在我的应用程序我有ExpandableListActivity派生的类。 当我滚动的内容，然后更换手机的方向或编辑一个项目，然后再返回到列表中，原来的列表中的位置并不preserved。 我已经尝试了两个解决方案，类似于我最近成功地与ListActivity派生类中使用。

in my app I have a class derived from ExpandableListActivity. When I scroll the contents, and then change phone orientation or edit an item and then go back to the list, the original list position is not preserved. I have tried two solutions, similar to those I have recently successfully used with ListActivity-derived classes.

解决方案1：

protected void onRestoreInstanceState(Bundle state) {
    super.onRestoreInstanceState(state);
    mListState = state.getParcelable(LIST_STATE);
}

protected void onResume() {
    super.onResume();
    loadData();
    if (mListState != null)
        getExpandableListView().onRestoreInstanceState(mListState);
}

protected void onSaveInstanceState(Bundle state) {
    super.onSaveInstanceState(state);
    mListState = getExpandableListView().onSaveInstanceState();
    state.putParcelable(LIST_STATE, mListState);
}

解决方案2：

Solution 2:

protected void onRestoreInstanceState(Bundle state) {
    super.onRestoreInstanceState(state);
    mListPosition = state.getInt(LIST_STATE);
}

protected void onResume() {
    super.onResume();
    loadData();
    getExpandableListView().setSelection(mListPosition);
}

protected void onSaveInstanceState(Bundle state) {
    super.onSaveInstanceState(state);
    mListPosition = getExpandableListView().getFirstVisiblePosition();
    state.putInt(LIST_STATE, mListPosition);
}

无论是解决方案的工作。我也尝试了两个解决方案相结合，而这个作品时，我编辑的项目，并返回到列表中，但是当我改变手机方向这是行不通的。

Neither solution works. I have also tried to combine the two solutions, and this works when I edit an item and go back to the list, but it does NOT work when I change the phone orientation

任何人都可以提出来实现我的目标的好方法？

Anyone can suggest a good way to achieve my goal?

推荐答案

经过几次实验，我得出一个满意的解决方案，这也preserves顶部可见项目的精细滚动位置。

After a few experiments I have come to a satisfactory solution, which also preserves the fine scroll position of the top visible item.

由于事实上，三个不同的部分信息需要保存和恢复：列表中的状态（例如哪些群体扩展），第一个可见项目的索引，并以其优良的滚动位置

As a matter of fact, three different pieces of information need to be saved and restored: the list state (e.g. which groups are expanded), the index of the first visible item, and its fine scroll position.

不幸的是，似乎只有第一个被保存由可膨胀列表视图的的onSaveInstanceState方法，所以其他两个需要分开保存。这是一个不可扩展列表视图，它出现的onSaveInstanceState方法，将所有需要正确地恢复状态列表和位置（关于这个问题的信息不同，请参阅的滚动到列表视图的位置）。

Unfortunately, it seems that only the first one is saved by the onSaveInstanceState method of the expandable list view, so the other two need to be saved separately. This is different from a non expandable list view, where it appears the onSaveInstanceState method saves all the information needed to properly restore state and position of the list (on this subject, see Scroll to a position in a listView).

下面是code段;在ExpandableListActivity派生类的顶部：

Here are the code snippets; on top of the ExpandableListActivity-derived class:

private static final String LIST_STATE_KEY = "listState";
private static final String LIST_POSITION_KEY = "listPosition";
private static final String ITEM_POSITION_KEY = "itemPosition";

private Parcelable mListState = null;
private int mListPosition = 0;
private int mItemPosition = 0;

于是，一些覆盖：

Then, some overrides:

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

    // Retrieve list state and list/item positions
    mListState = state.getParcelable(LIST_STATE_KEY);
    mListPosition = state.getInt(LIST_POSITION_KEY);
    mItemPosition = state.getInt(ITEM_POSITION_KEY);
}

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

    // Load data from DB and put it onto the list
    loadData();

    // Restore list state and list/item positions
    ExpandableListView listView = getExpandableListView();
    if (mListState != null)
        listView.onRestoreInstanceState(mListState);
    listView.setSelectionFromTop(mListPosition, mItemPosition);
}

protected void onSaveInstanceState(Bundle state) {
    super.onSaveInstanceState(state);

    // Save list state
    ExpandableListView listView = getExpandableListView();
    mListState = listView.onSaveInstanceState();
    state.putParcelable(LIST_STATE_KEY, mListState);

    // Save position of first visible item
    mListPosition = listView.getFirstVisiblePosition();
    state.putInt(LIST_POSITION_KEY, mListPosition);

    // Save scroll position of item
    View itemView = listView.getChildAt(0);
    mItemPosition = itemView == null ? 0 : itemView.getTop();
    state.putInt(ITEM_POSITION_KEY, mItemPosition);
}

这工作正常，我的升级Froyo设备上。

This works fine on my Froyo device.