Develop Reference

Not able to retrieve the data from database when running it on real device

I m working on an e-learning type of an application where i retrieve the data from the database on list.
It works fine on the emulator,but when i use the APK file of that app on real device,it does not show any data on list, my database is stored in the windows-file explorer-package-data-database-table_name.
I am referring to this site
http://anujarosha.wordpress.com/2011/12/19/how-to-retrieve-data-from-a-sqlite-database-in-android/
Here's a snippet of my code using database
list_adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, namelist1());
list1.setAdapter(list_adapter);
}
public List<String> namelist1()
{
// We have to return a List which contains only String values. Lets create a List first
List<String> namelist= new ArrayList<String>();
// First we need to make contact with the database we have created using the DbHelper class
Database_helper_class open_database_helper= new Database_helper_class(this);
// Then we need to get a readable database
SQLiteDatabase sqlitedatabase = open_database_helper.getReadableDatabase();
// We need a a guy to read the database query. Cursor interface will do it for us
//(String table, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy)
Cursor cursor =sqlitedatabase.query(open_database_helper.TABLE_E_LEARNING,null,null,null,null,null,null);
//above query is read all the database column
// Cursor object read all the fields. So we make sure to check it will not miss any by looping through a while loop
while(cursor.moveToNext()){
String str_name = cursor.getString(cursor.getColumnIndex(Database_helper_class.QUES_COLUMN));
String str_id = cursor.getString(cursor.getColumnIndex(Database_helper_class.ANS_COLUMN));
//double str_gpa = cursor.getDouble(cursor.getColumnIndex(Database_helper_class.GPA_COLUMN));
// Finish reading one raw, now we have to pass them to the POJO
nameclass nameclassobj1=new nameclass();
nameclassobj1.setname(str_name);
nameclassobj1.setid(str_id);
//nameclassobj1.setgpa(str_gpa);
// Lets pass that POJO to our ArrayList which contains undergraduates as type
pojo_namelist.add(nameclassobj1);
// But we need a List of String to display in the ListView also.
//That is why we create "nameList"
namelist.add(str_name);
}
sqlitedatabase.close();

sqlitedatabase.query() returns a cursor which is positioned before the first record. make sure to call moveToFirst() before trying to access any data from it.

verify your database path in DBHelper.class. And after that Write below line before you call while loop.
cursor.moveToFirst();
This will point to your first record and then your while loop will work.

Try it like this:
// Cursor object read all the fields. So we make sure to check it will not miss any by looping through a while loop
cursor.moveToFirst();
while(!cursor.isAfterLast()){
String str_name = cursor.getString(cursor.getColumnIndex(Database_helper_class.QUES_COLUMN));
String str_id = cursor.getString(cursor.getColumnIndex(Database_helper_class.ANS_COLUMN));
//double str_gpa = cursor.getDouble(cursor.getColumnIndex(Database_helper_class.GPA_COLUMN));
// Finish reading one raw, now we have to pass them to the POJO
nameclass nameclassobj1=new nameclass();
nameclassobj1.setname(str_name);
nameclassobj1.setid(str_id);
//nameclassobj1.setgpa(str_gpa);
// Lets pass that POJO to our ArrayList which contains undergraduates as type
pojo_namelist.add(nameclassobj1);
// But we need a List of String to display in the ListView also.
//That is why we create "nameList"
namelist.add(str_name);
}
Use the isAfterLast()-method to check, if your reached the end of your cursor.

Sorry for late reply, got busy in other application
Actually the data was not saved in the database, that is why i was not getting it on device.
It works now.

Android: loading from SQLite Database

So I'm still building a Database to support a project of mine. There are two different things to be saved: first, attribute values of some player objects and second, simple values stored in a java class.
ATM my problem lies in the process of loading values of a player object and writing it in the respective class.
Now let's see some code:
Following you see the method I want to use for saving the values in the database.
That works fine atm, but I just realized I'm still passing the contentValues object an extra value for the 'ID' , which I did set - and planned to keep that way - as autoincrement.
Any Idea how to work this in accordingly?
public void savePlayer(Player player[]) {
for (int i = 0; i <= 3; i++) {
playerValues.put("ID", i);
playerValues.put("Name", player[i].getName());
playerValues.put("HP", player[i].getHp());
playerValues.put("Satisfaction", player[i].getsatisfaction());
playerValues.put("Hygiene", player[i].isHygieneInt());
playerValues.put("IsAlive", player[i].isAliveInt());
}
db.insert("playertable", null, playerValues);
}
Okay, hold on to your hats because this might look a bit like spaghetti - the load-method:
public void loadPlayer() {
String[] namecolumn = { "Name" };
String[] intcolumn = { "ID, HP, Satisfaction, Hygiene, IsAlive" };
String[] namesToString = new String[4];
for (int j = 0; j <= 3; j++) {
Cursor playerCursorName = db.query("playertable", namecolumn, "ID="
+ j, null, null, null, null);
namesToString = cursorToString(playerCursorName);
Resource.playerArray[j].setName(namesToString[j]);
}
for (int i = 0; i < 3; i++) {
int[] restToInt;
Cursor playerCursorInt = db.query("playertable", intcolumn, "ID="
+ i, null, null, null, null);
restToInt = cursorToInt(playerCursorInt, 4);
Resource.playerArray[i].setHp(restToInt[i]);
Resource.playerArray[i].setsatisfaction(restToInt[i]);
Resource.playerArray[i].setHygieneInt(restToInt[i]);
Resource.playerArray[i].setAliveInt(restToInt[i]);
}
}
Yeah, I know this looks pretty ugly but let me explain it:
Because there are 4 player objects I planned on iterating through the database entries by using the ID as identifier to get exactly one row at a time and writing the name and the other values of this object in the java class where I want to manage them within my project.
Note: same problem with autoincrement here than in the save method
In addition, I get a CursorIndexOutOfBoundsException when calling loadPlayer because
Index -1 is being requested - isn't that the result of an operation on the database resulting in an error?
Yeah that's pretty much it, I'll provide you with additional code if requested, hope someone can help me

You are using Cursors in a slightly odd way here.
The point of a Cursor is to ask SQLite to do the hard work of fetching data for you, and your job is simply to use the cursor to iterate through the returned values.
Firstly, I would change the query here to ask for all values in the table (and perhaps put some condition to constrain what you get back), to make sure your cursor then contains all your values.
Then, I would loop through the cursor's values by using a while loop, (with cursor.moveToPosition(-1) before the loop) moving along the cursor by using cursor.moveToNext().
See the API for more information:
http://developer.android.com/reference/android/database/Cursor.html
With regard to the autoincrement problem, as far as I can remember you can leave out the ID and use db.insert() without that field and the database will provide an ID for you.
You shouldn't have the same issue in your load method because it doesn't make sense to autoincrement when loading, you just get back what's in the database.

What to do with Cursor after a SQLite query?

This is my first time using a database and I'm not really sure how this works. I made the database and made a query that returns a cursor and... now what? What is a cursor, really? Can I just use that to navigate through my data or do I have to put it in an ArrayList or ListActivity or what?

You need to iterate the cursor to get your results.
Use cursor.moveToFirst() and/or cursor.moveToNext() (with a while loop). Then you can use the getX() method, like cursor.getInt() or cursor.getString().
For example, ir your are expecting one result from your query:
if (cursor.moveToFirst()) {
String name = cursor.getString(cursor.getColumnIndex('NAME'));
int age = cursor.getInt(cursor.getColumnIndex('AGE'));
} else {
// oops nothing found!
}

First call cursor.moveToFirst(). Each time you call cursor.moveToNext() it will move to the next row. Make sure when you are done with your cursor you call cursor.deactivate() or you will get errors in your log cat.

Iterate over the returned Cursor instance
public List<Object[]> cursorToTableRows(Cursor cursor) {
List<Object[]> result = new ArrayList<Object[]>(cursor.getCount());
cursor.move(0);
cursor.moveToNext();
while (cursor.isAfterLast() == false) {
Object[] tableRow = new Object[cursor.getColumnCount()];
for(int i=0; i<cursor.getColumnNames().length; i++) {
int columnIndex = cursor.getColumnIndex(cursor.getColumnName(i));
String columnValue = cursor.getString(columnIndex);
tableRow[i] = columnValue;
}
result.add(tableRow);
cursor.moveToNext();
}
cursor.close();
return result;
}
Then create the desired objects.
public List<Vehicle> getVehicles() {
List<Vehicle> vehicles = new ArrayList<Vehicle>();
Cursor cursor = null;
List<Object[]> objects = cursorToTableRows(cursor);
for(Object[] row : objects) {
int i=0;
Vehicle vehicle = new Vehicle(row[i++].toString(), row[i++].toString()));
vehicles.add(vehicle)
}
return vehicles;
}

from Developer.android: This interface provides random read-write access to the result set returned by a database query.
In other words: query returns you a set of data represented by a cursor. First you need to make sure you got a valid cursor (not null) and then try to move it to desired position in the data set (use moveToXXX methods). In order to obtain data pointed by cursor use getXXX methods. When done using it make sure to call close to release resources.

According to this link it looks like you can iterate through the query return using something like:
cursor.next();
And grab the data at the location you are looking for using:
cursor.getString(0)

After you successfully have your Cursor setup, you would typically want to display that to a view in some form.
Have a look at the following answer for a detailed, but simple example of using a Cursor Adapter to pair up your newly-minted Cursor with your desired XML View:
https://stackoverflow.com/a/20532937/293280

Android: having basic problems with sqlite database

I am having some trouble implementing a sqlite database in my simple android application:
a user is displayed a list of animals in a Listview.Upon selecting an animal the user is brought to an activity "Animal",which will display a picture of the animal and give them options to
view Animal Bio
Back
All very simple so far, right?
I have working the database, which will populate the listView of animals.Database currently looks like
Table Animal-
_ID,
Name
Table Biography-
_ID,
Bio
This is where I would welcome any helpful advice on my problem, or on how to improve my implementation.
Currently populating the DB as follows
long populateDB(){
String[] animalName = {"Lion" "Zebra", "Tiger", "Gorilla",...};
String[] animalBios = {"Found in the "...}
ContentValues animalNameVals = new ContentValues();
ContentValues animalBioVals = new ContentValues();
long[] rowIds = new long[animalName.length];
// Populate the animal table
for(int i = 0; i < animalName.length; i++){
animalNameVals.put(KEY_ANIMALNAME, animalName[i]);
rowIds[i] = db.insert(ANIMAL_TABLE, null, animalNameVals);
}
// Populate the Bio table
for(int j = 0; j < bios.length; j++){
animalBioVals.put(KEY_BIO, bios[j]);
rowIds[j] = db.insert(BIOS_TABLE, null, animalBioVals);
}
return rowIds[0];
}
And had planned on being able to tell database which animal on list was selected by passing extras with the intent, eg if position on listItemClick == 1, pass in tiger and retrieve tiger bio from db.
Problems:
Then on the Animal activity page is getExtra() == tiger, telling the activity that tiger was selected from the list and to load this bio from the DB..well, I cannot see an efficient method of implementation for this idea and am struggling to do so.
My second headache comes from adding the bio to the application from the Db.Originally I had a test bio hardcoded in a string, shown in a TextView.Is there a way to retrieve a string from a cursor and add it to the TextView id?I understand I will need some adapter, what I do not understand is why cant it be as simple as setResource(R.id.bio) = bio.
Thanks you for reading and any help is much appriciated.

First problem: First of all, I'm not sure why you don't have the column Bio in the Animal-table? As no Bio would fit to any other animal than itself, you can safely do this. By doing this you can query the database upon selection and pass the entire object (including name of animal and bio) to the next Activity and use this to get your information. If this was somewhat unclear, let me know and I'll try to explain it better.
Second problem: You can get values from tables (there of also Strings) using a Cursor. To get the String you can do something like this where cursor is the Cursor with your result from the database:
String bio;
// Move Cursor to its first element
if(cursor.moveToFirst()) {
// Make sure the cursor is not null
if(cursor != null) {
bio = cursor.getString(cursor.getColumnIndex("Bio")));
}
}
Sidenote: If I read the code correctly, it seems that you use long for ID's? The usual thing to go about ID's is integers as far as I know.

Android: How to create my own cursor class?

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?

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;
}

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.

I wouldn't extend it, I'd make a helper:
class MartinCursor {
private Cursor cursor;
MartinCursor(Cursor cursor) {
this.cursor = cursor;
}
String getString(String column) {
....
}
}
or
class MartinCursorHelper {
static String getString(Cursor cursor, String column) {
....
}
}
Personally, I'd do the latter, unless you hate providing this extra argument all the time.
EDIT: I forgot to mention pydave's important point: If you call this in a loop, you're setting yourself up for a noticeable performance impact. The preferred way is to lookup the index once, cache it, and use that instead.

You should make use of the DatabaseUtils.stringForQuery() static method that is already in Android SDK to easily retrieve a value, this example is for String bot there is also method for Long
stringForQuery(SQLiteDatabase db, String query, String[] selectionArgs)
Utility method to run the query on the db and return the value in the first column of the first row.
Something like
String myString=DatabaseUtils.stringForQuery(getDB(),query,selectionArgs);

Came across this looking for a different solution, but just want to add this since I believe the answers are unsatisfactory.
You can easily create your own cursor class. In order to allow functions requiring Cursor to accept it, it must extend AbstractCursor. To overcome the issue of system not using your class, you simply make your class a wrapper.
There is a really good example here.
https://android.googlesource.com/platform/packages/apps/Contacts/+/8df53636fe956713cc3c13d9051aeb1982074286/src/com/android/contacts/calllog/ExtendedCursor.java
public class ExtendedCursor extends AbstractCursor {
/** The cursor to wrap. */
private final Cursor mCursor;
/** The name of the additional column. */
private final String mColumnName;
/** The value to be assigned to the additional column. */
private final Object mValue;
/**
* Creates a new cursor which extends the given cursor by adding a column with a constant value.
*
* #param cursor the cursor to extend
* #param columnName the name of the additional column
* #param value the value to be assigned to the additional column
*/
public ExtendedCursor(Cursor cursor, String columnName, Object value) {
mCursor = cursor;
mColumnName = columnName;
mValue = value;
}
#Override
public int getCount() {
return mCursor.getCount();
}
#Override
public String[] getColumnNames() {
String[] columnNames = mCursor.getColumnNames();
int length = columnNames.length;
String[] extendedColumnNames = new String[length + 1];
System.arraycopy(columnNames, 0, extendedColumnNames, 0, length);
extendedColumnNames[length] = mColumnName;
return extendedColumnNames;
}
That's the general idea of how it will work.
Now to the meat of the problem. To prevent the performance hit, create a hash to hold the column indices. This will serve as a cache. When getString is called, check the hash for the column index. If it does not exist, then fetch it with getColumnIndex and cache it.
I'm sorry I can't add any code currently, but I'm on mobile so I'll try to add some later.