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.

deleting row of sqlite database using a button in each row of ListView

I have created a list view which shows the data from a database. In each row of the ListView I have added a CheckBox, a button to delete it and another to edit it.
My problem is to get the id over the row, in which a button is clicked and how to convert and use that id for my sqlite database command ?
Setting a long click listener has been a bit trouble since the rows do not respond to long click when there is a CheckBox in them , so i want the buttons to exist and function.
Thanks

At first i describe the structure of the codes and then the solution i found.
the application consist of a main activity which contains the ListView. Then there is a class of SqliteOpenHelper which handles the database and there is a TaskProvider class containing the setter and getter methods of variables in the database and a TaskAdapter which is the custom adapter for the ListView.
The problem that i was facing was the fact that i couldn't address a specific row by a button existed in that row. Here is how i did it :
first in the SqliteOpenHelper class, a method is created to contain the where clause and the SqliteDataBase.delete method
public void deleteTask (SQLiteDatabase db , String deleted){
String selection = Contracts.achieveTaskClass.ID+" LIKE ?";
String[] selectionArgs = {deleted};
db.delete(Contracts.achieveTaskClass.ACHIEVETASK_TABLE,selection,selectionArgs);
}
Then in the getView method of adapter class , the button which is set to delete the row is found and the following setOnClickListener is added:
objectHolder.taskDeleteButton = (Button) row.findViewById(R.id.list_view_delete_button);
objectHolder.taskDeleteButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String deleted;
deleted = ((TaskProvider) getItem(position)).getId();
Sqldb sqldb = new Sqldb(getContext());
SQLiteDatabase db = sqldb.getReadableDatabase();
sqldb.deleteTask(db,deleted);
}
});

SQLite Database Rowid sorted

I have a delete Row function as according:
public boolean removeData(int position) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME, COL_ID+"="+position, null);
return true;
}
This function deletes a row according to its unique ID.
How can I change this so that after deleting a row, all rows below that one will be moved up to fill the empty space in the database?

That's against the design principle of a relational database. The rows are not ordered in a predictable way. So after delete you can only be sure that the deleted record appears to be away, but you have no control on the physical locations of any record, including which record(s), if any, now cover the space of the deleted one.
Querying data is another topic. You can specify a sort order, available as a parameter with the query methods. When querying your table, the results will appear exactly as you want it: If previously your results were Adam, Eve, Jack, Michael, then after deleting Jack, the result will be Adam, Eve, Michael.

The interplay between the displayed list, the domain objects behind that list, and the database is a different topic. Here are a few code snippets I use for a similar task. The basic idea is, when reading the objects that will be displayed, to include the database id with the object. So, if I read a list of products, the the domain class Product will have an id field that gets set with the database id when reading it.
To get the domain object displayed at a specific list position (e.g. the one where a user hit a delete button), the code fragment is.
public void onClick(View view) {
Product product = (Product) ProductList.this.products.get(ProductAdapter.this.listView.getPositionForView((View) view.getParent()));
... now do whatever is necessary to delete the product, probably
calling a DAO class that deletes the object based on its id,
not the list position
ProductAdapter.this.notifyDataSetChanged();
}

Solved this by removing the row in the database by the text of the TextView in the ListView instead of removing by the position of the TextView.
Now looks like this:
//Erasebutton listener
final Button eraseButton = (Button) findViewById(R.id.eraseButton);
assert eraseButton != null;
eraseButton.setOnClickListener(new View.OnClickListener() { //erasebutton onclick
public void onClick(View eraseButton) {
SparseBooleanArray checked = questionList.getCheckedItemPositions();
for(int i = questionList.getCount() - 1; i >= 0; i--)
{
if(checked.get(i)) {
//What to do with selected listitems
TextView tv = (TextView) questionList.getChildAt(i).findViewById(R.id.checkedTextView1);
db.removeData(tv.getText().toString());
}
}
checked.clear();
Cursor newCursor = db.getData();
adapter.swapCursor(newCursor);
}
});
And removeData function now looks likte this:
public boolean removeData(String question) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME, COL_QUESTION+"='"+question+"'", null);
return true;
}

expandablelistview checkboxes not staying checked

I am using a local sqlite db that is saving everything properly. When I open up a group in the expandableListView, all the checkboxes that have been stored in the db the check box is checked. When I edit an entry(I used an AlertDialog), close the group and then reopen the group. The checkbox is no longer checked. I checked the db and the edit was saved. If I go to another page and come back, once I click on the group, the child item I edited is once again checked. I used breakpoints in eclipse and it seems to find the data in the db, but not mark the box as checked. Any ideas?
This is the image of when I first click on the group(Engine)
Now I am using an AlertDialog to update the entry
Now I close the group
When I reopen the box by Battery is no longer checked.
Here is the code for when I open a group
public void onGroupExpand(int groupPosition)
{
db= new InspectionRecordsTableDBAdapter(getBaseContext());
db.open();
int inspectionId = com.signalsetapp.inspectionchecklist.report
.returnStringID();
String [] child=kids[groupPosition];
ArrayList<Color> secList = new ArrayList<Color>();
for(int i=0; i<child.length;i++)
{
try {
if (db.childFound(inspectionId, child[i]))
secList.add(new Color(child[i], true));
else
secList.add(new Color(child[i], false));
} catch (Exception e) {
secList.add(new Color(child[i], false));
e.printStackTrace();
}
}
}
and here is the update code the save into the db. This does save properly into the db
db.editRecords(
primaryId,
com.signalsetapp.inspectionchecklist.report
.returnStringID(),
parent[groupPosition],
kids[groupPosition][childPosition],
input.getText().toString(), status);
onExpand=true;

You should requery() your group cursor after you save to the database and it should regenerate the list views ( or the asynchronous equivalent since requery has been deprecated).