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androidsqlandroid-cursor

When Does Query Returns Null on Android?

I don't seem to find any information on query, insert or any other SQL method returning null. But it does if error occurs.

I just wonder whether cursor being null means an error occurred or could it mean no rows were selected (for instance)? I don't know how I should treat it - as an error or something that may happen time to time.

Solution

  • I don't believe you ever need to check if(cursor == null) {}.

    First
    If your query doesn't return any rows, you will receive an empty Cursor. The Cursor will not be null.

    There are many ways to check if a Cursor is empty:

    • if(cursor.getCount == 0) {}
    • if(!cursor.moveToFirst()) {}

    In fact all of the Cursor#moveTo...() methods return either true or false, if you receive false then the row that you requested does not exist.

    Second
    If an error occurs then you need to catch the error in a try-catch block, otherwise the app will crash from an unhandled exception.

    Also insert(), update(), and delete() return an integer, not a Cursor. These methods return the number of rows affected by your statement, if no rows are affected these methods return 0.