Develop Reference

How to correctly retrieve data?

I've done a list that shows titles, when i click on an item is opened an activity that shows the description of the element; i'm getting this description using the id of the element.
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String descrizione=mydb.getDescription(id+1,titolo.getText().toString());
}
This is the method in my database:
public String getDescription(long id,String formulario)
{
String descrizione="NADA";
SQLiteDatabase db= this.getReadableDatabase();
Cursor res = db.rawQuery( "select * from "+formulario+" where id="+id+"", null );
if(res!=null && res.getCount()>0){
res.moveToFirst();
descrizione = res.getString(res.getColumnIndex("Descrizione"));
res.close();
}
return descrizione;
}
THE PROBLEM: when i delete an element all the description result shifted forward. I don't know if the problem is with the cursor, the item's id acquisition or with the delete method... any help is valued
This is my delete method:
public Integer deleteFormula (String formula, String formulario)
{
SQLiteDatabase db = this.getWritableDatabase();
return db.delete(formulario, "Formule = ? ", new String[] { formula});
}

First off, when you want to show database data in a ListView, you should use CursorAdapter to bind database data with your ListView. From the code you've posted, can't tell whether and how it's been implemented. If you have any doubts about it I suggest you look into this article which explains this subject very well https://github.com/codepath/android_guides/wiki/Populating-a-ListView-with-a-CursorAdapter
Secondly, when you successfully bind the data to your ListView, then in onItemClick method you can use the second parameter which is View and represents the clicked ListView row , to retrieve the data that is shown in that row.
Thirdly, when you delete a row from your database table, you should synchronize your ListView by getting a new cursor and calling your CursorAdapter changeCursor method with new cursor as argument.
This is just a rough sketch, but I hope it will help at least a little bit.

Cursor adapter would be the optimal solution. But if you want to stick with the same code when you delete a row from your database table you must ensure that you also get the updated list of data from your database.
And also you don't have to add + 1 to this code. If you have to add + 1 it means you're doing things wrong.
String descrizione=mydb.getDescription(id+1,titolo.getText().toString());
This would work well if you are just constantly updating your list with the data from your database whenever there are changes, and id doesn't represent the databaseID as it represents the ID of the view within the adapter.

Your issue is using position to determine id in :-
String descrizione=mydb.getDescription(id+1,titolo.getText().toString());
At first, assuming 3 columns inserted:-
First column has an id of 1, 2nd 2 and 3rd 3. So initially if rows are sorted according to id (good chance of this happening but no guarantee) then position 0 (first row displayed) + 1, will display data for id 1, position (2nd item in the List) 1 will show data for id 2 etc and all looks good.
However if you delete id 2 then:-
The 1st item in the list will display data from id 1 and position 0 still equates to id 1.
However the 2nd Item in the list will display data from the table for row id 3 BUT position 1 + 1 = 2 so the wrong id is calculated.
In short you cannot use position to correlate to the id.
You need to somehow get the appropriate row. Perhaps the easiest solution is to use a CursorAdapater, then id will be the id (column name must be _id).

Unable to delete pages when using FragmentStatePagerAdapter - What is the usual behavior of row ID's when integer primary key is used?

Please feel free to skip to the question as this background understanding may not be necessary for you.
I am new to android and sqlite and I am designing an app which has a content provider to access an sqlite database with multiple tables. There are several activities which use different adapters to display info from the database to the UI (i.e. cursor adapters, fragment state page adapter and array adapters). I have been having issues with the delete function in all of my activities which don't use the cursor adapter. When I try to update or delete a row from a table it deletes the wrong row or it doesn't delete anything at all. I believe it is a problem with the adapter where I am trying to figure out which row it is to send the correct info to the content provider.
The identical java code works perfectly with the cursor adapter and the rows delete normally and the other CRUD operations work. The insert and query functions work normally for all tables.The provider code uses a switch statement for each table but it is basically identical for each Uri case. All of the tables have _id as the integer primary key which is NOT set to auto increment. Since I don't fully understand how the row id works my java code does not reflect it and I keep having these issues. Although I have read many documents about content providers, adapters, sqlite databases, etc. certain key details are not clear to me.
My question is how does the row id get assigned numbers in the database when it is set to _id column as a primary key and what happens to those numbers when the database is changed?
For example, say I have an empty database. Initially after inserting the first row, the Uri will return a path segment for the 0 row and the adapter position would be 0... what would the row id for the database be (0 or 1) ?
Then for each row I insert, I know that row number would increase by one integer. Say I insert 4 rows - 0,1,2,3. Now when I am ready to delete - should the last path segment on the Uri be one integer less than the row number (i.e do I send a Uri with a last path segment of 2 to delete row 3)? Finally, after deleting, will the row ids then automatically get re-assigned so that row 4 now becomes row 3 ? Is there some code that I need to write to make that happen in the database? The primary keys are not set to auto increment.
I have different adapters and activities to where I can not access the actual database row ID once the data is displayed in the UI, so I am using the adapter position as a surrogate. This is why I am having trouble with update and delete.
Thank you very much if you read this entire question and take the time to answer it, it would help me tremendously.
I have an activity that is tabbed and uses FragmentStatePagerAdapter that is populated by a database. Here is the Adapter that I adjusted to keep track of the rows:
**EDITED:**
public class TankSectionsPagerAdapter extends FragmentStatePagerAdapter {
private ArrayList<Fragment> tankFragments = new ArrayList<>();
private ArrayList<String> tankTitles = new ArrayList<>();
//I added this ArrayList below to store the tankIDs to match the Fragments//
**public ArrayList<Integer> tankIDs = new ArrayList<>();**
public TankSectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
return tankFragments.get(position);
}
#Override
public int getCount() {
return tankFragments.size();
}
#Override
public String getPageTitle(int position) {
return tankTitles.get(position);
}
public void addPage(Fragment fragment, String tankName) {
tankFragments.add(fragment);
tankTitles.add(tankName);
// I added this below so the ID position would match each fragment position //
**tankIDs.add(tankId);**
notifyDataSetChanged();
}
// Finally I added this method below to the adapter//
** public ArrayList<Integer> getPageId(){
return tankIDs;
}**
Here is the activity where the method is called and where it pulls the data from the cursor to pass to the Adapter. There is a loop where each row creates a page(tab) in the ViewPager:
public class MyClass extends Tank implements TabLayout.OnTabSelectedListener, LoaderManager.LoaderCallbacks<Cursor> {
public TankSectionsPagerAdapter tankSectionsPagerAdapter;
TabLayout tabLayout;
private ViewPager mViewPager;
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_class);
mViewPager = (ViewPager) findViewById(R.id.container);
addPages(mViewPager);
tabLayout = (TabLayout) findViewById(R.id.tabLayout);
tabLayout.setupWithViewPager(mViewPager);
tabLayout.addOnTabSelectedListener(this);
}
public void addPages(ViewPager mViewPager) {
tankSectionsPagerAdapter = new TankSectionsPagerAdapter(getSupportFragmentManager());
mViewPager.setAdapter(tankSectionsPagerAdapter)
try {
...
Cursor cursor = getContentResolver().query(MyProvider.CONTENT_URI_TABLE_TANK_SETUP, MyDatabaseHelper.ALL_TABLE_TANK_SETUP_COLUMNS, tankDataFilter, null, null);
if (cursor.moveToFirst()) {
do {
tName = cursor.getString(cursor.getColumnIndex(MyDatabaseHelper.TANK_NAME)); ...
// all the variables are stored in the bundle passed to the fragment/
...
**tankSectionsPagerAdapter.addPage(MainTankFragment.newInstance(tankBundle),tName, int tankID);**
tankDataFilter = tankDataFilter + (-1);
}
while (cursor.moveToNext());
cursor.close();
} else {
Toast...
}
} catch (Exception e) {
Toast..
}
}
...
// Get Row ID from cursor(tankID), parameter in addPage() above//
//Get ID's from Adapter //
** ArrayList <Integer> pageID= tankSectionsPagerAdapter.getPageId();**
This is the Activity with Spinner to choose the rows/fragments to edit or delete.
public class EditTank extends Tank implements LoaderManager.LoaderCallbacks<Cursor>
...
// Get the ArrayList//
ArrayList<Integer> IDtags =getIDIntent.getIntegerArrayListExtra("tank_edit_key");
loadEditTankSpinnerData();
////***Here is the Spinner. Use row ID from the ArrayList******
Note: Don't use the id of the spinner
editTankSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
#Override
public void onItemSelected(AdapterView<?> parent, View view int position, long id) {
*** tankID = IDtags.get(position); ***
}
private void loadEditTankSpinnerData() {
List<String> tankNames = new ArrayList<String>();
Cursor cursor = getContentResolver().query(MyProvider.CONTENT_URI_TABLE_TANK_SETUP, MyDatabaseHelper.TANK_NAMES, null, null,null);
try{
if (cursor.moveToFirst()) {
do {
tankNames.add(cursor.getString(1));
} while (cursor.moveToNext());
cursor.close();
} else {
deleteTankBtn.setEnabled(false);
editTankBtn.setEnabled(false);
Toast...
}
} catch (Exception e) {
Toast...
}
...
}
The above code worked well with CursorAdapter but not with the fragmentStatePagerAdapter (***Prior to the edits it did not work, now it works well and deletes correctly).
I spent days(weeks) on this because I didn't understand why the rows weren't deleting. I hope this helps someone.

Word of advise - Try to write your question as simple as possible also the code. You shouldn't share too much code in here. People will just ignore.
You're using a CursorLoader but not using it properly. Use the LoadFinished method's cursor data.
Then you can directly pass the cursor to your FragmentPageAdapter and use it directly there.
Hope this helps.

Thanks to #pskink, #CL, and #albeee - this is what I learned from you guys and my own research.
In order to delete rows from database which is populating FragmentStatePagerAdapter or ArrayAdapter you have to be able to link the correct row with what is being displayed in the adapter. Otherwise the rows won't delete or will be inconsistent or incorrect. The CursorAdapter will automatically handle the watching for changes and selecting the ID for you. If you can use CursorAdapter or a direct onItemClickListener and get the id directly from the AdapterView with getSelectedId() or just long ID, then that is a good way to get the row ID. However, if you are getting the id indirectly by other means then you have to handle the associations...
1.You should not use the adapter position, spinner position or even spinner id to select the row. These are useful only to determine which item/fragment you want. Only the ID of the OnClickListener on the item itself will consistently give the correct row.
2.The database rows behave as such - the integer primary key will auto increment even if AUTOINCREMENT is not chosen, but the row ID's are stable once assigned. This means that each new row will have a higher ID than the last but if you delete rows in between, it will not change the IDs of the remaining rows. So the rows will skip and not be consecutive when there are edits and deletions. For this reason you must have a method to link the item to the ID permanently. There may be a better way to do this, however, I will edit the code above to show one way that I was able to do it for the FragmentStatePagerAdapter so the user can add and delete fragments dynamically.

Including Row ID from MySQL Table in Android ListView (for each list item)

When I grab info from a database (I am using MySQL), I'd like to also grab the id of the row and somehow assign it to each row of the 'listView`.
For example, let's say there is a table called fruit. fruit_id of 16 is orange. When the listView displays the list of fruit, and user clicks on a row that shows orange, i'd like to be able to access the fruit_id(16) of that row. But I'm not sure where to "hide" it.
Doing some initial research it seems there are multiple ways one can do this. The simplest might be something with using a tag, is this the best way? if so, how can you assign an id to it?

Create a class named Fruit.
class Fruit {
private int fruit_id;
private String fruit_name;
// Constructors
// Getters and Setters
}
Use an ArrayAdapter<Fruit> as the ListAdapter for your ListView. Then at ListView's onItemClickListener, get the Fruit object and get its id.

If you're using an ArrayAdapter to back your ListView, then #jaibatrik's suggestion is definitely a good one. However, if you're using a CursorAdapter, it's probably easier to exploit the return value of getItemId().
By default, a CursorAdapter will look for a column with the name "_id" in the Cursor you supply it and return that as id value whenever you click an item:
onItemClick(AdapterView<?> parent, View view, int position, long id)
That last value will contain the id of your cursor item. You can also override this behaviour and have it return any other unique value you may have access to in the Cursor.
The same is also true for an ArrayAdapter: by default it will return the position of the item in the array as unique id. However, you could easily make it return fruit_id for every item by overriding that method. Then it'll be passed in the onItemClick(...) directly, which saves you retrieving it (again) in there.
My questions is, if I grab, for example, item_id (not just item),
where do I put item_id in the listView rows (on Android side)?
The beauty of having objects that represent the data you're visualising in the list, is that you already have all the ingredients to make it work. Let's take the Fruit example given by #jaibatrik and add one getter for the sake of this example:
class Fruit {
private int fruit_id;
private String fruit_name;
// Constructors
// Getters and Setters
public int getId() { return fruit_id; }
}
In the comments you're describing you retrieve the fruit data from the database and populate it in a list:
List<Fruit> fruits = ...
That list should be the dataset backing your ArrayAdapter. To be more specific, since it's a typed class, you should have an ArrayAdapter<Fruit> instance that you set as adapter to the ListView.
Now, assuming you have an OnItemClickListener set against the ListView, it will fire whenever the user taps on an item. Using the parameters passed into the callback, you can retrieve the item that is associated with the position that was selected:
#Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Fruit fruit = (Fruit) parent.getItemAtPosition(position);
int fruit_id = fruit.getId();
...
}
With the object retrieved, you can do anything you like with the data it holds. No need to explicitly set the id against the row views, since it should already be part of the dataset that backs the ListView.

Display part of a string in layout

I am reading data from an SQLite database using a cursor and using an adapter to display it in a listView. This works fine but I now want to reduce the amount of data that I show in the listView. At the moment it displays the following:
John Smith, 25, Moday, Consultation, Dr. Harley
Jane Doe, 41, Wednesday, Surgery, Dr. Pope
What I want it to display is:
John Smith, 25, Mo, Con, Harley
Jane Doe, 41, We, Sur, Pope
Basically I want to parse 3 of the strings. The problem is the cursor adapter takes the columns of the database as a string array in its constructor so I don't know where to perform the parsing operation on it. I've tried a number of different options and am getting unrecognised column id errors and other runtime errors. Can anyone point me in the right direction?
The method where the adapter is created:
private void fillList() {
Cursor c = db.getApts();
startManagingCursor(c);
String[] from = new String[] {ModuleDB.KEY_AptCode,
ModuleDB.KEY_AptName,
ModuleDB.KEY_AptAge,
ModuleDB.KEY_AptDay,
ModuleDB.KEY_AptType,
ModuleDB.KEY_AptDoc};
int[] to = new int[] {R.id.Aptcode_entry,
R.id.AptName_entry,
R.id.AptAge_entry,
R.id.Aptday_entry,
R.id.Apttype_entry,
R.id.Aptdoc_entry};
SimpleCursorAdapter aptAdapter =
new SimpleCursorAdapter(this, R.layout.apt_entry, c, from, to);
setListAdapter(aptAdapter);
}

1.) Let your activity implement - ViewBinder
2.) Match your column and use substring
public class YourActivity extends Activity
implements SimpleCursorAdapter.ViewBinder {
adapter.setViewBinder(this); //Put this line after your list creation and setlistAdapter
#Override
public boolean setViewValue(View view, Cursor cursor, int column) {
//Showing for day, similarly for others
int dayColumn = cursor.getColumnIndex(your day column name in quotes);
if (column == dayColumn ) {
String dayString = cursor.getString(dayColumn );
((TextView)view).setText(bodyString.subString(0, 3));
return true; // Return true to show you've handled this column
}
return false;
}
}
Also - #Simon is Right - Using a Custom Adapter that extends a Cursor Adapter is always better because you get a lot more freedom to modify it later if your requirements evolve further. Off the top of my head here is an example of how you can use custom adapter and build a nice list- http://www.androidhive.info/2012/02/android-custom-listview-with-image-and-text/

Not sure what adapter you use, but assuming all the data is shown as single row then I'd extend that one and override toString() method of it.

Don't think you can override toString() on a simple adapter but perhaps this will help?
SimpleCursorAdapter aptAdapter= new SimpleCursorAdapter(this, R.layout.apt_entry, c, from, to);
CursorToStringConverter stringConverter = new CursorToStringConverter() {
#Override
public CharSequence convertToString(Cursor cursor) {
return "Hello listview"; // whatever string you want to build using cursor.getString() etc
}
};
aptAdapter.setCursorToStringConverter(stringConverter);
[EDIT] Just checked the docs and SimpleCursorAdapter does not have a toString() method, nor do any of it's super classes.

ContentProvider - returning multiple Cursors or custom Object

I have a working implementation of a ContentProvider loading data via CursorLoader into a listview (with custom CursorAdapter). It's a list of events. Every item has a title, place, etc. but also a set of offers which should be displayed in a LinearLayout inside every list row.
The problem is that a Cursor row can only contain flat data, not a set of other items.
My only idea is to make a joined query on database like this:
SELECT * FROM events, offers WHERE events.id=offers.event_id;
But then I'll have as much rows as there are offers (and the list should display events, so it's not good) and the list would be overpopulated. Maybe there is a possibility to tell CursorAdapter to only populate list rows with unique events.id but somehow retrieve the offers data as well?
The best solution would be to put a Cursor or custom Object containing offers inside the events Cursor. But afaik it's not possible.

I was facing the same problem. In fact, I think a lot of people are.
The whole mechanism of URI - to Relational DB through contentprovider, and everything that was built around it (like the various change listeners, file and stream handling) - this is all very impressive and useful, but for very simple data models.
Once your application needs a more elaborate data model, like - a hierarchy of tables, object relational semantics - this model breaks.
I've found a bunch of ORM tools for Android, but they seem too 'bleeding edge' to me (plus, for the life of me, I couldn't figure out if they have data change notification support).
ORM is very common today, I really hope the Android folks agree and add ORM capabilities to the platform.
This is what I ended up doing:
A cursor of cursors, with a a leading index cursor that helps choose the correct internal curosr.
It's kind of a temp solution, I just needed to move on with my code and get back to this later. Hope this helps.
Of course if you use a listview, you probably need to also create a custom adapter to inflate the correct views, and do the binding.
public class MultiCursor implements Cursor {
private final String TAG = this.getClass().getSimpleName();
ArrayList<Cursor> m_cursors = new ArrayList<Cursor>();
Map<Long, CursorRowPair> m_idToCursorRow = Collections.synchronizedMap(new HashMap<Long, CursorRowPair>());
Set<Long> m_idSet = new HashSet<Long>();
Cursor m_idCursor;
/**
* #precondition: _id column must exist on every type of cursor, and has to have index of 0 (be the first)
* #param idCursor
*/
public MultiCursor(Cursor idCursor) {
m_idCursor = idCursor;// this cursor binds the order (1,2,3) to ids
// go over all the ids in id cursor and add to m_idSet
initIdSet();
// m_cursors.add(idCursor);
// m_position = -1;
}
private void initIdSet() {
m_idSet.clear();
long id;
m_idCursor.moveToPosition(-1);
while (m_idCursor.moveToNext()) {
id = m_idCursor.getLong(m_idCursor.getColumnIndex(ContentDescriptor.ShowViewItem.Cols.ID));
m_idSet.add(id);
}
m_idCursor.moveToFirst();
}
public void addCursor(Cursor cursor) {
// when something changes in the child cursor, notify parent on change, to notify subscribers
// cursor.registerContentObserver(new SelfContentObserver(this)); // calls my onchange, which calls the ui
m_cursors.add(cursor);
updateIdToCursorMap(cursor);
}
private class CursorRowPair {
public final Cursor cursor;
public final int row;
public CursorRowPair(Cursor cursor, int row) {
this.cursor = cursor;
this.row = row;
}
}
private void updateIdToCursorMap(Cursor cursor) {
// get object_type
// for each row in cursor, take id, row number
// add id, <cursor,rowNum> to map
long id;
int row = 0;
cursor.moveToPosition(-1);
while (cursor.moveToNext()) {
id = cursor.getLong(cursor.getColumnIndex(ContentDescriptor.ShowViewItem.Cols.ID));
if (m_idSet.contains(id)) m_idToCursorRow.put(id, new CursorRowPair(cursor, row));
row++;
}
cursor.moveToFirst();
}
private Cursor getInternalCursor() {
if (getPosition() < 0 || getCount()==0) return m_idCursor; // todo throw a proper exception
// get the id of the current row
long id = m_idCursor.getLong(m_idCursor.getColumnIndex(ContentDescriptor.BaseCols.ID));
CursorRowPair cursorRowPair = m_idToCursorRow.get(id);
if (null == cursorRowPair) return null;
Cursor cursor = cursorRowPair.cursor;
int row = cursorRowPair.row;
cursor.moveToPosition(row);
return cursor;
}
// //////////////////////////////////////////////
#Override
public void close() {
Log.d(TAG, "close");
for (Cursor cursor : m_cursors) {
cursor.close();
}
m_idCursor.close();
}
#Override
public void copyStringToBuffer(int columnIndex, CharArrayBuffer buffer) {
Log.d(TAG, "copyStringToBuffer");
getInternalCursor().copyStringToBuffer(columnIndex, buffer);
}
etc etc etc.

In you're adapter query the offers cursor for all records and make it a class variable. Then in your getView use the event id to iterate through the offer cursor and add the necessary textviews to your row layout when it find an appropriate match. It's not elegant, but it should work.

Unfortunately one CursorLoader can only load one Cursor. So the solution was to write a custom AsyncTaskLoader which returned two Cursors.