How do I add contact to a group on Android?

I read about ContactsContract.CommonDataKinds.GroupMembership, but I can't figure out what URI use to insert to.

I have prepared this method:

public static Uri addToGroup(ContentResolver resolver, long personId,
            long groupId) {

        ContentValues values = new ContentValues();

        values.put(ContactsContract.CommonDataKinds.GroupMembership.CONTACT_ID, personId);

        values.put(ContactsContract.CommonDataKinds.GroupMembership.GROUP_ROW_ID, groupId);

        return resolver.insert(uri, values);//URI is not known

    }

Can someone tell me what U开发者_C百科RI to use in SDK 2.0+?

I found the resolution and I post it here:

public Uri addToGroup(long personId, long groupId) {

    //remove if exists
    this.removeFromGroup(personId, groupId);

    ContentValues values = new ContentValues();
    values.put(ContactsContract.CommonDataKinds.GroupMembership.RAW_CONTACT_ID,
            personId);
    values.put(
            ContactsContract.CommonDataKinds.GroupMembership.GROUP_ROW_ID,
            groupId);
    values
            .put(
                    ContactsContract.CommonDataKinds.GroupMembership.MIMETYPE,
                    ContactsContract.CommonDataKinds.GroupMembership.CONTENT_ITEM_TYPE);

    return this.ctx.getContentResolver().insert(
            ContactsContract.Data.CONTENT_URI, values);

}

But I don't get something, why do I have to use RAW_CONTACT_ID and not CONTACT_ID, the later raises nullpointerexception.