What is getContentResolver().call() and how to use it

Question

I have read the documentation on the Android ContentResolver

I have also searched for a suitable example to no avail.

According to the documentation, there is a method call that can be used as a way to get access to custom provider methods when the standard content provider methods are insufficient:

final Bundle     call(Uri uri, String method, String arg, Bundle extras)
Call a provider-defined method.

so in my code I execute:

getContentResolver().call(uri, method, arg, extras);

but it always returns null bundle. In fact, the method in the provider never gets called.

Further research points to a (perceived) discrepancy of the contract where the RESOLVER has a uri argument with no equivalent PROVIDER parameter:

Bundle   call(String method, String arg, Bundle extras)
Call a provider-defined method.

I am obviously not understanding something. Can anyone point me in the correct direction?

Answer 1

Further research points to a discrepancy of the contract where the RESOLVER has a uri argument with no equivalent PROVIDER parameter

That's the way they wrote it. The Uri is simply to identify the ContentProvider -- the ContentProvider knows who it is and therefore does not need the Uri.

the provider method does not allow @Override annotation

Yes, it does, as you can see in this sample ContentProvider:

  @Override
  public Bundle call(String method, String arg, Bundle extras) {
    if (SET_KEY_METHOD.equals(method) && arg != null) {
      key=arg;
    }

    return(null);
  }

However, your build target (e.g., in Eclipse, Project > Properties > Android) must be set to API Level 11 or higher.

The corresponding call() from the client looks like:

getContentResolver().call(Provider.Constants.CONTENT_URI,
                          Provider.SET_KEY_METHOD, "sekrit", null);

Yes. I have a method in the provider that is declared 'public' that is passed into the contentresolver argument 'method.'

That's not how it works. call() on ContentResolver calls call() on your ContentProvider.

Answer 2

To answer your second question, my guess is that the ContentProvider version of call() does not need a Uri argument because, unlike a ContentResolver, it doesn't need to find a ContentProvider; it calls the method on itself.