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;
}
Related
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).
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.
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);
}
});
Currently I can check/uncheck the checkboxes by groupPosition and childPosition, and it's working fine. I save the groupPosition and childPosition to the SQLite Database.
When I added the delete option, my checkbox checked states are off/messed up.
For example, I have the following:
Group1,
Child1, Child2, Child3
I check all 3 of them and save the checked positions to the SQLite Database.
The checked positions would be 0,0 and 0,1 and 0,2 in the Database.
After I deleted Child1,
Child2 becomes position 0, Child3 becomes position 1 which would mess up the checked states.
I am trying to find a way to save the group name and child name instead of the positions to the SQLite Database, then load those names in Oncrete method.
MainActivity:
if(category_array.get(groupPosition).subcategory_array.get(childPosition).selected) {
category_array.get(groupPosition).subcategory_array.get(childPosition).selected = false;
try{
MySQLITE_DATABASE.deleteRows(groupPosition, childPosition);
}
catch (Exception e) {}
}
else
{
category_array.get(groupPosition).subcategory_array.get(childPosition).selected = true;
MySQLITE_DATABASE.addRow(groupPosition, childPosition);
}
Adapter code:
private List<Category> mGroupCollection;
if(mGroupCollection.get(groupPosition).subcategory_array.get(childPosition).selected) {
childHolder.checkBox.setBackgroundResource(R.drawable.checkbox_checked);
} else {
childHolder.checkBox.setBackgroundResource(R.drawable.checkbox_unchecked);
}
Date Holder Classes:
public class Category {
public String category_name = null;
public String cat_SelectedChildCount_name;
public ArrayList<SubCategory> subcategory_array = new ArrayList<SubCategory>();
}
//==============================
public class SubCategory {
public String subcategory_name = null;
public boolean selected = false;
}
I want to save the group name and child name instead of positions to the SQLite Database and then load them in OnCreate method.
I have tried this but it is not working:
String Group_Name = category_array.get(Integer.parseInt(groupPosition)).category_name;
String Child_Name = category_array.get(Integer.parseInt(groupPosition)).
subcategory_array.get(Integer.parseInt(childPosition)).subcategory_name;
if(category_array.get(Group_Name).subcategory_array.get(Child_Name).selected) {
category_array.get(Group_Name).subcategory_array.get(Child_Name).selected = false;
MySQLITE_DATABASE.DeleteRow(Group_Name, Child_Name);
}
else {
category_array.get(Group_Name).subcategory_array.get(Child_Name).selected = true;
MySQLITE_DATABASE.AddRow(Group_Name, Child_Name);
}
I know that I need to change the code in the adapater, data holder classes, and mainactivity in order to make it work, but I am out of ideas. I have been thinking and thinking, but nothing works...
Can someone please please guide me on this?
I am sorry for the long code.
Thank you and thank you.
Try any of the following if it suit's your requirement.
If you want to use the position strictly (May be there is no unique option)
Keep the DB design like
| id | parent_position | child_position |
Assume you have N childs. If you delete a child (Suppose it's 0). do this
Update all the child's with (child_position = child_position - 1) whose position is greater than
the deleted child of the parent. So the position remains unchanged.
Personally i would suggest don't use the position if a delete option is there. Option that i found, But don't know your use case
If you are loading the list from the database use the database primarykey as the key to save it in the SQLite database on selection/unselection. In this case you don't want to know the parent position as well.
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.