What is a ContentProvider and what is it typically used for?

Copied from https://developer.android.com/guide/topics/providers/content-provider-basics.html

Provide a way to share data with other apps. We can think ContentProvider as a wrapper of database adapter. When you want to access data in a ContentProvider, you have to use the ContentResolver object to communicate with the ContentProvider object.

The ContentProvider object receives data requests from clients, performs the requested action, and returns the results：insert, delete, update, query, call (call a provider-defined method. This can be used to implement interfaces that are cheaper and/or unnatural for a table-like model.)

public class MyContentProvider extends ContentProvider
    Uri insert(Uri uri, ContentValues values);
    int delete(Uri uri, String selection, String[] selectionArgs);
    int update(Uri uri, ContentValues values, String selection, String[] selectionArgs);
    Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder);
    Bundle call(String method, String arg, Bundle extras);

3rd App 通过 ContentResolver 访问：

    TASK_TABLE_URI = Uri.parse("content://"+AUTHORITY+"/"+TASK_TABLE_PATH);
    mResolver.insert(TASK_TABLE_URI, values