我有一个ExpandableListActivity（使用SimpleCursorTreeAdapter），当用户点击子元素时，它会启动另一个活动。在新活动中按后退按钮时，所有列表项将再次折叠。如何保存ExpandableListActivity的展开状态并再次还原它。
我已经尝试像这样实现onSaveInstanceState（）和onRestoreInstanceState（）......
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Parcelable listState = getExpandableListView().onSaveInstanceState();
outState.putParcelable("ListState", listState);
}
@Override
protected void onRestoreInstanceState(Bundle state) {
super.onRestoreInstanceState(state);
Parcelable listState = state.getParcelable("ListState");
getExpandableListView().onRestoreInstanceState(listState);
}
...但是onRestoreInstanceState（）从未被调用过。我还尝试在onCreate（）方法中恢复状态，但它也没有被调用：
if (savedInstanceState != null) {
Parcelable listState = savedInstanceState.getParcelable("ListState");
getExpandableListView().onRestoreInstanceState(listState);
}
不幸的是，只要焦点丢失，扩展状态总是重置，并且当再次获得焦点但onStart（）时不调用onCreate（）。所以我现在的解决方法是手动存储所有扩展项的ID，并再次在onStart（）中展开它们。我实现了ExpandableListActivity的子类来重用该行为。
public class PersistentExpandableListActivity extends ExpandableListActivity {
private long[] expandedIds;
@Override
protected void onStart() {
super.onStart();
if (this.expandedIds != null) {
restoreExpandedState(expandedIds);
}
}
@Override
protected void onStop() {
super.onStop();
expandedIds = getExpandedIds();
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
this.expandedIds = getExpandedIds();
outState.putLongArray("ExpandedIds", this.expandedIds);
}
@Override
protected void onRestoreInstanceState(Bundle state) {
super.onRestoreInstanceState(state);
long[] expandedIds = state.getLongArray("ExpandedIds");
if (expandedIds != null) {
restoreExpandedState(expandedIds);
}
}
private long[] getExpandedIds() {
ExpandableListView list = getExpandableListView();
ExpandableListAdapter adapter = getExpandableListAdapter();
if (adapter != null) {
int length = adapter.getGroupCount();
ArrayList<Long> expandedIds = new ArrayList<Long>();
for(int i=0; i < length; i++) {
if(list.isGroupExpanded(i)) {
expandedIds.add(adapter.getGroupId(i));
}
}
return toLongArray(expandedIds);
} else {
return null;
}
}
private void restoreExpandedState(long[] expandedIds) {
this.expandedIds = expandedIds;
if (expandedIds != null) {
ExpandableListView list = getExpandableListView();
ExpandableListAdapter adapter = getExpandableListAdapter();
if (adapter != null) {
for (int i=0; i<adapter.getGroupCount(); i++) {
long id = adapter.getGroupId(i);
if (inArray(expandedIds, id)) list.expandGroup(i);
}
}
}
}
private static boolean inArray(long[] array, long element) {
for (long l : array) {
if (l == element) {
return true;
}
}
return false;
}
private static long[] toLongArray(List<Long> list) {
long[] ret = new long[list.size()];
int i = 0;
for (Long e : list)
ret[i++] = e.longValue();
return ret;
}
}
也许某人有更好的解决方案。
这应该工作
Parcelable state = exercisesList.onSaveInstanceState();
exercisesList.setAdapter(....);
exercisesList.onRestoreInstanceState(state);
尝试这个。它将部分地解决问题
yourlist.setSaveEnabled(true);