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/*
* 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 final Object mLock = new Object();
private Transport mTransport; // guarded by mLock
Handler mHandler;
/**
* Creates a content observer.
*
* @param handler The handler to run {@link #onChange} on, or null if none.
*/
public ContentObserver(Handler handler) {
mHandler = handler;
}
/**
* Gets access to the binder transport object. Not for public consumption.
*
* {@hide}
*/
public IContentObserver getContentObserver() {
synchronized (mLock) {
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 (mLock) {
final Transport oldTransport = mTransport;
if (oldTransport != null) {
oldTransport.releaseContentObserver();
mTransport = null;
}
return oldTransport;
}
}
/**
* Returns true if this observer is interested receiving self-change notifications.
*
* Subclasses should override this method to indicate whether the observer
* is interested in receiving notifications for changes that it made to the
* content itself.
*
* @return True if self-change notifications should be delivered to the observer.
*/
public boolean deliverSelfNotifications() {
return false;
}
/**
* This method is called when a content change occurs.
*
* @param selfChange True if this is a self-change notification.
*/
public void onChange(boolean selfChange) {
// Do nothing. Subclass should override.
}
/**
* Dispatches a change notification to the observer.
*
* If a {@link Handler} was supplied to the {@link ContentObserver} constructor,
* then a call to the {@link #onChange} method is posted to the handler's message queue.
* Otherwise, the {@link #onChange} method is invoked immediately on this thread.
*
* @param selfChange True if this is a self-change notification.
*/
public final void dispatchChange(boolean selfChange) {
if (mHandler == null) {
onChange(selfChange);
} else {
mHandler.post(new NotificationRunnable(selfChange));
}
}
private final class NotificationRunnable implements Runnable {
private final boolean mSelf;
public NotificationRunnable(boolean self) {
mSelf = self;
}
@Override
public void run() {
ContentObserver.this.onChange(mSelf);
}
}
private static final class Transport extends IContentObserver.Stub {
private ContentObserver mContentObserver;
public Transport(ContentObserver contentObserver) {
mContentObserver = contentObserver;
}
@Override
public void onChange(boolean selfChange) {
ContentObserver contentObserver = mContentObserver;
if (contentObserver != null) {
contentObserver.dispatchChange(selfChange);
}
}
public void releaseContentObserver() {
mContentObserver = null;
}
}
}
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