Android Open Source - Loaders Abstract Cursor Loader

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License

The source code is released under:

Apache License

Java Source Code

package com.github.vsouhrada.loaders;
/* w w w .j  a va 2 s . c o m*/
import android.content.Context;
import android.database.Cursor;
import android.support.v4.content.AsyncTaskLoader;


/**
 * This class can be useful in case of that you need to work with Cursor object without usage of the ContentResolver.
 * @author vsouhrada
 * @see android.support.v4.content.AsyncTaskLoader< android.database.Cursor>
 * @version 1.0.0
 * @since 1.0.0
 * 
 */
public abstract class AbstractCursorLoader extends AsyncTaskLoader<Cursor> {

  private Cursor lastCursor;

  /**
   * Create and return {@linkplain android.database.Cursor} which is currently using.
   * 
   * @return Cursor which is currently using.
   * @since 1.0.0
   */
  abstract protected Cursor buildCursor();

  /**
   * Default constructor
   *
   * @param context current application environment
   * @since 1.0.0
   */
  public AbstractCursorLoader(Context context) {
    super(context);
  }

  /**
   * Run it on worker thread to perform the data load.
   * 
   * @since 1.0.0
   */
  @Override
  public Cursor loadInBackground() {
    Cursor cursor = buildCursor();

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

    return cursor;
  }

  /**
   * Runs on the UI thread. Delivering the results from the background thread to
   * whatever is using the Cursor.
   * 
   * @param cursor
   *          current Cursor
   * @since 1.0.0
   */
  @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()) {
      // If the Loader is currently started, we can immediately
      // deliver its results.
      super.deliverResult(cursor);
    }

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

  /**
   * Starts an asynchronous load of 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
   * 
   * @since 1.0.0
   */
  @Override
  protected void onStartLoading() {
    if (lastCursor != null) {
      // If we currently have a result available, deliver it
      // immediately.
      deliverResult(lastCursor);
    }

    if (takeContentChanged() || lastCursor == null) {
      // If the cursor has changed since the last time it was loaded
      // or is not currently available, start a load.
      forceLoad();
    }
  }

  /**
   * Must be called from the UI thread, triggered by a call to stopLoading().
   * 
   * @since 1.0.0
   */
  @Override
  protected void onStopLoading() {
    // Attempt to cancel the current load task if possible.
    cancelLoad();
  }

  /**
   * {@inheritDoc}
   *
   * @param cursor instance of current {@link android.database.Cursor} object which is wrapped by this class.
   * @since 1.0.0
   */
  @Override
  public void onCanceled(Cursor cursor) {
    // Attempt to cancel the current asynchronous load.
    super.onCanceled(cursor);

    // The load has been canceled, so we should release the resources
    // associated with cursor.
    onReleaseResources(cursor);
  }

  /**
   * Handles a request to resetting loader.
   * This will always be called from the process's main thread.
   *
   * @since 1.0.0
   */
  @Override
  protected void onReset() {
    super.onReset();

    // Ensure the loader has been stopped.
    onStopLoading();

    // At this point we can release the resources associated with lastCursor.
    onReleaseResources(lastCursor);

    lastCursor = null;
  }

  /**
   * Release the resources associated with {@link android.database.Cursor}
   * 
   * @param cursor
   *          instance of Cursor
   * @since 1.0.0
   */
  protected void onReleaseResources(Cursor cursor) {
    if (cursor != null && !cursor.isClosed()) {
      cursor.close();
    }
  }

}

Java Source Code List

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