android – 使用SimpleCursorTreeAdapter保存和恢复ExpandableListActivity的折叠状态

概述在花了几天研究这个问题后,我终于放弃并发布了这个问题.这里已经回答了类似的问题(部分),并提出了解决方案,但最终没有人帮助我.与讨论的主题和我的问题的区别似乎是：其他人似乎没有使用SimpleCursorTreeAdapter来提供列表…… 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 在花了几天研究这个问题后,我终于放弃并发布了这个问题.这里已经回答了类似的问题(部分),并提出了解决方案,但最终没有人帮助我.与讨论的主题和我的问题的区别似乎是：其他人似乎没有使用SimpleCursorTreeAdapter来提供列表……

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 *** 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;@OverrIDepublic 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);}@OverrIDeprotected 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;}@OverrIDeprotected 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);}@OverrIDeprotected 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);}@OverrIDeprotected 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)

解决方法 这可能会引起我们一些较为谨慎的程序员的蔑视,但你是否只是试图让你的状态容器成为静态对象？但即使在此之前,也许您可​​能会在检索对象后在某处添加notifydatasetchanged(). 总结

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