core/java/android/database/BulkCursorToCursorAdaptor.java

/*
 * Copyright (C) 2006 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.Bundle;
import android.os.RemoteException;
import android.util.Log;

/**
 * Adapts an {@link IBulkCursor} to a {@link Cursor} for use in the local process.
 *
 * {@hide}
 */
public final class BulkCursorToCursorAdaptor extends AbstractWindowedCursor {
    private static final String TAG = "BulkCursor";

    private SelfContentObserver mObserverBridge = new SelfContentObserver(this);
    private IBulkCursor mBulkCursor;
    private int mCount;
    private String[] mColumns;
    private boolean mWantsAllOnMoveCalls;

    /**
     * Initializes the adaptor.
     * Must be called before first use.
     */
    public void initialize(IBulkCursor bulkCursor, int count, int idIndex) {
        mBulkCursor = bulkCursor;
        mColumns = null;  // lazily retrieved
        mCount = count;
        mRowIdColumnIndex = idIndex;
    }

    /**
     * Returns column index of "_id" column, or -1 if not found.
     */
    public static int findRowIdColumnIndex(String[] columnNames) {
        int length = columnNames.length;
        for (int i = 0; i < length; i++) {
            if (columnNames[i].equals("_id")) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Gets a SelfDataChangeOberserver that can be sent to a remote
     * process to receive change notifications over IPC.
     *
     * @return A SelfContentObserver hooked up to this Cursor
     */
    public IContentObserver getObserver() {
        return mObserverBridge.getContentObserver();
    }

    private void throwIfCursorIsClosed() {
        if (mBulkCursor == null) {
            throw new StaleDataException("Attempted to access a cursor after it has been closed.");
        }
    }

    @Override
    public int getCount() {
        throwIfCursorIsClosed();
        return mCount;
    }

    @Override
    public boolean onMove(int oldPosition, int newPosition) {
        throwIfCursorIsClosed();

        try {
            // Make sure we have the proper window
            if (mWindow != null) {
                if (newPosition < mWindow.getStartPosition() ||
                        newPosition >= (mWindow.getStartPosition() + mWindow.getNumRows())) {
                    setWindow(mBulkCursor.getWindow(newPosition));
                } else if (mWantsAllOnMoveCalls) {
                    mBulkCursor.onMove(newPosition);
                }
            } else {
                setWindow(mBulkCursor.getWindow(newPosition));
            }
        } catch (RemoteException ex) {
            // We tried to get a window and failed
            Log.e(TAG, "Unable to get window because the remote process is dead");
            return false;
        }

        // Couldn't obtain a window, something is wrong
        if (mWindow == null) {
            return false;
        }

        return true;
    }

    @Override
    public void deactivate() {
        // This will call onInvalidated(), so make sure to do it before calling release,
        // which is what actually makes the data set invalid.
        super.deactivate();

        if (mBulkCursor != null) {
            try {
                mBulkCursor.deactivate();
            } catch (RemoteException ex) {
                Log.w(TAG, "Remote process exception when deactivating");
            }
        }
    }
    
    @Override
    public void close() {
        super.close();

        if (mBulkCursor != null) {
            try {
                mBulkCursor.close();
            } catch (RemoteException ex) {
                Log.w(TAG, "Remote process exception when closing");
            } finally {
                mBulkCursor = null;
            }
        }
    }

    @Override
    public boolean requery() {
        throwIfCursorIsClosed();

        try {
            CursorWindow newWindow = new CursorWindow(false /* create a remote window */);
            try {
                mCount = mBulkCursor.requery(getObserver(), newWindow);
                if (mCount != -1) {
                    mPos = -1;
                    closeWindow();

                    // super.requery() will call onChanged. Do it here instead of relying on the
                    // observer from the far side so that observers can see a correct value for mCount
                    // when responding to onChanged.
                    super.requery();
                    return true;
                } else {
                    deactivate();
                    return false;
                }
            } finally {
                // Don't take ownership of the window until the next call to onMove.
                newWindow.close();
            }
        } catch (Exception ex) {
            Log.e(TAG, "Unable to requery because the remote process exception " + ex.getMessage());
            deactivate();
            return false;
        }
    }

    @Override
    public String[] getColumnNames() {
        throwIfCursorIsClosed();

        if (mColumns == null) {
            try {
                mColumns = mBulkCursor.getColumnNames();
            } catch (RemoteException ex) {
                Log.e(TAG, "Unable to fetch column names because the remote process is dead");
                return null;
            }
        }
        return mColumns;
    }

    @Override
    public Bundle getExtras() {
        throwIfCursorIsClosed();

        try {
            return mBulkCursor.getExtras();
        } catch (RemoteException e) {
            // This should never happen because the system kills processes that are using remote
            // cursors when the provider process is killed.
            throw new RuntimeException(e);
        }
    }

    @Override
    public Bundle respond(Bundle extras) {
        throwIfCursorIsClosed();

        try {
            return mBulkCursor.respond(extras);
        } catch (RemoteException e) {
            // the system kills processes that are using remote cursors when the provider process
            // is killed, but this can still happen if this is being called from the system process,
            // so, better to log and return an empty bundle.
            Log.w(TAG, "respond() threw RemoteException, returning an empty bundle.", e);
            return Bundle.EMPTY;
        }
    }
}