android - 如何在 ExpandableListView 中保留滚动位置

Question

在我的应用程序中，我有一个派生自 ExpandableListActivity 的类。当我滚动内容，然后更改手机方向或编辑项目然后返回列表时，原始列表位置不会保留。我尝试了两种解决方案，类似于我最近成功用于 ListActivity 派生类的解决方案。

解决方案一:

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:

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);
}

两种解决方案均无效。我还尝试将这两种解决方案结合起来，当我编辑一个项目并返回列表时这会起作用，但当我更改手机方向时它不起作用

谁能提出实现我目标的好方法？

Answer 1

经过几次实验，我找到了一个令人满意的解决方案，它还保留了顶部可见项目的精细滚动位置。

事实上，需要保存和恢复三种不同的信息:列表状态(例如展开了哪些组)、第一个可见项目的索引及其精细滚动位置。

可惜的是，展开 ListView 的onSaveInstanceState方法好像只保存了第一个，其他两个需要单独保存。这与不可展开的 ListView 不同，其中 onSaveInstanceState 方法似乎保存了正确恢复列表状态和位置所需的所有信息(关于此主题，请参阅 Maintain/Save/Restore scroll position when returning to a ListView)。

这是代码 fragment ；在 ExpandableListActivity 派生类之上:

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;

然后，一些覆盖:

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);
}

这在我的 Froyo 设备上运行良好。