android - CursorLoader & SQLite without Content Provider

Question

I know this has been discussed yet I wanted to ask about the current state of the matter. Do i have to create a ContentProvider to use CursorLoader in connection with a sqlite database?

I found

CursorLoader usage without ContentProvider

Looks exactly what I was hoping for yet as Emmby commented

• Users should be aware of one limitation, which is that it has no mechanism to refresh on data changes (as Loaders are supposed to do)

So another solution is mentioned

https://github.com/commonsguy/cwac-loaderex

yet again some drawback is pointed out

• However, to make use of the automatic re-querying, you need to use the same loader for the UI as well as for the updates, limiting its usability for background services.

Of course when using LoaderManager we want to get all the benefits for which it was introduced. So my question is if there is a way to use LoaderManager in connection with a sqlite database without having to implement a content provider yet have all the benefits of it.

Thanks

Veteran

Answer 1

The two implementations you mention in your post both offer all of the benefits of the CursorLoader except the ability to receive notifications when the underlying content changes.

I've been looking into this a lot recently and I can confidently tell you that the Android API currently does not provide a means of doing this with only a raw SQLiteDatabase (it only provides the ContentResolver#notifyChange() and Cursor#setNotificationUri() methods, which are used to notify all Cursors registered under a certain notification Uri).

That said, your options right now are to:

1. Implement an observer yourself that is capable of receiving notifications from the SQLiteDatabase when the content changes, and is somehow able to relay these notifications to all existing Loaders in your application. I wrote a pretty extensive blog post on how to implement Loaders that might come in handy if you wish to take on this challenge. Or...

2. Use Mark Murphy's LoaderEx library and only make database modifications using the AsyncTask operations his library provides. Note that the reason why his tasks refresh the Loader is because they call onContentChanged on the Loader immediately after the insertion/update/delete is performed, effectively telling the Loader that the content has changed and that it should refresh its data.

3. Just use a ContentProvider with a CursorLoader and you can use the ContentResolver#notifyChange() method to notify the CursorLoader that a content change has occurred.

I'm trying to figure out a better solution, and I'll report back in the future if I ever find/implement one, but for now these will have to do.

Loireatlantique

Great, thanks for this detailed response. Taking this I just feel I should implement a content provider even so it seems like a overkill for any small database i might want to list on the display. Hmmm ... – Veteran

@Veteran Yeah, that's what I usually do too. I really want to find a way to find a way to do it though... I'm not finished with this yet :) – Loireatlantique

love androiddesignpatterns.com by the way - very helpful and what I want to look into after having done my first steps in the android world – Veteran

@Veteran Thanks! Until then, I'll try to write some more cool stuff :P – Loireatlantique

Any news here? Can one do it without using ContentProvider? – Archiphoneme

On the other hand, what exactly the drawback with ContentProvider? As I know, the contentProvider is nothing more a mapping layer. And if I set my provider with android:exported="false". It would not visible for other apps. – Temptress

@Temptress There is no drawback other than it requires a little bit more code. It's literally just an abstraction layer over a private data store. – Loireatlantique

@AlexLockwood, does it mean in order to load data in async manner and get notifications of data changes we need (and it is recommended way?) to implement a ContentProvider in first place? I thought the purpose of ContentProviders is to share data with other application, as it stands in their description, but looks like it is not the only purpose. – Yam

@Yam The global notifications that come with a content provider is not "the purpose" of a content provider... it is just an additional feature. The main purpose of the content provider is to allow for the sharing of data with other applications. – Loireatlantique

@Temptress ~"what exactly the drawback with ContentProvider?" If you have multiple ContentProviders in your application, then you will have to synchronize them yourself, as they are not thread-safe. – Borras

@AlexLockwood Please, do you think you could help with this #27257916? – Intramundane

@AlexLockwood To use CursorLoader we will use ContentProvider instead of Common database. But documentation claims that ContentProviders are used to share data among two apps. And Other side it is said that "Google re-commanded CursorLoader to get data from a database." Why so ? And is There any way through which i can set data of a Cursor to a recyclerView (in onBindView() method) directly ? – Synovia

Answer 2

Here is my solution, in my onCreateLoader

{
Uri u = Uri.parse("content://what_string_you_want");
return new CursorLoader(this, yourURI, projection, null, null, null) {
    private final ForceLoadContentObserver mObserver = new ForceLoadContentObserver();

    @Override
    public Cursor loadInBackground() {
        Cursor c = YOUR_DATABASE.doYourQuery(...);
        if (c != null) {
          // Ensure the cursor window is filled
           c.getCount();
           c.registerContentObserver(mObserver);
        }

        c.setNotificationUri(getContext().getContentResolver(), getUri());
        return c;
    }
};
}

After the code that will change DB, add

 getContentResolver().notifyChange(
            Uri.parse("content://same_with_first_string"), null);

Rusell

Answer 3

how about having a boolean in shared preferences as false .. updating the content when that boolean is true.... and when any of the operations which changes the underlying database .. that boolean will be set to true and as shared preferences you a changelistener you can recieve changes live directly after the relevant methods are called

Quinquevalent