Android 3.0 introduced the Loader framework, and the
Android Compatibility Library allows you to use that
framework going back to Android 1.6. However, the only
supplied concrete implementation of a Loader is
CursorLoader, and that is only for use with a
ContentProvider. Moreover, while the Loader framework
handles database queries in the background, it does not
help with the rest of your CRUD operations.
This LoaderEx project is designed to help fill some
of those gaps. Presently, it provides a SQLiteCursorLoader,
offering the same basic concept as CursorLoader, but
for use with a SQLiteDatabase instead of a ContentProvider.
It also supplies some boilerplate AsyncTasks to handle
database inserts and deletes in the background. It also supplies:
SQLCipherCursorLoader, for operations with SQLCipher for AndroidSharedPreferencesLoader, for retrieving the defaultSharedPreferencesobject without tying up the main application thread.
This is packaged as an Android library project, though a simple
JAR is also available. If you are working on a native Honeycomb
application (i.e., not using the Android Compatibility
Library), please use the JAR — putting it in your project's
libs/ directory should be sufficient.
Generally speaking, you use SQLiteCursorLoader in the same
fashion as you would use CursorLoader — by having your
activity implement LoaderManager.LoaderCallbacks<Cursor>
and calling initLoader() on the LoaderManager. Then, in
your onCreateLoader() callback method, you can return a
properly-constructed SQLiteCursorLoader. Everything else
behaves as CursorLoader does.
There is only one at this time, taking a SQLiteDatabase
object, plus the same parameters as is used by rawQuery()
on SQLiteOpenHelper — a String with your SQL query
and a String[] of positional parameter values (to replace
any ? you have in your query).
NOTE: Version 0.4 and previous of this component took a
SQLiteDatabase as a parameter instead of a SQLiteOpenHelper.
The change was made so that database creation and upgrades can
occur on the background thread. Apologies for the API change.
There are two implementations of SQLiteCursorLoader, in
two separate packages.
The one in com.commonsware.cwac.loaderex works using
the native API Level 11+ implementation of the Loader
framework.
The one in com.commonsware.cwac.loaderex.acl works
using the implementation of the Loader framework from
the Android Compatibility Library (ACL). You will need to
have the ACL as part of your build path in addition to having
the JAR or library project of LoaderEx.
In your code, you will choose the one you wish to use based upon whether you are using the ACL or not.
If you use the insert(), update(), delete(), replace(), and
execSQL() methods on SQLiteCursorLoader, the loader
framework will automatically update you to reflect a new
Cursor with the changed data. These methods take
the same parameters as they do on SQLiteDatabase.
SQLiteCursorLoader itself extends an AbstractCursorLoader.
AbstractCursorLoader is much of the logic from the ACL's
CursorLoader, but with the actual query code abstracted
out. You are welcome to make your own subclasses of
AbstractCursorLoader if you are creating Cursors from
other sources. Just override buildCursor() and have it
return the Cursor — this method is called on a
background thread and therefore is not time-limited.
THESE CLASSES ARE DEPRECATED
SQLiteInsertTask and SQLiteDeleteTask are also supplied
in this library. These simply perform insert() and delete()
calls on a SQLiteDatabase inside an AsyncTask, to get that
work off the main application thread. These classes are designed
to work on API Level 5 or higher and as such are not
Loader-aware.
However, you can arrange to do post-CRUD work by extending
these classes and overriding onPostExecute(Exception):
new SQLiteInsertTask(db.getWritableDatabase(),
"constants", DatabaseHelper.TITLE,
values) {
@Override
public void onPostExecute(Exception e) {
getLoaderManager().restartLoader(0, null,
ConstantsBrowser.this);
}
}.execute();
The Exception will be null if everything succeeded in
the background work; otherwise, it will be whatever Exception
was raised by the insert() call, etc.
SQLiteDatabase itself is thread-safe, in that it manages
a lock to ensure that two operations do not occur in
parallel. However, that assumes you are using a single
instance of SQLiteDatabase. Hence, if you are using
SQLiteCursorLoader and the other classes in this project
you will want to make sure that you are using a single
instance of your SQLiteDatabase object. If you have more than
one component using the database, that SQLiteDatabase
effectively will have to be global in scope, such as by
holding onto it (or its containing SQLiteOpenHelper)
in a static data member.
This class works nearly identically to SQLiteCursorLoader.
The biggest difference is that it takes a SQLCipher for Android
version of SQLiteDatabase in its constructor, instead of
a SQLiteOpenHelper. The SQLiteDatabase will need to be readable or
writeable depending on what you are doing with it.
As with SQLiteCursorLoader, there are two editions of SQLCipherCursorLoader,
one in com.commonsware.cwac.loaderex and one in
com.commonsware.cwac.loaderex.acl — the latter is for use with the
Android Support package's version of the Loader framework.
Apps using SQLCipherCursorLoader will need a full copy
of SQLCipher for Android in their project for the project to
run properly.
There is a SQLCipherUtils class in com.commonsware.cwac.loaderex with
a couple of static methods that may be useful to those implementing SQLCipher
for Android in their projects.
getDatabaseState() will return a SQLCipherUtils.State enum indicating
what the state of the database is:
DOES_NOT_EXIST, meaning that we cannot find a database fileUNENCRYPTED, meaning that we have found a database file and believe that it is unencryptedENCRYPTED, meaning that we have found a database file and believe that it is encrypted, andUNKNOWN, meaning that we do not know what is going on with the database
getDatabaseState() takes a Context and the name of the database as parameters.
encrypt() will replace an unencrypted database
with an encrypted version, given the supplied Context, the name of the database,
and the passphrase to use for encryption.
SharedPreferencesLoader largely mirrors SQLiteCursorLoader:
-
There are two implementations, one for native API Level 11+ development (in the base
com.commonsware.cwac.loaderexpackage) and one for use with the Android Support package (in thecom.commonsware.cwac.loaderex.aclpackage). -
Your activity should implement the
LoaderManager.LoaderCallbacks<SharedPreferences>interface. -
In your
onCreateLoader()method, return an instance ofSharedPreferencesLoader, which has a one-parameter constructor taking yourActivity(or otherContext) as the parameter. -
In your
onLoadFinished()method, make use of theSharedPreferencesobject delivered unto you.
In addition, there is a static persist() method that takes
a SharedPreferences.Editor object and arranges to save those
edits on a background thread, regardless of Android API level.
This project sometimes depends on the Android Support package
(formerly the Android Compatibility Library, or ACL). If you
are using it in source form as an Android
library project, you will need the Android Support package.
If you are using the JAR, you only need the Android Support
package if you are using the .acl editions of the classes.
This project should work on API Level 7 and higher, except for any portions that may be noted otherwise in this document. Please report bugs if you find features that do not work on API Level 7 and are not noted as requiring a higher version.
This is version v0.7.1 of this module, meaning that its author really should consider formalizing v1.0.0 before too long...
In the demo/ sub-project you will find
a sample activity that demonstrates the use of SQLiteCursorLoader.
There are two implementations of this sample, one for the
Android Support package and one for native API Level 11 work.
There are also sample activities demonstrating the use
of SharedPreferencesLoader.
Note that when you build the JAR via ant jar, the sample
activity is not included, nor any resources -- only the
compiled classes for the actual library are put into the JAR.
Future editions of this project will add things like
support for query() in addition to rawQuery()-style queries
The code in this project is licensed under the Apache Software License 2.0, per the terms of the included LICENSE file.
If you have questions regarding the use of this code, please post a question
on StackOverflow tagged with commonsware and android. Be sure to indicate
what CWAC module you are having issues with, and be sure to include source code
and stack traces if you are encountering crashes.
If you have encountered what is clearly a bug, please post an issue. Be certain to include complete steps for reproducing the issue.
Do not ask for help via Twitter.
- v0.7.1: bug fix
- v0.7.0: added SQLCipher for Android support
- v0.6.0: added
replace()(by request) - v0.5.0: switched to taking a
SQLiteOpenHelperinstead of aSQLiteDatabase - v0.4.0: added
insert(),update(),delete(), andexecSQL(); better on-change support - v0.3.0: added
SharedPreferencesLoader - v0.2.0: added
SQLiteInsertTaskandSQLiteDeleteTask - v0.1.0: initial release
