问题：更改设备(Samsung Galaxy S)的方向时,不会保留和恢复组的展开状态.所有组都显示为已关闭,列表将滚动到顶部.

Android API演示中已经出现此问题.如果您安装了它们,请导航至：

意见 – >可扩展列表 – > 2.光标(人物)：启动示例,展开任何组,转动设备,结果显示处于折叠状态的组.

在下面的代码中,我做了以下操作：从API演示(ExpandableList2.java)中获取代码,并使用onSaveInstantState(),onRestoreInstanceState()和onResume()的实现扩展它.这些方法的实现取自另一个讨论主题(How to preserve scroll position in an ExpandableListView).

import android.app.ExpandableListActivity;
import android.content.AsyncQueryHandler;
import android.content.ContentUris; 
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.os.Parcelable;
import android.provider.ContactsContract.CommonDataKinds.Phone;
import android.provider.ContactsContract.Contacts;
import android.view.View;
import android.widget.CursorTreeAdapter;
import android.widget.ExpandableListView;
import android.widget.SimpleCursorTreeAdapter;

public class MainActivity extends ExpandableListActivity {

private static final String LIST_STATE_KEY = "levelSelectListState";
private static final String LIST_POSITION_KEY = "levelSelectListPosition";
private static final String ITEM_POSITION_KEY = "levelSelectItemPosition";

private static final String[] CONTACTS_PROJECTION = new String[] {
        Contacts._ID,Contacts.DISPLAY_NAME };
private static final int GROUP_ID_COLUMN_INDEX = 0;

private static final String[] PHONE_NUMBER_PROJECTION = new String[] {
        Phone._ID,Phone.NUMBER };

private static final int TOKEN_GROUP = 0;
private static final int TOKEN_CHILD = 1;

private static final class QueryHandler extends AsyncQueryHandler {
    private CursorTreeAdapter mAdapter;

    public QueryHandler(Context context,CursorTreeAdapter adapter) {
        super(context.getContentResolver());
        this.mAdapter = adapter;
    }

    @Override
    protected void onQueryComplete(int token,Object cookie,Cursor cursor) {
        switch (token) {
        case TOKEN_GROUP:
            mAdapter.setGroupCursor(cursor);
            break;

        case TOKEN_CHILD:
            int groupPosition = (Integer) cookie;
            mAdapter.setChildrenCursor(groupPosition,cursor);
            break;
        }
    }
}

public class MyExpandableListAdapter extends SimpleCursorTreeAdapter {

    // Note that the constructor does not take a Cursor. This is done to
    // avoid querying the
    // database on the main thread.
    public MyExpandableListAdapter(Context context,int groupLayout,int childLayout,String[] groupFrom,int[] groupTo,String[] childrenFrom,int[] childrenTo) {

        super(context,null,groupLayout,groupFrom,groupTo,childLayout,childrenFrom,childrenTo);
    }

    @Override
    protected Cursor getChildrenCursor(Cursor groupCursor) {
        // Given the group,we return a cursor for all the children within
        // that group

        // Return a cursor that points to this contact's phone numbers
        Uri.Builder builder = Contacts.CONTENT_URI.buildUpon();
        ContentUris.appendId(builder,groupCursor.getLong(GROUP_ID_COLUMN_INDEX));
        builder.appendEncodedPath(Contacts.Data.CONTENT_DIRECTORY);
        Uri phoneNumbersUri = builder.build();

        mQueryHandler.startQuery(TOKEN_CHILD,groupCursor.getPosition(),phoneNumbersUri,PHONE_NUMBER_PROJECTION,Phone.MIMETYPE
                        + "=?",new String[] { Phone.CONTENT_ITEM_TYPE },null);

        return null;
    }
}

private QueryHandler mQueryHandler;
private CursorTreeAdapter mAdapter;
private Parcelable listState;
private int listPosition;
private int itemPosition;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Set up our adapter
    mAdapter = new MyExpandableListAdapter(
            this,android.R.layout.simple_expandable_list_item_1,new String[] { Contacts.DISPLAY_NAME },// Name for group
                                                    // layouts
            new int[] { android.R.id.text1 },new String[] { Phone.NUMBER },// Number for child layouts
            new int[] { android.R.id.text1 });

    setListAdapter(mAdapter);

    mQueryHandler = new QueryHandler(this,mAdapter);

    // Query for people
    mQueryHandler.startQuery(TOKEN_GROUP,Contacts.CONTENT_URI,CONTACTS_PROJECTION,Contacts.HAS_PHONE_NUMBER + "=1",null);
}

@Override
protected void onDestroy() {
    super.onDestroy();

    // Null out the group cursor. This will cause the group cursor and all
    // of the child cursors
    // to be closed.
    mAdapter.changeCursor(null);
    mAdapter = null;
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    ExpandableListView listView = this.getExpandableListView();
    listState = listView.onSaveInstanceState();
    outState.putParcelable(LIST_STATE_KEY,listState);

    listPosition = listView.getFirstVisiblePosition();
    outState.putInt(LIST_POSITION_KEY,listPosition);

    View itemView = listView.getChildAt(0);
    itemPosition = itemView == null ? 0 : itemView.getTop();
    outState.putInt(ITEM_POSITION_KEY,itemPosition);
}

@Override
protected void onRestoreInstanceState(Bundle state) {
    super.onRestoreInstanceState(state);

    listState = state.getParcelable(LIST_STATE_KEY);
    listPosition = state.getInt(LIST_POSITION_KEY);
    itemPosition = state.getInt(ITEM_POSITION_KEY);
}

@Override
protected void onResume() {
    super.onResume();

    ExpandableListView listView = this.getExpandableListView();
    if (listView != null) {
        if (listState != null) {
            // yes,this code is reached
            listView.onRestoreInstanceState(listState);
            listView.setSelectionFromTop(listPosition,itemPosition);
        }
    }
}
}

使用我确定的调试器,当设备方向改变时,所有这些方法实际上都以正确的顺序调用.但是：恢复状态是没有效果的.

进一步调试它,我发现onRestoreInstanceState()中恢复的listState的内容包含一个空数组,而onSaveInstanceState()中的listState在放入outState时包含其数组中的数据.

所以我的假设是,系统没有正确保存或检索listState Parcelable ……

任何人都可以指出出现了什么问题,或者使用SimpleCursorTreeAdapter和扩展/折叠状态的“工作”恢复提供一个工作示例吗？

(注意：要使用上面的活动代码重现此问题,您需要提供android.permission.READ_CONTACTS权限)