src/com/android/contacts/util/NotifyingAsyncQueryHandler.java

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.contacts.util;

import android.content.AsyncQueryHandler;
import android.content.Context;
import android.database.Cursor;

import java.lang.ref.WeakReference;

/**
 * Slightly more abstract {@link AsyncQueryHandler} that helps keep a
 * {@link WeakReference} back to a listener. Will properly close any
 * {@link Cursor} if the listener ceases to exist.
 * <p>
 * This pattern can be used to perform background queries without leaking
 * {@link Context} objects.
 */
public class NotifyingAsyncQueryHandler extends AsyncQueryHandler {
    private WeakReference<AsyncQueryListener> mListener;

    /**
     * Interface to listen for completed query operations.
     */
    public interface AsyncQueryListener {
        void onQueryComplete(int token, Object cookie, Cursor cursor);
    }

    public NotifyingAsyncQueryHandler(Context context, AsyncQueryListener listener) {
        super(context.getContentResolver());
        setQueryListener(listener);
    }

    /**
     * Assign the given {@link AsyncQueryListener} to receive query events from
     * asynchronous calls. Will replace any existing listener.
     */
    public void setQueryListener(AsyncQueryListener listener) {
        mListener = new WeakReference<AsyncQueryListener>(listener);
    }

    /** {@inheritDoc} */
    @Override
    protected void onQueryComplete(int token, Object cookie, Cursor cursor) {
        final AsyncQueryListener listener = mListener.get();
        if (listener != null) {
            listener.onQueryComplete(token, cookie, cursor);
        } else if (cursor != null) {
            cursor.close();
        }
    }
}