问题
I am trying to implement AlphabetIndexer with Custom Adapter like this
AlphabetIndexer with Custom Adapter
My class ContactsCursorAdapter extends SimpleCursorAdapter and implements SectionIndexer
and I am using a LoaderManager to manage my adapter\'s cursor so i have overridden the swapCursor() method like the second answer to the example above indicates.
public class ContactsCursorAdapter extends SimpleCursorAdapter
implements SectionIndexer{
private LayoutInflater mInflater;
private Context mContext;
private AlphabetIndexer mAlphaIndexer;
public ContactsCursorAdapter(Context context, int layout, Cursor c,
String[] from, int[] to) {
super(context, layout, c, from, to);
mInflater = LayoutInflater.from(context);
mContext = context;
}
public View getView(final int position, View convertView, ViewGroup parent) {
...
}
@Override
public int getPositionForSection(int section) {
return mAlphaIndexer.getPositionForSection(section);
}
@Override
public int getSectionForPosition(int position) {
return mAlphaIndexer.getSectionForPosition(position);
}
@Override
public Object[] getSections() {
return mAlphaIndexer.getSections();
}
public Cursor swapCursor(Cursor c) {
// Create our indexer
if (c != null) {
mAlphaIndexer = new AlphabetIndexer(c, c.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME),
\" ABCDEFGHIJKLMNOPQRSTUVWXYZ\");
}
return super.swapCursor(c);
}
}
However, this errors out if I set my listview to fastScrollEnabled = true
getListView().setFastScrollEnabled(true);
in my class ContactsCursorLoaderListFragment which extends ListFragment and implements LoaderManager.LoaderCallbacks .
Here is the stack trace:
04-25 01:37:23.280: E/AndroidRuntime(711): FATAL EXCEPTION: main
04-25 01:37:23.280: E/AndroidRuntime(711): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sendit/com.sendit.ContactManager}: java.lang.NullPointerException
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.access$600(ActivityThread.java:123)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.os.Handler.dispatchMessage(Handler.java:99)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.os.Looper.loop(Looper.java:137)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.main(ActivityThread.java:4424)
04-25 01:37:23.280: E/AndroidRuntime(711): at java.lang.reflect.Method.invokeNative(Native Method)
04-25 01:37:23.280: E/AndroidRuntime(711): at java.lang.reflect.Method.invoke(Method.java:511)
04-25 01:37:23.280: E/AndroidRuntime(711): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
04-25 01:37:23.280: E/AndroidRuntime(711): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
04-25 01:37:23.280: E/AndroidRuntime(711): at dalvik.system.NativeStart.main(Native Method)
04-25 01:37:23.280: E/AndroidRuntime(711): Caused by: java.lang.NullPointerException
04-25 01:37:23.280: E/AndroidRuntime(711): at com.sendit.ContactsCursorAdapter.getSections(ContactsCursorAdapter.java:222)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.FastScroller.getSectionsFromIndexer(FastScroller.java:507)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.FastScroller.init(FastScroller.java:269)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.FastScroller.<init>(FastScroller.java:155)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.widget.AbsListView.setFastScrollEnabled(AbsListView.java:1144)
04-25 01:37:23.280: E/AndroidRuntime(711): at com.sendit.LoaderCursor$ContactsCursorLoaderListFragment.onActivityCreated(LoaderCursor.java:107)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:847)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1032)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.BackStackRecord.run(BackStackRecord.java:622)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1382)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.Activity.performStart(Activity.java:4474)
04-25 01:37:23.280: E/AndroidRuntime(711): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1929)
04-25 01:37:23.280: E/AndroidRuntime(711): ... 11 more
after the setFastScrollEnabled() method gets called it calls the custom adapter\'s getSections() method which is where it crashes.
public class LoaderCursor extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fm = getFragmentManager();
// Create the list fragment and add it as our sole content.
if (fm.findFragmentById(android.R.id.content) == null) {
ContactsCursorLoaderListFragment list = new ContactsCursorLoaderListFragment();
fm.beginTransaction().add(android.R.id.content, list).commit();
}
}
public static class ContactsCursorLoaderListFragment extends ListFragment
implements LoaderManager.LoaderCallbacks<Cursor> {
ContactsCursorAdapter mAdapter;
Cursor mCursor;
String mCurFilter;
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
populateContactList();
// Prepare the loader. Either re-connect with an existing one,
// or start a new one.
getLoaderManager().initLoader(0, null, this);
ListView lv = getListView();
lv.setFastScrollEnabled(true);
//lv.setScrollingCacheEnabled(true);
lv.setDivider(getResources().getDrawable(R.drawable.list_divider));
}
// These are the Contacts rows that we will retrieve.
final String[] CONTACTS_SUMMARY_PROJECTION = new String[] {
ContactsContract.Contacts._ID,
ContactsContract.Contacts.DISPLAY_NAME,
ContactsContract.Contacts.PHOTO_ID, };
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
// This is called when a new Loader needs to be created. This
// sample only has one Loader, so we don\'t care about the ID.
// First, pick the base URI to use depending on whether we are
// currently filtering.
Uri baseUri;
if (mCurFilter != null) {
baseUri = Uri.withAppendedPath(ContactsContract.Contacts.CONTENT_FILTER_URI,Uri.encode(mCurFilter));
} else {
baseUri = ContactsContract.Contacts.CONTENT_URI;
}
// Now create and return a CursorLoader that will take care of
// creating a Cursor for the data being displayed.
String selection = \"((\" + ContactsContract.Contacts.DISPLAY_NAME +
\" NOTNULL) AND (\" + ContactsContract.Contacts.HAS_PHONE_NUMBER + \"=1)
AND (\" + ContactsContract.Contacts.DISPLAY_NAME + \" != \'\' ))\";
String sortOrder = ContactsContract.Contacts.DISPLAY_NAME
+ \" COLLATE LOCALIZED ASC\";
return new CursorLoader(getActivity(), baseUri,
CONTACTS_SUMMARY_PROJECTION, selection, null, sortOrder);
}
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
// Swap the new cursor in. (The framework will take care of closing the
// old cursor once we return.)
mAdapter.swapCursor(data);
}
public void onLoaderReset(Loader<Cursor> loader) {
// This is called when the last Cursor provided to onLoadFinished()
// above is about to be closed. We need to make sure we are no
// longer using it.
mAdapter.swapCursor(null);
}
/**
* Populate the contact list
*/
private void populateContactList() {
// start mappings
String[] from = new String[] { ContactsContract.Contacts.DISPLAY_NAME };
int[] to = new int[] { R.id.contactInfo };
// Create an empty adapter we will use to display the loaded data.
mAdapter = new ContactsCursorAdapter(getActivity().getApplicationContext(),
R.layout.contact_manager, null, from, to);
setListAdapter(mAdapter);
}
}
}
And if I comment the setFastScrollEnabled() call, then it does not error out, but I do not see the AlphabetIndexer working.
Does this need to be implemented differently because my custom adapter is set in a ListFragment and not a ListActivity?
Does anyone have suggestions about how to make this all work?
回答1:
So I finally got this to work. Here's how i did it:
I added:
ListView lv = getListView();
lv.setFastScrollEnabled(true);
lv.setScrollingCacheEnabled(true);
to the onLoadFinished() method after the new cursor was swapped in like so
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
// Swap the new cursor in. (The framework will take care of closing the
// old cursor once we return.)
mAdapter.swapCursor(data);
ListView lv = getListView();
lv.setFastScrollEnabled(true);
lv.setScrollingCacheEnabled(true);
}
consequently these three statements were removed from the onActivityCreated() method of my custom ListFragment.
来源：https://stackoverflow.com/questions/10224233/alphabetindexer-with-custom-adapter-managed-by-loadermanager