Android Open Source - watchme Generic Cursor Loader

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License

The source code is released under:

Copyright (c) 2012 Johan Brook, Robin Andersson, Lisa Stenberg, Mattias Henriksson Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documen...

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Java Source Code

/**
 *  GenericCursorLoader.java//from  w w w .  j  a va 2  s.  c  o m
 *
 *  Static library support version of the framework's
 *  {@link android.content.CursorLoader}. Used to write apps that run on
 *  platforms prior to Android 3.0. When running on Android 3.0 or above, this
 *  implementation is still used; it does not try to switch to the framework's
 *  implementation. See the framework SDK documentation for a class overview.
 * 
 *  A CursorLoader that has a ICursorHelper that calculates the cursor.
 *
 *  @author lisastenberg
 *  @copyright (c) 2012 Johan Brook, Robin Andersson, Lisa Stenberg, Mattias Henriksson
 *  @license MIT
 */

package se.chalmers.watchme.database;

import android.content.Context;
import android.database.ContentObserver;
import android.database.Cursor;
import android.net.Uri;
import android.os.CancellationSignal;
import android.support.v4.content.CursorLoader;

import java.io.FileDescriptor;
import java.io.PrintWriter;

public class GenericCursorLoader extends CursorLoader {

  private final ForceLoadContentObserver mObserver;
  private Uri mUri;

  private String mSortOrder;

  private Cursor mCursor;
  private CancellationSignal mCancellationSignal;

  private ICursorHelper mCursorHelper;

  /**
   * 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 GenericCursorLoader(Context context) {
    super(context);
    mObserver = new ForceLoadContentObserver();
  }

  /**
   * Creates a CursorLoader with a cursorHelper that is used to calculate the
   * Cursor in loadCursor()
   * 
   * @param context
   *            The context
   * @param cursorHelper
   *            The CursorHelper
   */
  public GenericCursorLoader(Context context, ICursorHelper cursorHelper) {
    super(context);
    mObserver = new ForceLoadContentObserver();
    mCursorHelper = cursorHelper;

    mUri = mCursorHelper.getUri();
    mSortOrder = mCursorHelper.getSortOrder();
  }

  /* Runs on a worker thread */
  @Override
  public Cursor loadInBackground() {
    synchronized (this) {
      mCancellationSignal = new CancellationSignal();
    }
    try {

      Cursor cursor = mCursorHelper.getCursor();
      if (cursor != null) {

        // Ensure the cursor window is filled
        cursor.getCount();
        registerContentObserver(cursor, mObserver);
      }
      return cursor;
    } finally {
      synchronized (this) {
        mCancellationSignal = null;
      }
    }
  }

  /**
   * Registers an observer to get notifications from the content provider when
   * the cursor needs to be refreshed.
   */
  void registerContentObserver(Cursor cursor, ContentObserver observer) {
    cursor.registerContentObserver(mObserver);
  }

  /* 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();
    }
  }

  /**
   * 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;
  }

  @Override
  public Uri getUri() {
    return mUri;
  }

  @Override
  public void setUri(Uri uri) {
    this.mUri = uri;
  }

  @Override
  public String getSortOrder() {
    return mSortOrder;
  }

  @Override
  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("mSortOrder=");
    writer.println(mSortOrder);
    writer.print(prefix);
    writer.print("mCursor=");
    writer.println(mCursor);
    writer.print(prefix);
  }

}

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