Room persistence library and Content provider

Last Couple of days I have been spending times on learning new Android Architecture Components . After following up some blog posts, documentation & tutorials , every components were getting clear to me . But Suddenly I realised what about our old friend Content Provider . I might sound silly , because before writing this question I have spent quite a time searching , Am I be the only one came up with this question . I hadn't got any helpful solution . Anyways here is it , if I want to build up an app with local DB , I will now obviously choose new Architecture Components (live data , view model , room ) without any farther thinking this will be very helpful to make app 10x robust . But If I want my DB datas accessible to other app , for instance To Widget How do I integrate Content Provider with Room ?

I had the same question by the way. And I found a sample here which answers my question. Hope it does the same with you.

In short, this is in the DAO object which would be called from Content Provider's query() method.

/**
 * Select all cheeses.
 *
 * @return A {@link Cursor} of all the cheeses in the table.
 */
@Query("SELECT * FROM " + Cheese.TABLE_NAME)
Cursor selectAll();

Notice how it returns Cursor object. Other operations, you can see for yourself in more detail in the sample.

This here is choice number 3 in the answer by @CommonsWare, I think.

if I want to build up an app with local DB , I will now obviously choose new Architecture Components (live data , view model , room )

I would not use the term "obviously" there. The Architecture Components are an option, but not a requirement.

But If I want my DB datas accessible to other app , for instance To Widget How do I integrate Content Provider with Room ?

An app widget is unrelated to a ContentProvider. IMHO very few apps should be exposing databases to third parties via ContentProvider, and no apps should be using a ContentProvider purely for internal purposes.

That being said, you have a few choices:

1. Do not use Room, at least for the tables to be exposed via the ContentProvider

2. Use Room for internal purposes, but then use classic SQLite programming techniques for the ContentProvider, by calling getOpenHelper() on your RoomDatabase

3. Use Room in the ContentProvider, writing your own code to build up a MatrixCursor from the Room entities that you retrieve (for query()) or creating the entities for use with other operations (for insert(), update(), delete(), etc.)