SimpleAdapter needs an _id field

问题

I got this :

Cursor c = db.query("Org", null, null, null, null, null, null);

which means I choose a table "Org", but together with this I need to make this :

 Cursor c = db.rawQuery(" SELECT "+ id + " AS _id")

because SimpleAdapter need to have an _id field necessarily for some reason or it will crash with an error. How do I combine this 2 into one query?

回答1:

For your statement : Cursor c = db.query("Org", null, null, null, null, null, null); the second parameter is wrong, you shoukd mention the column names in it.

public Cursor query (boolean distinct, String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit)

Whereas for,

Cursor c = db.rawQuery(" SELECT "+ id + " AS _id from Org"); 

means that you Select id and create an alias of it using AS into _id, and you are selecting this id from Org table. so now you will be able to access the result from this query from the column name _id, and in order to access the result use:

c.moveToFirst();    
while (c.moveToNext())
{
 System.out.println(c.getString(c.getColumnIndex("_id")); 
}

回答2:

The second parameter of the query function is the list of columns. If you want to rename a column, you cannot just blindy return all columns but have to list the desired columns:

String[] columns = new String[] { id+" AS _id", "Name", "Color", "whatever..." };
Cursor c = db.query("Org", columns, null, null, null, null, null);

来源：https://stackoverflow.com/questions/25752193/simpleadapter-needs-an-id-field