Develop Reference

Android notifyDataSetChanged behave differently

I have two different applications, that update a list in both cases.
App1
addButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
dataList.add("NEW CITY");
cityAdapter.notifyDataSetChanged();
}
});
Here, my floating action button, update the list with const string (as test input). If I don't use notifyDataSetChanged the list will not show the 'NEW CITY' text.
App2
This one is a bit more complex than the App1, because now use a fragment to add/edit city.
The two listeners looks like this.
addCityButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
new AddCityFragment().show(getSupportFragmentManager(),"ADD_CITY");
}
});
cityList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
#Override
public boolean onItemLongClick(AdapterView<?> adapterView, View view, int i, long l) {
City clickedCity = cityAdapter.getItem(i);
AddCityFragment.newInstance(clickedCity, i).show(getSupportFragmentManager(),
"EDIT_CITY");
return false;
}
});
I have two methods that implement the logic which are invoked when the fragment is loaded.
#Override
public void onOkPressListener(City newCity) {
dataList.add(newCity);
}
#Override
public void onEditPressListener(City editCity, int index) {
City currentCity = dataList.get(index);
currentCity.setCity(editCity.getCity());
currentCity.setProvince(editCity.getProvince());
}
For some reason, the list updates (add/edit) even though I didn't call notifyDataSetChanged in each method. Is the list refreshed somehow when the fragment is closed? I feel like I ignore some sort of a Android activity lifecycle method here.

recyclerview item mishap(undesirable behaviour) in android studio

I have a recycler view with a list of items and each of those items have checkboxes attached to them. When a checkbox is checked, it behaves properly and there is no problem with unwanted items getting checked. But when a checked item is deleted, then the unwanted item gets checked.
My Adapter Class :
public class TaskAdapter extends RecyclerView.Adapter<TaskAdapter.TaskHolder> {
private static List<Task> tasks = new ArrayList<>();
private static OnItemClickListener listener;
private static TaskAdapter adapter = new TaskAdapter();
#NonNull
#Override
public TaskHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.task_item, parent, false);
return new TaskHolder(itemView);
}
#Override
public void onBindViewHolder(#NonNull TaskHolder holder, int position) {
Task currentTask = tasks.get(position);
holder.a_tname.setText(currentTask.getTname());
holder.a_tdate.setText(currentTask.getTDate());
holder.a_ttime.setText(currentTask.getTTime());
holder.a_tprior.setText(currentTask.getTprior());
holder.bind(tasks.get(position));
holder.bind2(tasks.get(position));
}
#Override
public int getItemCount() {
return tasks.size();
}
public void setTasks(List<Task> tasks) {
this.tasks = tasks;
Collections.sort( tasks, Task.comparepriority);
notifyDataSetChanged();
}
public Task getTaskAt(int position){
return tasks.get(position);
}
class TaskHolder extends RecyclerView.ViewHolder {
private final TextView a_tname;
private final TextView a_tdate;
private final TextView a_ttime;
private final TextView a_tprior;
ImageView priorityIndicator;
CheckBox checkbox;
public TaskHolder(View itemView) {
super(itemView);
a_tname = itemView.findViewById(R.id.a_tname);
a_tdate=itemView.findViewById(R.id.a_tdate);
a_ttime = itemView.findViewById(R.id.a_ttime);
a_tprior = itemView.findViewById(R.id.a_tprior);
priorityIndicator = itemView.findViewById(R.id.priorityIndicator);
checkbox = itemView.findViewById(R.id.checkbox);
itemView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
int position = getAdapterPosition();
if(listener!=null&&position!=RecyclerView.NO_POSITION){
listener.onItemClick(tasks.get(position));
}
}
});
}
private void bind(Task task){
int drawableId;int red = R.color.red;int yellow = R.color.yellow;int green = R.color.green;
int color1 = ContextCompat.getColor(a_tprior.getContext(), red);
int color2 = ContextCompat.getColor(a_tprior.getContext(),yellow);
int color3 = ContextCompat.getColor(a_tprior.getContext(),green);
switch(task.t_prior){
case "1": drawableId = R.drawable.ic_baseline_priority_high_24;
a_tprior.setTextColor(color1);
break;
case "2": drawableId = R.drawable.ic_baseline_priority_middle_24;
a_tprior.setTextColor(color2);
break;
case "3" : drawableId = R.drawable.ic_baseline_low_priority_24;
a_tprior.setTextColor(color3);
break;
default: drawableId = R.drawable.ic_baseline_crop_square_24;
}
priorityIndicator.setImageDrawable(ContextCompat.getDrawable(priorityIndicator.getContext(),drawableId));
}
public void bind2(Task task){
final boolean[] checked = {true};
checkbox.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(checkbox.isChecked()) {
String pos = Integer.valueOf(getAdapterPosition()).toString();
PreferenceManager.getDefaultSharedPreferences(checkbox.getContext()).edit().
putBoolean("checkbox" + pos , checked[0]).apply();
Toast.makeText(checkbox.getContext(), "Way to go! Now swipe to delete", Toast.LENGTH_LONG).show();
}
else {
checked[0] =false;
String pos = Integer.valueOf(getAdapterPosition()).toString();
PreferenceManager.getDefaultSharedPreferences(checkbox.getContext()).edit().
putBoolean("checkbox" + pos, checked[0]).apply();
}
}
}); String pos = Integer.valueOf(getAdapterPosition()).toString();
boolean cb = PreferenceManager.getDefaultSharedPreferences(checkbox.getContext()).getBoolean
("checkbox" + pos, false);
checkbox.setChecked(cb);
}
}
public interface OnItemClickListener {
void onItemClick(Task ta);
}
public void setOnItemClickListener(OnItemClickListener listener){
this.listener = listener;
}
}
My code to delete in HomeFragment.java -
new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0,
ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {
#Override
public boolean onMove(#NonNull RecyclerView recyclerView, #NonNull
RecyclerView.ViewHolder viewHolder, #NonNull RecyclerView.ViewHolder target) {
return false;
}
#Override
public void onSwiped(#NonNull RecyclerView.ViewHolder viewHolder, int direction) {
int position = viewHolder.getAdapterPosition();
new AlertDialog.Builder(getActivity())
.setMessage("Do you want to delete this task?")
.setPositiveButton("Delete", ((dialog, which) ->
taskViewmodel.delete(adapter.getTaskAt(viewHolder.getAdapterPosition()))))
.setNegativeButton("Cancel", ((dialog, which) -> adapter.notifyItemChanged(position)))
.setOnCancelListener(dialog -> adapter.notifyItemChanged(position))
.create().show();
}
}).attachToRecyclerView(recyclerView);
Edit : I guess the problem is with the code associated with saving the state of the checkbox because the checkbox at a particular item position is checked so when the item is deleted, the below item takes its place and so it gets checked. Suppose item at 2nd position is checked, and I delete that item, then the item at the 3rd position takes its place and so that gets checked. I need to know how to resolve this.May i know what changes should i make to rectify this problem?
Thankyou

back at the day, there was no delete intuition, now since you're storing the state of whether an item checked or not in SharedPreferences using its position, if you have 3 items where position =2 is checked, and you delete this checked item at pos=2, then the third item would take its place behaving as new item at pos=2, that's why when you delete one, all checked states will get shifted.
I guess there's no option here but to use some identifier in your Task class, where one Task is uniquely identified using this number/string and you use that unique identifier to store the items state in your SharedPreferences as a key.
a quick cheap way to do it is to make Task class behave like how Room database identify its automatic unique int/long identifiers.
the way to do it is by
defining a static int/long counter field in your Task class that identifies how many ids you used so far so to not repeat any id that was taken before (even if it was deleted and not used now)
define a private int/long id field in the Task class, while in the Task class constructor when you're initializing a new Task you would increment the static counter field and use this new value as a value for your private id for your newly created Task.
N.B : you shouldn't increment the static value and assign a new id for every created task if the one you're creating an object for is an old one that you retrieved from SharedPreferences/Database that already have an old id, for that case you might have two constructors one that accepts an old id as paramter and one that increments the taskCounter and get a new id, you might also have two constructors that one calls the other incase you have some other paramteres you're passing to the task object at creation and you want to avoid duplicating code in both constructors.
that way when you're checking status using SharedPreferences for some task, you would use the private id value of Task instead of its position.
your Task class might look like this (in case of two constructors without any additional code in the constructor):
public class Task {
public static int tasksCounter =0;
public int taskId ;
...
//constructor for a new Task
public Task(){
this.taskId= ++tasksCounter ;
}
//constructor for an old Task
public Task(int oldId){
this.taskId= oldId ;
}
your Task class might look like this (in case of two constructors and you want to avoid code dublication):
public class Task {
public static int tasksCounter =0;
public int taskId ;
//you'd call that one if you're creating a completely new Task and it will call
the other constructor for you
public Task(){
Task(++tasksCounter)
}
//you'd call that one if you're creating a Task that you already have an id for
public Task(int id){
this.taskId= id ;
//some other code here
}
and in your adapter when you ask about whether its checked or not it would be like this :
PreferenceManager.getDefaultSharedPreferences(checkbox.getContext()).getBoolean
("checkbox" + task.taskId, false);
and when you the checkbox status get changed you'd change its value in preferences likewise using the task.taskId instead of position.
that of course would raise another problem that every time you start your application that static field will get reset to 0 again.
so you should store its value too in sharedpreferences maybe either
when you create a new Task, its value will be incremented so you should store the new value
or
just before the activity or fragment getting destroyed by overriding the method onDestroy() in either the activity or the fragment, you should store the last value it had
and when you start your activity or fragment you need to fetch it from sharedpreferences and assign it to Task.tasksCounter.
N.B : just incase you don't know, you get the value of static field by calling the class it self and you don't need to create a new object of this class to get its value, calling the next code is sufficent to get and edit its value :
Task.tasksCounter
and at the end,
since you have your complex data now (Task class), I would highly suggest to stop using SharedPreferences for storing everything and you start reading and switching to Room Database
Room Database provides you with necessary storing abilities of a Database including :
having an autoincrement identifier without having you worried about their values
storing and getting your data with just one line of code with a simple query instead of calling get with keys a 100 times.
with changing your Task class into an entity that have an autoincrement field you'll be good to go and ready to use Room to store your tasks.

I am not much familiar with lambda function so I am sharing how I would have did the same task.I tried this code for my own app and it worked perfectly fine.
Check the below code:
#Override
public void onSwiped(#NonNull RecyclerView.ViewHolder viewHolder, int direction) {
int position = viewHolder.getAbsoluteAdapterPosition();//getAdapterPosition is depreciated, use getAbsoluteAdapterPosition
AlertDialog.Builder builder = new AlertDialog.Builder(getContext());
builder.setMessage("Do you want to delete this task?");
builder.setPositiveButton("Delete",new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
taskViewmodel.delete(adapter.getTaskAt(viewHolder.getAdapterPosition()))
adapter.notifyItemRemoved(position);
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
builder.setOnCancelListener(new DialogInterface.OnCancelListener() {
#Override
public void onCancel(DialogInterface dialog) {
adapter.notifyItemChanged(position);
}
}).show();
}
}).attachToRecyclerView(recyclerView);

Unable to refresh listView from other class

In my main fragment, I have a listView called notesListView. noteAdapter populates notesListView. When user long clicks on one of the notesListView's elements, a dialog shows up and asks if user really wants to remove an item. If he agrees, then that item is removed from the database. If not - then life goes on.
The issue is that my Dialog is other class (other Fragment). For this class, I pass my database object and noteAdapter object as well, so it could remove item from database and then notify noteAdapter that data has changed. Sounds good enough, but it doesn't work, and I have absolutely no idea why. Give it a look please and help me out.
This is a method in mainFragment, which handles the mentioned listView:
public void handleNotes(final ListView notesListView) {
if (database.getNoteCount() != 0) {
notesListView.setAdapter(noteAdapter);
notesListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
#Override
public boolean onItemLongClick(AdapterView<?> adapterView, View view, int i, long l) {
TextView textViewId = (TextView) view.findViewById(R.id.textViewId);
DeleteNoteFragment newFragment = new DeleteNoteFragment(database, noteAdapter, Integer.parseInt(textViewId.getText().toString()));
newFragment.show(getActivity().getSupportFragmentManager(), "deleteConfirmation");
return false;
}
});
}
}
As you can see, DeleteNoteFragment is being created and then shown.
Lets look at DeleteNoteFragment itself:
public class DeleteNoteFragment extends DialogFragment {
private Database database;
private NoteAdapter noteAdapter;
private int i;
public DeleteNoteFragment(Database database, NoteAdapter noteAdapter, int i) {
this.database = database;
this.noteAdapter = noteAdapter;
this.i = i;
}
#NonNull
#Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
// Use the Builder class for convenient dialog construction
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setMessage(R.string.dialog_delete_note)
.setPositiveButton(R.string.dialog_delete_confirm, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
database.removeNote(i);
noteAdapter.notifyDataSetChanged();
Toast.makeText(getActivity(), "Note deleted successfully!", Toast.LENGTH_LONG).show();
}
})
.setNegativeButton(R.string.dialog_delete_denny, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
// User cancelled the dialog
}
});
// Create the AlertDialog object and return it
return builder.create();
}
}
Maybe you can spot where I am making a mistake, or got any tips how to solve this issue?

You are deleting the data in database but not in the adapter:
database.removeNote(i);
noteAdapter.notifyDataSetChanged();
Creates a method in the adapter to get the list that you have in the adapter. Something like:
database.removeNote(i);
noteAdapter.getListOfItems().remove(i);
noteAdapter.notifyDataSetChanged();

notifyDataSetChanged - "Notifies the attached observers that the underlying data has been changed and any View reflecting the data set should refresh itself." It doesn't reload data from database. You still have to remove the item from the adapter by calling remove method and then call notifyDataSetChanged

How to get setMultiChoiceItems checkboxes in dialogs to update when you use a Sqlite Cursor

When implementing setMultiChoiceItems with a cursor, you have to specify an isCheckedColumn.
The problem, as articulated on other sites, is that when users select an item from the list the checkbox does not update. Some have suggested updating the SqLite table each time a user selects an item, but this did not work in my application. Here is the solution I came up with.

This is what I came up with:
#Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
int myDialogChoice = getArguments().getInt("whichDialog");
mSelectedItems = new ArrayList(); // Where we track the selected items
mCurrentFavoritesSelection = new ArrayList();
myDataBaseAdapter = new AthleteDbAdapter(getActivity());
// int myAthleteId;
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
switch(myDialogChoice) {
case Select_From_Favorites:
myCursorFromSqLite = myDataBaseAdapter.fetchAllFavorites(getActivity());
// You need a Primative Boolean Array to specify which items were selected last time.
boolean[] booleanPrimativeArray = new boolean[myCursorFromSqLite.getCount()];
final ArrayList mArrayListOfIDs = new ArrayList();
ArrayList<Boolean> myBooleanList = new ArrayList<Boolean>();
// This array will be the choices that appear in the Dialog.
ArrayList<String> mArrayListOfNames = new ArrayList<String>();
myCursorFromSqLite.moveToFirst();
/* Populate Arrays
*
*/
int iCount = 0;
while(!myCursorFromSqLite.isAfterLast()) {
// put _id's from SqLite data into an array.
mArrayListOfIDs.add(Integer.valueOf(
myCursorFromSqLite.getString(myCursorFromSqLite.getColumnIndex(KEY_ROWID))));
// put series of booleans into Primative Array depending upon whether user selected them last time.
if(Integer.valueOf(myCursorFromSqLite.getString(myCursorFromSqLite.getColumnIndex("checked"))) == 1){
booleanPrimativeArray[iCount] = true;
mSelectedItems.add(
Integer.valueOf(myCursorFromSqLite.getString(myCursorFromSqLite.getColumnIndex(KEY_ROWID)))
);
// I kept track of what selections from last time were.
mCurrentFavoritesSelection.add(
Integer.valueOf(myCursorFromSqLite.getString(myCursorFromSqLite.getColumnIndex(KEY_ROWID)))
);
} else booleanPrimativeArray[iCount] = false;
iCount++;
mArrayListOfNames.add(myCursorFromSqLite.getString(myCursorFromSqLite.getColumnIndex("fullName")));
myCursorFromSqLite.moveToNext();
}
// Change the ArrayList of names to a Char Sequence
CharSequence[] charSeqOfNames = mArrayListOfNames.toArray(new CharSequence[mArrayListOfNames.size()]);
try{
myCursorFromSqLite.close();
} catch (Throwable t) {
Log.e(APP_TAG,"Error closing myCursorFromSqLite Cursor " + t);
}
builder.setTitle(R.string.pick_athletes)
.setMultiChoiceItems(charSeqOfNames, booleanPrimativeArray,
new DialogInterface.OnMultiChoiceClickListener() {
#Override
public void onClick(DialogInterface dialog, int which,
boolean isChecked) {
if (isChecked) {
// If the user checked the item, build an array containing the selected items _id's.
mSelectedItems.add((Integer) mArrayListOfIDs.get(which));
} else if (mSelectedItems.contains((Integer) mArrayListOfIDs.get(which))) {
// Else, if the user changes his mind and de-selects an item, remove it
mSelectedItems.remove((Integer) mArrayListOfIDs.get(which));
}
}
})
// Set the action buttons
.setPositiveButton(R.string.pullathletesbutton, new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int id) {
// User clicked OK, so save the mSelectedItems results somewhere
// or return them to the component that opened the dialog
Log.d(APP_TAG,"Call something");
mListener.onDialogPositiveClick(PickListDialog.this, mSelectedItems, mCurrentFavoritesSelection);
}
})
.setNegativeButton(R.string.cancelbutton, new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int id) {
}
});
This worked well. The user can change his mind without affecting the underlying database and the checkmarks update properly. Once the user has finalized his choices, he hits the "positive" button and the database is updated.

Android Spinner - onItemSelected / setOnItemSelectedListener not triggering

This is driving me nuts since it's something I've done before but can't figure out why it isn't working now...
I've got a menu button, implemented in the usual way via a menu.xml file and the onOptionsItemSelected method with a switch in it, that creates and displays a spinner.
I've added the setOnItemSelectedListener, but it never seems to trigger. The spinner appears, I pick an option or back out, neither onItemSelected or onNothingSelected are called.
Here is all the code between the "case" and "return true" of the menu-button-handling switch statement. (topThis is a variable referring to the context of the activity - works fine for all other toasts in the app)
String[] widgetModes = {"Mode 1", "Mode2"};
ArrayAdapter<String> widgetModeAdapter = new ArrayAdapter<String> (this, android.R.layout.simple_spinner_item, widgetModes);
widgetModeAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
Spinner widgetModeSpinner = new Spinner(this);
widgetModeSpinner.setAdapter(widgetModeAdapter);
widgetModeSpinner.setPrompt("Choose Widget Mode");
widgetModeSpinner.setOnItemSelectedListener(new OnItemSelectedListener()
{
#Override
public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id)
{
Toast.makeText(topThis, "derp", Toast.LENGTH_LONG).show();
}
#Override
public void onNothingSelected(AdapterView<?> parentView)
{
Toast.makeText(topThis, "herf", Toast.LENGTH_LONG).show();
}
});
widgetModeSpinner.performClick();
Any ideas? I vaguely suspect that the fact I'm creating the Spinner programmatically is the problem...

I had the similar problem when I was implementing a spinner, I resolved it by getting the parent View and set Adapter-
spinner1 =(Spinner)findViewById(R.id.spinner1);
spinner1.setAdapter(BindSpinner("ProgramMaster",cols,null,true,""));
spinner1.setOnItemSelectedListener(new OnItemSelectedListener()
{
protected Adapter initializedAdapter=null;
#Override
public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id)
{
if(initializedAdapter !=parentView.getAdapter() ) {
initializedAdapter = parentView.getAdapter();
return;
}
String selected = parentView.getItemAtPosition(position).toString();
if(abc.equals("Select") && !selected.equals("Select"))
{
do something
}
else
{
Do something
}
textQualification=selected;
SearchUpdated("Qualification");
}
#Override
public void onNothingSelected(AdapterView<?> parentView) {
// your code here
}
});

Remember that you can't re-select the same spinner item, it always sets the first item as selected if you are not adding some custom code to handle the spinner selection.
For the Toast not showing, I would suggest to always use the "MyActivity.this" as your context when creating a Toast inside a listener interface like this:
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
/**
* Called when a new item is selected (in the Spinner)
*/
public void onItemSelected(AdapterView<?> parent, View view,
int pos, long id) {
// An spinnerItem was selected. You can retrieve the selected item using
// parent.getItemAtPosition(pos)
Toast.makeText(MyActivity.this, "Hello Toast",Toast.LENGTH_SHORT).show();
}
public void onNothingSelected(AdapterView<?> parent) {
// Do nothing, just another required interface callback
}
}); // (optional)
And the .show() at the end is easy to forget sometimes;)

Actually, if your spinner visibility is set to gone then it will trigger the click of it when you call performclick() method but it will not trigger its setOnItemSelectedListener
so you need to change the visibility then it will work

I know the question is a bit old, but in case you are waiting for a AsyncTask callback, make sure that you let your adapter know of the data changes by calling notifyDataSetChanged() on the callback thread!
#Override
public void onPostExecute(String result) {
///do something with your data
spinnerArrayAdapter.notifyDataSetChanged();
}