reading the date from sqlite in android - android-sqlite

Question

I am storing some date in sqlite and when I try to retrieve data, it is returning null.
private ArrayList<String> file_list = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ArrayList<String> _list = db.get_file
(String.valueOf(myFiles.get(position).getId()), file_list);
Log.e("TAG","_list " + _list);
case R.id.get_file:
boolean save_file = db.add_file(String.valueOf(myFiles.get(position).getId()),
file_list);
if (save_file){
Toast.makeText(this, "saved successfully", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(this, "saved failed", Toast.LENGTH_SHORT).show();
}
public ArrayList<String> get_file(String id, ArrayList<String> arrayList){
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT " + COL_FILE + " FROM "
+TABLE_NAME+" WHERE " + _ID +" =? " , new String[] {String.valueOf(id)});
if(cursor.moveToFirst()){
return arrayList;
} else {
return null;
}
}
public TrackGroupArray read_tga_file(String id, TrackGroupArray tga)
{
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT " + TGA_FILE + " FROM "
+TABLE_NAME+" WHERE " + _ID +" =? " , new String[] {String.valueOf(id)});
if(cursor.moveToFirst()){
return tga;
} else {
return null;
}
}
TrackGroupArray read_tga = db.read_tga_file(String.valueOf(myFiles.get(position).getId()),
trackGroupArray);
Every time I save a file, it is saved successfully, I have checked in the db and the file is there. But when I want to retrieve it, Log.e("TAG","_list " + _list); returns null.

Answer 1

Your get_File method, even if there is a row and the moveToFirst succeeds, will always return null as in the event that a row is located/selected you do nothing other than return an un-instantiated arrayList.
You need to
a) instantiate the arrayList (otherwise it will be null) and then
b) add elements to the arrayList for each row that exists if any.
So something like :-
#SuppressLint("Range")
public ArrayList<String> get_file(String id, ArrayList<String> arrayList) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT " + COL_FILE + " FROM "
+ TABLE_NAME + " WHERE " + _ID + " =? ", new String[]{String.valueOf(id)});
ArrayList<String> rv = new ArrayList<>(); //<<<<< A instantiate the ArrayList<String>
/* Loop through the returned row(s) if any */
while (cursor.moveToNext()) {
/* for each iteration add an element to rv (the ArrayList) */
rv.add(cursor.getString(cursor.getColumnIndex(COL_FILE)));
}
cursor.close(); //<<<<< should ALWAYS close Cursors when done with them
return rv; // return the arraylist
}