData.get(item.getId());

            // Re-add the five items to the RecyclerView
            data.addAll(position, fiveItems);

            // Remove the key/value pair from the Map
            removedData.remove(item.getId());
        } else {
            // Key/value pair doesn't exist, remove the next 5 items
            // from the RecyclerView and add it to the Map

            int start = position + 1;
            int end = position + 5;

            List<Object> fiveItems = data.subList(start, end);

            // Add the five items to the Map
            removedData.put(item.getId(), fiveItems);

            // Remove the items from the RecyclerView
            data.subList(start, end).clear();
        }

        // Notify data set changed
        myAdapter.notifyDataSetChanged();
    }
}

但是，我在data.addAll(position, fiveItems)行上得到了这个错误

06-FATAL EXCEPTION: main
java.util.ConcurrentModificationException
    at java.util.ArrayList$SubList.size(ArrayList.java:1028)
    at java.util.AbstractCollection.toArray(AbstractCollection.java:136)
    at java.util.ArrayList.addAll(ArrayList.java:589)
    at com.my.package.activity.MainActivity.onItemClicked(MainActivity.java:238)
    at com.my.package.adapter.MyAdapter$ViewHolderItem.onClick(MyAdapter.java:235)
    at android.view.View.performClick(View.java:5637)
    at android.view.View$PerformClick.run(View.java:22429)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6119)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

为什么我会得到这个错误？我该如何修复它？

Answer 1

在你的data.addAll(position，fiveItems)方法中，内部使用迭代器a= c.toArray()，它使用迭代器it =；.When()，你将使用迭代器，同时，如果其他一些人改变了相同的列表，那么modCount也会改变，这会导致exception.So，你需要找出负责它的代码。

来自java api的toArray()源代码

Object[] r = new Object[size()];
        Iterator<E> it = iterator();
        for (int i = 0; i < r.length; i++) {
            if (! it.hasNext()) // fewer elements than expected
                return Arrays.copyOf(r, i);
            r[i] = it.next();
        }
        return it.hasNext() ? finishToArray(r, it) : r;