com.commonsware.cwac.loaderex.AbstractCursorLoader.java Source code

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Here is the source code for com.commonsware.cwac.loaderex.AbstractCursorLoader.java

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/*
 * Copyright (c) 2011-2012 CommonsWare, LLC
 * portions Copyright (C) 2011 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 com.commonsware.cwac.loaderex;

import android.content.Context;
import android.database.Cursor;
import android.support.v4.content.AsyncTaskLoader;

abstract public class AbstractCursorLoader extends AsyncTaskLoader<Cursor> {
    abstract protected Cursor buildCursor();

    Cursor lastCursor = null;

    public AbstractCursorLoader(Context context) {
        super(context);
    }

    /** 
     * Runs on a worker thread, loading in our data. Delegates
     * the real work to concrete subclass' buildCursor() method. 
     */
    @Override
    public Cursor loadInBackground() {
        Cursor cursor = buildCursor();

        if (cursor != null) {
            // Ensure the cursor window is filled
            cursor.getCount();
        }

        return (cursor);
    }

    /**
     * Runs on the UI thread, routing the results from the
     * background thread to whatever is using the Cursor
     * (e.g., a CursorAdapter).
     */
    @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 = lastCursor;
        lastCursor = cursor;

        if (isStarted()) {
            super.deliverResult(cursor);
        }

        if (oldCursor != null && oldCursor != cursor && !oldCursor.isClosed()) {
            oldCursor.close();
        }
    }

    /**
     * Starts an asynchronous load of the 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 (lastCursor != null) {
            deliverResult(lastCursor);
        }

        if (takeContentChanged() || lastCursor == null) {
            forceLoad();
        }
    }

    /**
     * Must be called from the UI thread, triggered by a
     * call to stopLoading().
     */
    @Override
    protected void onStopLoading() {
        // Attempt to cancel the current load task if possible.
        cancelLoad();
    }

    /**
     * Must be called from the UI thread, triggered by a
     * call to cancel(). Here, we make sure our Cursor
     * is closed, if it still exists and is not already closed.
     */
    @Override
    public void onCanceled(Cursor cursor) {
        if (cursor != null && !cursor.isClosed()) {
            cursor.close();
        }
    }

    /**
     * Must be called from the UI thread, triggered by a
     * call to reset(). Here, we make sure our Cursor
     * is closed, if it still exists and is not already closed.
     */
    @Override
    protected void onReset() {
        super.onReset();

        // Ensure the loader is stopped
        onStopLoading();

        if (lastCursor != null && !lastCursor.isClosed()) {
            lastCursor.close();
        }

        lastCursor = null;
    }
}