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

Question

在花了几天时间研究这个问题之后，我终于放弃并发布了这个问题。这里(部分)回答了类似的问题并提出了解决方案，但没有一个最终帮助了我。与讨论的主题和我的问题的区别似乎是:其他人似乎都没有使用 SimpleCursorTreeAdapter 来提供列表...

问题:当更改我的设备 (Samsung Galaxy S) 的方向时，组的展开状态不会被保留和恢复。所有组都显示为已关闭，列表滚动到顶部。

该问题已在 Android API 演示 中显现。如果您安装了它们，请导航至:

Views --> Expandable Lists --> 2. Cursor (People): 启动示例，展开任何组，转动你的设备，结果显示该组处于折叠状态。

在下面的代码中，我执行了以下操作:从 API 演示 (ExpandableList2.java) 中提取代码并使用 onSaveInstantState()、onRestoreInstanceState() 和 onResume() 的实现对其进行扩展。这些方法的实现取自此处的另一个讨论线程 (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,
            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, null, Contacts.CONTENT_URI,
            CONTACTS_PROJECTION, Contacts.HAS_PHONE_NUMBER + "=1", null,
            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:恢复状态无效。

进一步调试，发现onRestoreInstanceState()中恢复的listState的内容是一个空数组，而onSaveInstanceState()中的listState包含的是数据放入 outState 时的数组。

所以我的假设是，listState Parcelable 没有被系统正确保存或检索...

任何人都可以指出出了什么问题，或者提供一个使用 SimpleCursorTreeAdapter 并“有效”恢复展开/折叠状态的工作示例吗？

(注意:要用上面的activity代码重现这个问题，需要提供android.permission.READ_CONTACTS权限)

Answer 1

这可能会引起我们一些更谨慎的程序员的蔑视，但是您是否只是尝试过让您的状态容器成为一个 static 对象？但即使在那之前，也许您可​​能会受益于在检索对象后的某处添加 notifydatasetchanged()。