566 lines
21 KiB
Java
566 lines
21 KiB
Java
/*
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* Copyright (C) 2010 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.content;
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import android.database.ContentObserver;
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import android.os.Handler;
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import android.util.DebugUtils;
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import java.io.FileDescriptor;
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import java.io.PrintWriter;
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/**
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* A class that performs asynchronous loading of data. While Loaders are active
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* they should monitor the source of their data and deliver new results when the contents
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* change. See {@link android.app.LoaderManager} for more detail.
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*
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* <p><b>Note on threading:</b> Clients of loaders should as a rule perform
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* any calls on to a Loader from the main thread of their process (that is,
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* the thread the Activity callbacks and other things occur on). Subclasses
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* of Loader (such as {@link AsyncTaskLoader}) will often perform their work
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* in a separate thread, but when delivering their results this too should
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* be done on the main thread.</p>
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*
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* <p>Subclasses generally must implement at least {@link #onStartLoading()},
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* {@link #onStopLoading()}, {@link #onForceLoad()}, and {@link #onReset()}.</p>
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*
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* <p>Most implementations should not derive directly from this class, but
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* instead inherit from {@link AsyncTaskLoader}.</p>
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*
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* <div class="special reference">
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* <h3>Developer Guides</h3>
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* <p>For more information about using loaders, read the
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* <a href="{@docRoot}guide/components/loaders.html">Loaders</a> developer guide.</p>
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* </div>
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*
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* @param <D> The result returned when the load is complete
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*
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* @deprecated Use the <a href="{@docRoot}tools/extras/support-library.html">Support Library</a>
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* {@link androidx.loader.content.Loader}
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*/
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@Deprecated
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public class Loader<D> {
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int mId;
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OnLoadCompleteListener<D> mListener;
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OnLoadCanceledListener<D> mOnLoadCanceledListener;
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Context mContext;
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boolean mStarted = false;
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boolean mAbandoned = false;
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boolean mReset = true;
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boolean mContentChanged = false;
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boolean mProcessingChange = false;
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/**
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* An implementation of a ContentObserver that takes care of connecting
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* it to the Loader to have the loader re-load its data when the observer
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* is told it has changed. You do not normally need to use this yourself;
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* it is used for you by {@link CursorLoader} to take care of executing
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* an update when the cursor's backing data changes.
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*
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* @deprecated Use {@link androidx.loader.content.Loader.ForceLoadContentObserver}
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*/
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@Deprecated
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public final class ForceLoadContentObserver extends ContentObserver {
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public ForceLoadContentObserver() {
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super(new Handler());
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}
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@Override
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public boolean deliverSelfNotifications() {
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return true;
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}
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@Override
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public void onChange(boolean selfChange) {
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onContentChanged();
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}
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}
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/**
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* Interface that is implemented to discover when a Loader has finished
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* loading its data. You do not normally need to implement this yourself;
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* it is used in the implementation of {@link android.app.LoaderManager}
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* to find out when a Loader it is managing has completed so that this can
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* be reported to its client. This interface should only be used if a
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* Loader is not being used in conjunction with LoaderManager.
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*
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* @deprecated Use {@link androidx.loader.content.Loader.OnLoadCompleteListener}
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*/
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@Deprecated
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public interface OnLoadCompleteListener<D> {
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/**
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* Called on the thread that created the Loader when the load is complete.
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*
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* @param loader the loader that completed the load
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* @param data the result of the load
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*/
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public void onLoadComplete(Loader<D> loader, D data);
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}
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/**
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* Interface that is implemented to discover when a Loader has been canceled
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* before it finished loading its data. You do not normally need to implement
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* this yourself; it is used in the implementation of {@link android.app.LoaderManager}
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* to find out when a Loader it is managing has been canceled so that it
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* can schedule the next Loader. This interface should only be used if a
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* Loader is not being used in conjunction with LoaderManager.
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*
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* @deprecated Use {@link androidx.loader.content.Loader.OnLoadCanceledListener}
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*/
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@Deprecated
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public interface OnLoadCanceledListener<D> {
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/**
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* Called on the thread that created the Loader when the load is canceled.
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*
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* @param loader the loader that canceled the load
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*/
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public void onLoadCanceled(Loader<D> loader);
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}
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/**
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* Stores away the application context associated with context.
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* Since Loaders can be used across multiple activities it's dangerous to
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* store the context directly; always use {@link #getContext()} to retrieve
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* the Loader's Context, don't use the constructor argument directly.
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* The Context returned by {@link #getContext} is safe to use across
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* Activity instances.
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*
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* @param context used to retrieve the application context.
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*/
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public Loader(Context context) {
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mContext = context.getApplicationContext();
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}
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/**
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* Sends the result of the load to the registered listener. Should only be called by subclasses.
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*
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* Must be called from the process's main thread.
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*
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* @param data the result of the load
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*/
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public void deliverResult(D data) {
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if (mListener != null) {
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mListener.onLoadComplete(this, data);
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}
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}
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/**
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* Informs the registered {@link OnLoadCanceledListener} that the load has been canceled.
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* Should only be called by subclasses.
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*
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* Must be called from the process's main thread.
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*/
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public void deliverCancellation() {
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if (mOnLoadCanceledListener != null) {
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mOnLoadCanceledListener.onLoadCanceled(this);
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}
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}
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/**
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* @return an application context retrieved from the Context passed to the constructor.
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*/
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public Context getContext() {
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return mContext;
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}
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/**
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* @return the ID of this loader
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*/
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public int getId() {
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return mId;
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}
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/**
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* Registers a class that will receive callbacks when a load is complete.
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* The callback will be called on the process's main thread so it's safe to
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* pass the results to widgets.
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*
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* <p>Must be called from the process's main thread.
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*/
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public void registerListener(int id, OnLoadCompleteListener<D> listener) {
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if (mListener != null) {
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throw new IllegalStateException("There is already a listener registered");
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}
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mListener = listener;
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mId = id;
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}
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/**
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* Remove a listener that was previously added with {@link #registerListener}.
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*
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* Must be called from the process's main thread.
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*/
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public void unregisterListener(OnLoadCompleteListener<D> listener) {
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if (mListener == null) {
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throw new IllegalStateException("No listener register");
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}
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if (mListener != listener) {
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throw new IllegalArgumentException("Attempting to unregister the wrong listener");
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}
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mListener = null;
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}
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/**
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* Registers a listener that will receive callbacks when a load is canceled.
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* The callback will be called on the process's main thread so it's safe to
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* pass the results to widgets.
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*
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* Must be called from the process's main thread.
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*
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* @param listener The listener to register.
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*/
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public void registerOnLoadCanceledListener(OnLoadCanceledListener<D> listener) {
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if (mOnLoadCanceledListener != null) {
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throw new IllegalStateException("There is already a listener registered");
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}
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mOnLoadCanceledListener = listener;
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}
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/**
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* Unregisters a listener that was previously added with
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* {@link #registerOnLoadCanceledListener}.
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*
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* Must be called from the process's main thread.
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*
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* @param listener The listener to unregister.
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*/
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public void unregisterOnLoadCanceledListener(OnLoadCanceledListener<D> listener) {
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if (mOnLoadCanceledListener == null) {
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throw new IllegalStateException("No listener register");
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}
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if (mOnLoadCanceledListener != listener) {
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throw new IllegalArgumentException("Attempting to unregister the wrong listener");
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}
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mOnLoadCanceledListener = null;
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}
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/**
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* Return whether this load has been started. That is, its {@link #startLoading()}
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* has been called and no calls to {@link #stopLoading()} or
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* {@link #reset()} have yet been made.
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*/
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public boolean isStarted() {
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return mStarted;
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}
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/**
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* Return whether this loader has been abandoned. In this state, the
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* loader <em>must not</em> report any new data, and <em>must</em> keep
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* its last reported data valid until it is finally reset.
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*/
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public boolean isAbandoned() {
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return mAbandoned;
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}
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/**
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* Return whether this load has been reset. That is, either the loader
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* has not yet been started for the first time, or its {@link #reset()}
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* has been called.
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*/
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public boolean isReset() {
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return mReset;
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}
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/**
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* This function will normally be called for you automatically by
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* {@link android.app.LoaderManager} when the associated fragment/activity
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* is being started. When using a Loader with {@link android.app.LoaderManager},
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* you <em>must not</em> call this method yourself, or you will conflict
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* with its management of the Loader.
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*
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* Starts an asynchronous load of the Loader's data. When the result
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* is ready the callbacks will be called on the process's main thread.
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* If a previous load has been completed and is still valid
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* the result may be passed to the callbacks immediately.
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* The loader will monitor the source of
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* the data set and may deliver future callbacks if the source changes.
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* Calling {@link #stopLoading} will stop the delivery of callbacks.
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*
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* <p>This updates the Loader's internal state so that
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* {@link #isStarted()} and {@link #isReset()} will return the correct
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* values, and then calls the implementation's {@link #onStartLoading()}.
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*
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* <p>Must be called from the process's main thread.
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*/
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public final void startLoading() {
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mStarted = true;
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mReset = false;
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mAbandoned = false;
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onStartLoading();
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}
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/**
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* Subclasses must implement this to take care of loading their data,
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* as per {@link #startLoading()}. This is not called by clients directly,
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* but as a result of a call to {@link #startLoading()}.
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*/
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protected void onStartLoading() {
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}
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/**
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* Attempt to cancel the current load task.
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* Must be called on the main thread of the process.
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*
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* <p>Cancellation is not an immediate operation, since the load is performed
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* in a background thread. If there is currently a load in progress, this
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* method requests that the load be canceled, and notes this is the case;
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* once the background thread has completed its work its remaining state
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* will be cleared. If another load request comes in during this time,
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* it will be held until the canceled load is complete.
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*
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* @return Returns <tt>false</tt> if the task could not be canceled,
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* typically because it has already completed normally, or
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* because {@link #startLoading()} hasn't been called; returns
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* <tt>true</tt> otherwise. When <tt>true</tt> is returned, the task
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* is still running and the {@link OnLoadCanceledListener} will be called
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* when the task completes.
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*/
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public boolean cancelLoad() {
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return onCancelLoad();
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}
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/**
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* Subclasses must implement this to take care of requests to {@link #cancelLoad()}.
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* This will always be called from the process's main thread.
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*
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* @return Returns <tt>false</tt> if the task could not be canceled,
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* typically because it has already completed normally, or
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* because {@link #startLoading()} hasn't been called; returns
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* <tt>true</tt> otherwise. When <tt>true</tt> is returned, the task
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* is still running and the {@link OnLoadCanceledListener} will be called
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* when the task completes.
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*/
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protected boolean onCancelLoad() {
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return false;
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}
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/**
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* Force an asynchronous load. Unlike {@link #startLoading()} this will ignore a previously
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* loaded data set and load a new one. This simply calls through to the
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* implementation's {@link #onForceLoad()}. You generally should only call this
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* when the loader is started -- that is, {@link #isStarted()} returns true.
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*
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* <p>Must be called from the process's main thread.
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*/
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public void forceLoad() {
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onForceLoad();
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}
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/**
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* Subclasses must implement this to take care of requests to {@link #forceLoad()}.
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* This will always be called from the process's main thread.
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*/
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protected void onForceLoad() {
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}
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/**
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* This function will normally be called for you automatically by
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* {@link android.app.LoaderManager} when the associated fragment/activity
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* is being stopped. When using a Loader with {@link android.app.LoaderManager},
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* you <em>must not</em> call this method yourself, or you will conflict
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* with its management of the Loader.
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*
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* <p>Stops delivery of updates until the next time {@link #startLoading()} is called.
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* Implementations should <em>not</em> invalidate their data at this point --
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* clients are still free to use the last data the loader reported. They will,
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* however, typically stop reporting new data if the data changes; they can
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* still monitor for changes, but must not report them to the client until and
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* if {@link #startLoading()} is later called.
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*
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* <p>This updates the Loader's internal state so that
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* {@link #isStarted()} will return the correct
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* value, and then calls the implementation's {@link #onStopLoading()}.
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*
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* <p>Must be called from the process's main thread.
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*/
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public void stopLoading() {
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mStarted = false;
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onStopLoading();
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}
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/**
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* Subclasses must implement this to take care of stopping their loader,
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* as per {@link #stopLoading()}. This is not called by clients directly,
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* but as a result of a call to {@link #stopLoading()}.
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* This will always be called from the process's main thread.
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*/
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protected void onStopLoading() {
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}
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/**
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* This function will normally be called for you automatically by
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* {@link android.app.LoaderManager} when restarting a Loader. When using
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* a Loader with {@link android.app.LoaderManager},
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* you <em>must not</em> call this method yourself, or you will conflict
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* with its management of the Loader.
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*
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* Tell the Loader that it is being abandoned. This is called prior
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* to {@link #reset} to have it retain its current data but not report
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* any new data.
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*/
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public void abandon() {
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mAbandoned = true;
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onAbandon();
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}
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/**
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* Subclasses implement this to take care of being abandoned. This is
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* an optional intermediate state prior to {@link #onReset()} -- it means that
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* the client is no longer interested in any new data from the loader,
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* so the loader must not report any further updates. However, the
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* loader <em>must</em> keep its last reported data valid until the final
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* {@link #onReset()} happens. You can retrieve the current abandoned
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* state with {@link #isAbandoned}.
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*/
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protected void onAbandon() {
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}
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/**
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* This function will normally be called for you automatically by
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* {@link android.app.LoaderManager} when destroying a Loader. When using
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* a Loader with {@link android.app.LoaderManager},
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* you <em>must not</em> call this method yourself, or you will conflict
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* with its management of the Loader.
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*
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* Resets the state of the Loader. The Loader should at this point free
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* all of its resources, since it may never be called again; however, its
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* {@link #startLoading()} may later be called at which point it must be
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* able to start running again.
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*
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* <p>This updates the Loader's internal state so that
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* {@link #isStarted()} and {@link #isReset()} will return the correct
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* values, and then calls the implementation's {@link #onReset()}.
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*
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* <p>Must be called from the process's main thread.
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*/
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public void reset() {
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onReset();
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mReset = true;
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mStarted = false;
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mAbandoned = false;
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mContentChanged = false;
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mProcessingChange = false;
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}
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/**
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* Subclasses must implement this to take care of resetting their loader,
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* as per {@link #reset()}. This is not called by clients directly,
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* but as a result of a call to {@link #reset()}.
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* This will always be called from the process's main thread.
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*/
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protected void onReset() {
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}
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/**
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* Take the current flag indicating whether the loader's content had
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* changed while it was stopped. If it had, true is returned and the
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* flag is cleared.
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*/
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public boolean takeContentChanged() {
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boolean res = mContentChanged;
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mContentChanged = false;
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mProcessingChange |= res;
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return res;
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}
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/**
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* Commit that you have actually fully processed a content change that
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* was returned by {@link #takeContentChanged}. This is for use with
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* {@link #rollbackContentChanged()} to handle situations where a load
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* is cancelled. Call this when you have completely processed a load
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* without it being cancelled.
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*/
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public void commitContentChanged() {
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mProcessingChange = false;
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}
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/**
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* Report that you have abandoned the processing of a content change that
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* was returned by {@link #takeContentChanged()} and would like to rollback
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* to the state where there is again a pending content change. This is
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* to handle the case where a data load due to a content change has been
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* canceled before its data was delivered back to the loader.
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*/
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public void rollbackContentChanged() {
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if (mProcessingChange) {
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onContentChanged();
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}
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}
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/**
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* Called when {@link ForceLoadContentObserver} detects a change. The
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* default implementation checks to see if the loader is currently started;
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* if so, it simply calls {@link #forceLoad()}; otherwise, it sets a flag
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* so that {@link #takeContentChanged()} returns true.
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*
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* <p>Must be called from the process's main thread.
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*/
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public void onContentChanged() {
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if (mStarted) {
|
|
forceLoad();
|
|
} else {
|
|
// This loader has been stopped, so we don't want to load
|
|
// new data right now... but keep track of it changing to
|
|
// refresh later if we start again.
|
|
mContentChanged = true;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* For debugging, converts an instance of the Loader's data class to
|
|
* a string that can be printed. Must handle a null data.
|
|
*/
|
|
public String dataToString(D data) {
|
|
StringBuilder sb = new StringBuilder(64);
|
|
DebugUtils.buildShortClassTag(data, sb);
|
|
sb.append("}");
|
|
return sb.toString();
|
|
}
|
|
|
|
@Override
|
|
public String toString() {
|
|
StringBuilder sb = new StringBuilder(64);
|
|
DebugUtils.buildShortClassTag(this, sb);
|
|
sb.append(" id=");
|
|
sb.append(mId);
|
|
sb.append("}");
|
|
return sb.toString();
|
|
}
|
|
|
|
/**
|
|
* Print the Loader's state into the given stream.
|
|
*
|
|
* @param prefix Text to print at the front of each line.
|
|
* @param fd The raw file descriptor that the dump is being sent to.
|
|
* @param writer A PrintWriter to which the dump is to be set.
|
|
* @param args Additional arguments to the dump request.
|
|
*/
|
|
public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
|
|
writer.print(prefix); writer.print("mId="); writer.print(mId);
|
|
writer.print(" mListener="); writer.println(mListener);
|
|
if (mStarted || mContentChanged || mProcessingChange) {
|
|
writer.print(prefix); writer.print("mStarted="); writer.print(mStarted);
|
|
writer.print(" mContentChanged="); writer.print(mContentChanged);
|
|
writer.print(" mProcessingChange="); writer.println(mProcessingChange);
|
|
}
|
|
if (mAbandoned || mReset) {
|
|
writer.print(prefix); writer.print("mAbandoned="); writer.print(mAbandoned);
|
|
writer.print(" mReset="); writer.println(mReset);
|
|
}
|
|
}
|
|
}
|