Android: How to create my own cursor class?

Question

I'm using Sqlite in Android and to get a value from the database I use something like this:

Cursor cursor = sqliteDatabase.rawQuery("select title,category from table", null);

int columnIndexTitle = cursor.getColumnIndex("title");
iny columnIndexCategory = cursor.getColumnIndex("category");

cursor.moveToFirst();
while (cursor.moveToNext()) {
    String title = cursor.getString(columnIndexTitle);  
    String category = cursor.getString(columnIndexCategory);    
}
cursor.close();

I want to create my own Cursor so that I can do getColumnIndex() and getString() with one method. Something like this:

String title = cursor.getString("title");

I want to create my own class that extends the cursor that I get from sqliteDatabase.rawQuery, but I'm not sure how to accomplish this. Should I extend SQLiteCursor or how should I do this? Is it even a possible and is it a good idea?

Answer 1

I came across this question looking for the best way to create a custom Cursor to use together with a SQLiteDatabase. In my case I needed an extra attribute to the Cursor to carry an additional piece of information, so my use case is not exactly as in the body of the question. Posting my findings in hope it will be helpful.

The tricky part for me was that the SQLiteDatabase query methods returns a Cursor, and I needed to pass on a custom subclass to Cursor.

I found the solution in the Android API: Use the CursorWrapper class. It seems to be designed exactly for this.

The class:

public class MyCustomCursor extends CursorWrapper {

    public MyCustomCursor(Cursor cursor) {
        super(cursor);
    }

    private int myAddedAttribute;

    public int getMyAddedAttribute() {
        return myAddedAttribute;
    }

    public void setMyAddedAttribute(int myAddedAttribute) {
        this.myAddedAttribute = myAddedAttribute;
    }

}

Usage:

public MyCustomCursor getCursor(...) {
    SQLiteDatabase DB = ...;
    Cursor rawCursor = DB.query(...);
    MyCustomCursor myCursor = new MyCustomCursor(rawCursor);
    myCursor.setMyAddedAttribute(...);
    return myCursor;
}

Answer 2

Creating your own getString will cause a map lookup for each call instead of only for getColumnIndex.

Here's the code for SQLiteCursor.getColumnIndex and AbstractCursor.getColumnIndex. If you have many rows, reducing calls to this function will prevent unnecessary string processing and map lookups.