Question

现在花了几天时间研究这个问题，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。所有组都显示为关闭状态，列表将滚动到顶部。

此问题已在Android API演示中显示。如果您已安装它们，请导航至：

观看次数 - ＆gt;可扩展列表 - ＆gt; 2.光标（人物）：启动示例，展开任何组，转动设备，结果显示组处于折叠状态。

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,
            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被调用。但是：恢复状态是没有效果的。

进一步调试，我发现onRestoreInstanceState（）中恢复的 listState 的内容包含一个空数组，而onSaveInstanceState（）中的 listState 包含数据放入outState时的数组。

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提供一个工作示例，并将“工作”恢复为展开/折叠状态吗？

（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）

Answer 1

这可能会引起我们一些较为谨慎的程序员的蔑视，但您是否只是尝试将状态容器设为static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()。[/ p>

使用SimpleCursorTreeAdapter保存和恢复ExpandableListActivity的折叠状态

1 个答案: