Android example source code file (ContentObserver.java)

This example Android source code file (ContentObserver.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, contentobserver, icontentobserver, notificationrunnable, object, os, transport

The ContentObserver.java Android example source code

/*
 * Copyright (C) 2007 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 android.database;

import android.os.Handler;

/**
 * Receives call backs for changes to content. Must be implemented by objects which are added
 * to a {@link ContentObservable}.
 */
public abstract class ContentObserver {

    private Transport mTransport;

    // Protects mTransport
    private Object lock = new Object();

    /* package */ Handler mHandler;

    private final class NotificationRunnable implements Runnable {

        private boolean mSelf;

        public NotificationRunnable(boolean self) {
            mSelf = self;
        }

        public void run() {
            ContentObserver.this.onChange(mSelf);
        }
    }

    private static final class Transport extends IContentObserver.Stub {
        ContentObserver mContentObserver;

        public Transport(ContentObserver contentObserver) {
            mContentObserver = contentObserver;
        }

        public boolean deliverSelfNotifications() {
            ContentObserver contentObserver = mContentObserver;
            if (contentObserver != null) {
                return contentObserver.deliverSelfNotifications();
            }
            return false;
        }

        public void onChange(boolean selfChange) {
            ContentObserver contentObserver = mContentObserver;
            if (contentObserver != null) {
                contentObserver.dispatchChange(selfChange);
            }
        }

        public void releaseContentObserver() {
            mContentObserver = null;
        }
    }

    /**
     * onChange() will happen on the provider Handler.
     *
     * @param handler The handler to run {@link #onChange} on.
     */
    public ContentObserver(Handler handler) {
        mHandler = handler;
    }

    /**
     * Gets access to the binder transport object. Not for public consumption.
     *
     * {@hide}
     */
    public IContentObserver getContentObserver() {
        synchronized(lock) {
            if (mTransport == null) {
                mTransport = new Transport(this);
            }
            return mTransport;
        }
    }

    /**
     * Gets access to the binder transport object, and unlinks the transport object
     * from the ContentObserver. Not for public consumption.
     *
     * {@hide}
     */
    public IContentObserver releaseContentObserver() {
        synchronized(lock) {
            Transport oldTransport = mTransport;
            if (oldTransport != null) {
                oldTransport.releaseContentObserver();
                mTransport = null;
            }
            return oldTransport;
        }
    }

    /**
     * Returns true if this observer is interested in notifications for changes
     * made through the cursor the observer is registered with.
     */
    public boolean deliverSelfNotifications() {
        return false;
    }

    /**
     * This method is called when a change occurs to the cursor that
     * is being observed.
     *  
     * @param selfChange true if the update was caused by a call to <code>commit on the
     *  cursor that is being observed.
     */
    public void onChange(boolean selfChange) {}

    public final void dispatchChange(boolean selfChange) {
        if (mHandler == null) {
            onChange(selfChange);
        } else {
            mHandler.post(new NotificationRunnable(selfChange));
        }
    }
}