我正在尝试通过使用 a 来异步查询提供CursorLoader程序SimpleCursorTreeAdapter
这是我的Fragment类，它实现了CursorLoader
public class GroupsListFragment extends ExpandableListFragment implements
LoaderManager.LoaderCallbacks<Cursor> {
private final String DEBUG_TAG = getClass().getSimpleName().toString();
private static final String[] CONTACTS_PROJECTION = new String[] {
ContactsContract.Contacts._ID,
ContactsContract.Contacts.DISPLAY_NAME };
private static final String[] GROUPS_SUMMARY_PROJECTION = new String[] {
ContactsContract.Groups.TITLE, ContactsContract.Groups._ID,
ContactsContract.Groups.SUMMARY_COUNT,
ContactsContract.Groups.ACCOUNT_NAME,
ContactsContract.Groups.ACCOUNT_TYPE,
ContactsContract.Groups.DATA_SET };
GroupsAdapter mAdapter;
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
populateContactList();
getLoaderManager().initLoader(-1, null, this);
}
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
// This is called when a new Loader needs to be created.
Log.d(DEBUG_TAG, "onCreateLoader for loader_id " + id);
CursorLoader cl;
if (id != -1) {
// child cursor
Uri contactsUri = ContactsContract.Data.CONTENT_URI;
String selection = "(("
+ ContactsContract.CommonDataKinds.GroupMembership.DISPLAY_NAME
+ " NOTNULL) AND ("
+ ContactsContract.CommonDataKinds.GroupMembership.HAS_PHONE_NUMBER
+ "=1) AND ("
+ ContactsContract.CommonDataKinds.GroupMembership.DISPLAY_NAME
+ " != '') AND ("
+ ContactsContract.CommonDataKinds.GroupMembership.GROUP_ROW_ID
+ " = ? ))";
String sortOrder = ContactsContract.CommonDataKinds.GroupMembership.DISPLAY_NAME
+ " COLLATE LOCALIZED ASC";
String[] selectionArgs = new String[] { String.valueOf(id) };
cl = new CursorLoader(getActivity(), contactsUri,
CONTACTS_PROJECTION, selection, selectionArgs, sortOrder);
} else {
// group cursor
Uri groupsUri = ContactsContract.Groups.CONTENT_SUMMARY_URI;
String selection = "((" + ContactsContract.Groups.TITLE
+ " NOTNULL) AND (" + ContactsContract.Groups.TITLE
+ " != '' ))";
String sortOrder = ContactsContract.Groups.TITLE
+ " COLLATE LOCALIZED ASC";
cl = new CursorLoader(getActivity(), groupsUri,
GROUPS_SUMMARY_PROJECTION, selection, null, sortOrder);
}
return cl;
}
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
// Swap the new cursor in.
int id = loader.getId();
Log.d(DEBUG_TAG, "onLoadFinished() for loader_id " + id);
if (id != -1) {
// child cursor
if (!data.isClosed()) {
Log.d(DEBUG_TAG, "data.getCount() " + data.getCount());
try {
mAdapter.setChildrenCursor(id, data);
} catch (NullPointerException e) {
Log.w("DEBUG","Adapter expired, try again on the next query: "
+ e.getMessage());
}
}
} else {
mAdapter.setGroupCursor(data);
}
}
public void onLoaderReset(Loader<Cursor> loader) {
// This is called when the last Cursor provided to onLoadFinished()
// is about to be closed.
int id = loader.getId();
Log.d(DEBUG_TAG, "onLoaderReset() for loader_id " + id);
if (id != -1) {
// child cursor
try {
mAdapter.setChildrenCursor(id, null);
} catch (NullPointerException e) {
Log.w("TAG", "Adapter expired, try again on the next query: "
+ e.getMessage());
}
} else {
mAdapter.setGroupCursor(null);
}
}
/**
* Populate the contact list
*/
private void populateContactList() {
// Set up our adapter
mAdapter = new GroupsAdapter(getActivity(),this,
android.R.layout.simple_expandable_list_item_1,
android.R.layout.simple_expandable_list_item_1,
new String[] { ContactsContract.Groups.TITLE }, // Name for group layouts
new int[] { android.R.id.text1 },
new String[] { ContactsContract.Contacts.DISPLAY_NAME }, // Name for child layouts
new int[] { android.R.id.text1 });
setListAdapter(mAdapter);
}
}
这是我的子类的适配器SimpleCursorTreeAdapter
public class GroupsAdapter extends SimpleCursorTreeAdapter {
private final String DEBUG_TAG = getClass().getSimpleName().toString();
private ContactManager mActivity;
private GroupsListFragment mFragment;
// Note that the constructor does not take a Cursor. This is done to avoid
// querying the database on the main thread.
public GroupsAdapter(Context context, GroupsListFragment glf,
int groupLayout, int childLayout, String[] groupFrom,
int[] groupTo, String[] childrenFrom, int[] childrenTo) {
super(context, null, groupLayout, groupFrom, groupTo, childLayout,
childrenFrom, childrenTo);
mActivity = (ContactManager) context;
mFragment = glf;
}
@Override
protected Cursor getChildrenCursor(Cursor groupCursor) {
// Given the group, we return a cursor for all the children within that group
int groupId = groupCursor.getInt(groupCursor
.getColumnIndex(ContactsContract.Groups._ID));
Log.d(DEBUG_TAG, "getChildrenCursor() for groupId " + groupId);
Loader loader = mActivity.getLoaderManager().getLoader(groupId);
if ( loader != null && loader.isReset() ) {
mActivity.getLoaderManager().restartLoader(groupId, null, mFragment);
} else {
mActivity.getLoaderManager().initLoader(groupId, null, mFragment);
}
}
}
问题是，当我单击父组之一时，三件事中的一件会以一种不一致的方式发生。
1）要么组打开，孩子们出现在它下面
2) 组没有打开并且setChildrenCursor()调用抛出一个NullPointerException错误，该错误在 try catch 块中被捕获
3）组不开，不报错
以下是扩展组并显示子项的场景中的一些调试输出：
当显示所有组时，它会输出：
05-20 10:08:22.765: D/GroupsListFragment(22132): onCreateLoader for loader_id -1
05-20 10:08:23.613: D/GroupsListFragment(22132): onLoadFinished() for loader_id -1
-1 是组游标的loader_id
然后，如果我特别选择一个组（我们称之为 A 组），它会输出：
05-20 23:22:31.140: D/GroupsAdapter(13844): getChildrenCursor() for groupId 67
05-20 23:22:31.140: D/GroupsListFragment(13844): onCreateLoader for loader_id 67
05-20 23:22:31.254: D/GroupsListFragment(13844): onLoadFinished() for loader_id 67
05-20 23:22:31.254: D/GroupsListFragment(13844): data.getCount() 4
05-20 23:22:31.254: W/GroupsListFragment(13844): Adapter expired, try again on the next query: null
小组没有扩大，NullPointerException被抓住了。然后，如果我选择另一个组（我们称之为 B 组），它会输出：
05-20 23:25:38.089: D/GroupsAdapter(13844): getChildrenCursor() for groupId 3
05-20 23:25:38.089: D/GroupsListFragment(13844): onCreateLoader for loader_id 3
05-20 23:25:38.207: D/GroupsListFragment(13844): onLoadFinished() for loader_id 3
05-20 23:25:38.207: D/GroupsListFragment(13844): data.getCount() 6
这一次，NullPointerException没有抛出。而不是 B 组扩展，A 组被扩展。
任何人都可以解释setChildrenCursor()呼叫所表现出的行为吗？
我认为组/子 CursorLoaders 如何在onCreateLoader(). 对于该组CursorLoader，我只想要手机中的所有组。子级CursorLoader应包含组内的所有联系人。有谁知道可能是什么问题？
更新
感谢@Yam 的建议，我现在修改了getChildrenCursor()方法。我现在选择 groupCursor 位置而不是 ContactsContract.Groups._ID 的值来传递给 initLoader() 调用。我还将逻辑更改为仅在 loader 不为 null 且 loader isReset 为 false 时调用 restartLoader() 。
protected Cursor getChildrenCursor(Cursor groupCursor) {
// Given the group, we return a cursor for all the children within that
// group
int groupPos = groupCursor.getPosition();
Log.d(DEBUG_TAG, "getChildrenCursor() for groupPos " + groupPos);
Loader loader = mActivity.getLoaderManager().getLoader(groupPos);
if (loader != null && !loader.isReset()) {
mActivity.getLoaderManager().restartLoader(groupPos, null, mFragment);
} else {
mActivity.getLoaderManager().initLoader(groupPos, null, mFragment);
}
return null;
}
这绝对更有意义，并且不会表现出有时而不是其他时间扩展组的一些不稳定行为。
但是，有些联系人显示在他们不属于的组下。还有一些组中确实有联系人，但不会显示任何联系人。所以现在看来getChildrenCursor()问题可能已经解决了。
但是现在看起来是如何在onCreateLoader()方法中实例化 CursorLoaders 的问题。子游标的方法中 的CursorLoader返回是否被不正确地实例化？onCreateLoader()
更新
所以我已经确定了我的问题之一。在该getChildrenCursor()方法中，如果我将 groupId 传递给该initLoader()方法，那么在该onCreateLoader()方法中，当CursorLoader创建它时，它将获得查询的正确 groupid 参数。但是，在onLoadFinished()调用中setChildrenCursor()传递的是第一个参数的加载程序 ID，而不是 groupPosition。我猜我必须将加载器 ID 映射到某些数据结构中的组位置。但我不确定这是否是最好的方法。有没有人有什么建议？