我有一个ExpandableListActivity(使用SimpleCursorTreeAdapter),当用户单击一个子元素时,它会启动另一个活动.在新活动中按下后退按钮时,所有列表项目将再次折叠.如何保存ExpandableListActivity的展开状态并重新恢复.
我已经试图实现onSaveInstanceState()和onRestoreInstanceState()这样…
@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.我也试图恢复onCreate()方法的状态,但它也不被调用：
if (savedInstanceState != null) {
Parcelable listState = savedInstanceState.getParcelable("ListState");
getExpandableListView().onRestoreInstanceState(listState);
}
解决方法
不幸的是,当焦点丢失时,扩展状态总是复位,当再次获得焦点onStart()时,onCreate()不被调用.所以我现在的解决方法是手动存储所有展开的项目的ID,并再次在onStart()中展开它们.我实现了一个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;
}
}
也许有人有一个更好的解决方案.
