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/*
* Copyright (C) 2010 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.content;
import android.database.ContentObserver;
import android.os.Handler;
/**
* An abstract class that performs asynchronous loading of data. While Loaders are active
* they should monitor the source of their data and deliver new results when the contents
* change.
*
* @param <D> The result returned when the load is complete
*/
public abstract class Loader<D> {
int mId;
OnLoadCompleteListener<D> mListener;
Context mContext;
public final class ForceLoadContentObserver extends ContentObserver {
public ForceLoadContentObserver() {
super(new Handler());
}
@Override
public boolean deliverSelfNotifications() {
return true;
}
@Override
public void onChange(boolean selfChange) {
forceLoad();
}
}
public interface OnLoadCompleteListener<D> {
/**
* Called on the thread that created the Loader when the load is complete.
*
* @param loader the loader that completed the load
* @param data the result of the load
*/
public void onLoadComplete(Loader<D> loader, D data);
}
/**
* Stores away the application context associated with context. Since Loaders can be used
* across multiple activities it's dangerous to store the context directly.
*
* @param context used to retrieve the application context.
*/
public Loader(Context context) {
mContext = context.getApplicationContext();
}
/**
* Sends the result of the load to the registered listener. Should only be called by subclasses.
*
* Must be called from the UI thread.
*
* @param data the result of the load
*/
public void deliverResult(D data) {
if (mListener != null) {
mListener.onLoadComplete(this, data);
}
}
/**
* @return an application context retrieved from the Context passed to the constructor.
*/
public Context getContext() {
return mContext;
}
/**
* @return the ID of this loader
*/
public int getId() {
return mId;
}
/**
* Registers a class that will receive callbacks when a load is complete. The callbacks will
* be called on the UI thread so it's safe to pass the results to widgets.
*
* Must be called from the UI thread
*/
public void registerListener(int id, OnLoadCompleteListener<D> listener) {
if (mListener != null) {
throw new IllegalStateException("There is already a listener registered");
}
mListener = listener;
mId = id;
}
/**
* Must be called from the UI thread
*/
public void unregisterListener(OnLoadCompleteListener<D> listener) {
if (mListener == null) {
throw new IllegalStateException("No listener register");
}
if (mListener != listener) {
throw new IllegalArgumentException("Attempting to unregister the wrong listener");
}
mListener = null;
}
/**
* Starts an asynchronous load of the contacts list data. When the result is ready the callbacks
* will be called on the UI thread. If a previous load has been completed and is still valid
* the result may be passed to the callbacks immediately. The loader will monitor the source of
* the data set and may deliver future callbacks if the source changes. Calling
* {@link #stopLoading} will stop the delivery of callbacks.
*
* Must be called from the UI thread
*/
public abstract void startLoading();
/**
* Force an asynchronous load. Unlike {@link #startLoading()} this will ignore a previously
* loaded data set and load a new one.
*/
public abstract void forceLoad();
/**
* Stops delivery of updates until the next time {@link #startLoading()} is called
*
* Must be called from the UI thread
*/
public abstract void stopLoading();
/**
* Destroys the loader and frees its resources, making it unusable.
*
* Must be called from the UI thread
*/
public abstract void destroy();
}
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