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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.Cursor;
import android.net.Uri;
import android.os.CancellationSignal;
import android.os.OperationCanceledException;
import java.io.FileDescriptor;
import java.io.PrintWriter;
import java.util.Arrays;
/**
* A loader that queries the {@link ContentResolver} and returns a {@link Cursor}.
* This class implements the {@link Loader} protocol in a standard way for
* querying cursors, building on {@link AsyncTaskLoader} to perform the cursor
* query on a background thread so that it does not block the application's UI.
*
* A CursorLoader must be built with the full information for the query to
* perform, either through the
* {@link #CursorLoader(Context, Uri, String[], String, String[], String)} or
* creating an empty instance with {@link #CursorLoader(Context)} and filling
* in the desired paramters with {@link #setUri(Uri)}, {@link #setSelection(String)},
* {@link #setSelectionArgs(String[])}, {@link #setSortOrder(String)},
* and {@link #setProjection(String[])}.
*/
public class CursorLoader extends AsyncTaskLoader {
final ForceLoadContentObserver mObserver;
Uri mUri;
String[] mProjection;
String mSelection;
String[] mSelectionArgs;
String mSortOrder;
Cursor mCursor;
CancellationSignal mCancellationSignal;
/* Runs on a worker thread */
@Override
public Cursor loadInBackground() {
synchronized (this) {
if (isLoadInBackgroundCanceled()) {
throw new OperationCanceledException();
}
mCancellationSignal = new CancellationSignal();
}
try {
Cursor cursor = getContext().getContentResolver().query(mUri, mProjection, mSelection,
mSelectionArgs, mSortOrder, mCancellationSignal);
if (cursor != null) {
try {
// Ensure the cursor window is filled.
cursor.getCount();
cursor.registerContentObserver(mObserver);
} catch (RuntimeException ex) {
cursor.close();
throw ex;
}
}
return cursor;
} finally {
synchronized (this) {
mCancellationSignal = null;
}
}
}
@Override
public void cancelLoadInBackground() {
super.cancelLoadInBackground();
synchronized (this) {
if (mCancellationSignal != null) {
mCancellationSignal.cancel();
}
}
}
/* Runs on the UI thread */
@Override
public void deliverResult(Cursor cursor) {
if (isReset()) {
// An async query came in while the loader is stopped
if (cursor != null) {
cursor.close();
}
return;
}
Cursor oldCursor = mCursor;
mCursor = cursor;
if (isStarted()) {
super.deliverResult(cursor);
}
if (oldCursor != null && oldCursor != cursor && !oldCursor.isClosed()) {
oldCursor.close();
}
}
/**
* Creates an empty unspecified CursorLoader. You must follow this with
* calls to {@link #setUri(Uri)}, {@link #setSelection(String)}, etc
* to specify the query to perform.
*/
public CursorLoader(Context context) {
super(context);
mObserver = new ForceLoadContentObserver();
}
/**
* Creates a fully-specified CursorLoader. See
* {@link ContentResolver#query(Uri, String[], String, String[], String)
* ContentResolver.query()} for documentation on the meaning of the
* parameters. These will be passed as-is to that call.
*/
public CursorLoader(Context context, Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
super(context);
mObserver = new ForceLoadContentObserver();
mUri = uri;
mProjection = projection;
mSelection = selection;
mSelectionArgs = selectionArgs;
mSortOrder = sortOrder;
}
/**
* 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.
*
* Must be called from the UI thread
*/
@Override
protected void onStartLoading() {
if (mCursor != null) {
deliverResult(mCursor);
}
if (takeContentChanged() || mCursor == null) {
forceLoad();
}
}
/**
* Must be called from the UI thread
*/
@Override
protected void onStopLoading() {
// Attempt to cancel the current load task if possible.
cancelLoad();
}
@Override
public void onCanceled(Cursor cursor) {
if (cursor != null && !cursor.isClosed()) {
cursor.close();
}
}
@Override
protected void onReset() {
super.onReset();
// Ensure the loader is stopped
onStopLoading();
if (mCursor != null && !mCursor.isClosed()) {
mCursor.close();
}
mCursor = null;
}
public Uri getUri() {
return mUri;
}
public void setUri(Uri uri) {
mUri = uri;
}
public String[] getProjection() {
return mProjection;
}
public void setProjection(String[] projection) {
mProjection = projection;
}
public String getSelection() {
return mSelection;
}
public void setSelection(String selection) {
mSelection = selection;
}
public String[] getSelectionArgs() {
return mSelectionArgs;
}
public void setSelectionArgs(String[] selectionArgs) {
mSelectionArgs = selectionArgs;
}
public String getSortOrder() {
return mSortOrder;
}
public void setSortOrder(String sortOrder) {
mSortOrder = sortOrder;
}
@Override
public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) {
super.dump(prefix, fd, writer, args);
writer.print(prefix); writer.print("mUri="); writer.println(mUri);
writer.print(prefix); writer.print("mProjection=");
writer.println(Arrays.toString(mProjection));
writer.print(prefix); writer.print("mSelection="); writer.println(mSelection);
writer.print(prefix); writer.print("mSelectionArgs=");
writer.println(Arrays.toString(mSelectionArgs));
writer.print(prefix); writer.print("mSortOrder="); writer.println(mSortOrder);
writer.print(prefix); writer.print("mCursor="); writer.println(mCursor);
writer.print(prefix); writer.print("mContentChanged="); writer.println(mContentChanged);
}
}