android content provider AUTHORITIES – Stack Overflow
The Authority is used to interact with a particular content provider, that means it must be unique. That’s why is a good practice to declare it as your domain name (in reverse) plus the name of the package containing the provider, that way is less likely that other developer creates an app with a content provider declaring the same authority.
You declare it in the manifest so your app and other apps (if you let them) can manipulate data through your content provider in the form of a uri:
content://authority-name/data-in-the-provider
It works similar to domains in http urls:
http://domain-name/data-in-the-site
What does nullColumnHack means?
original source : http://stackoverflow.com/questions/32774507/what-does-nullcolumnhack-means
nullColumnHack optional; may be null. SQL doesn’t allow inserting a completely empty row without naming at least one column name. If your provided values is empty, no column names are known and an empty row can’t be inserted. If not set to null, the nullColumnHack parameter provides the name of nullable column name to explicitly insert a NULL into in the case where your values is empty.
SQLiteOpenHelper obj의 getWritableDatabase () 을 통해 얻어진 SQLiteDatabase obj의 method인 insert() 함수에 두번째 파라미터로 nullColumnHack을 지정할수 있다. empty row가 전달되었을때 여기에 지정된 칼럼을 null로 설정함으로써 다른 빈 칼럼들이 들어간 row를 추가 할수 있게 된다.