1/*
2 * Copyright (C) 2012 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License
15 */
16
17package com.android.contacts.common.database;
18
19import android.content.AsyncQueryHandler;
20import android.content.ContentResolver;
21import android.database.Cursor;
22import android.net.Uri;
23
24/**
25 * An {@AsyncQueryHandler} that will never return a null cursor.
26 * <p>
27 * Instead, will return a {@link Cursor} with 0 records.
28 */
29public abstract class NoNullCursorAsyncQueryHandler extends AsyncQueryHandler {
30
31    public NoNullCursorAsyncQueryHandler(ContentResolver cr) {
32        super(cr);
33    }
34
35    @Override
36    public void startQuery(int token, Object cookie, Uri uri, String[] projection, String selection,
37            String[] selectionArgs, String orderBy) {
38        final CookieWithProjection projectionCookie = new CookieWithProjection(cookie, projection);
39        super.startQuery(token, projectionCookie, uri, projection, selection, selectionArgs,
40                orderBy);
41    }
42
43    @Override
44    protected final void onQueryComplete(int token, Object cookie, Cursor cursor) {
45        CookieWithProjection projectionCookie = (CookieWithProjection) cookie;
46
47        super.onQueryComplete(token, projectionCookie.originalCookie, cursor);
48
49        if (cursor == null) {
50            cursor = new EmptyCursor(projectionCookie.projection);
51        }
52        onNotNullableQueryComplete(token, projectionCookie.originalCookie, cursor);
53    }
54
55    protected abstract void onNotNullableQueryComplete(int token, Object cookie, Cursor cursor);
56
57    /**
58     * Class to add projection to an existing cookie.
59     */
60    private static class CookieWithProjection {
61        public final Object originalCookie;
62        public final String[] projection;
63
64        public CookieWithProjection(Object cookie, String[] projection) {
65            this.originalCookie = cookie;
66            this.projection = projection;
67        }
68    }
69}
70