Add helper contentObservable for contentObserver

[HTChang]

Add an helper function

ContentObservable.fromContentObserver(contentResolver, watchUri, schedulerHandler)

that makes the ContentObserver as an Observable

[JakeWharton]

Just throw

[HTChang]

Thanks for reminder.

[JakeWharton]

This would need a test. Not sure how to do it with Robolectric, but with an integration test you can extend ProviderTestCase2.

[ronshapiro]

Can you use Build.VERSION_CODES.JELLY_BEAN instead of 16?

[JakeWharton]

Saw this too, but doesn't this project build with 4.0 because it's not an Android module?

[ronshapiro]

Meh, you're right. That's annoying. I guess this could be reversed to SDK_INT > VERSION_CODES.ICE_CREAM_SANDWICH_MR1, not sure if that feels weird though.

[JakeWharton]

There's a 4.1.1.4 in Maven Central that can be used to get JELLY_BEAN

[ronshapiro]

ShadowContentObserver#dispatchChange might be a good place to look for tests.

[JakeWharton]

Yeah, but Robolectric :(

[wuman]

An improved version here wuman@c85d2ff. Didn't want to send a separate pull request because it's largely based on this PR.

Improvements include:

• Removed the need to check for api levels. For api levels below 16, the base Uri will be emitted.
• Added a unit test.
• Made the scheduler handler optional.

@HTChang Feel free to incorporate my changes as you see fit.

[HTChang]

@wuman thanks, already modified my code per your suggestion!

[artem-zinnatullin]

Damn, I just needed this too and implemented it when I saw this PR..

But, I have an addition:

ContentResolver#registerContentObserver() has parameter notifyForDescendents, which is just true in this PR, I think it should be decision of the user

From Javadoc:

@param notifyForDescendents If true changes to URIs beginning with uri
will also cause notifications to be sent. If false only changes to the exact URI
specified by uri will cause notifications to be sent. If true, any URI values
at or below the specified URI will also trigger a match.

[JakeWharton]

This has been removed as part of #172 for a future release. Consider building on SqlBrite's ability to query a content resolver (not that I'm biased...).