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How do I create a new object on every button click?

I am creating a notes app, and I've all but finished it. My app starts on the main activity, which shows a recylcerView displaying all of the saved notes. To create a new note, you press a button, which sends you to another activity where you write your note. You then press a button that saves the note as an instance of the Note class and sends that object instance back to the main activity where it updates the recyclerView.
My problem is, every time I press the save button for my note, it just updates the Note instance instead of creating an entirely new one. How do I get it to create a new instance of the Note class so that I can have more than one saved note?
Here is my code for the save button:
Intent intent = new Intent(AddNoteActivity.this, MainActivity.class);
String mTitle = title.getText().toString();
String mContent = content.getText().toString();
intent.putExtra("notePar", new Note(mTitle, mContent));
startActivity(intent);
Here is my code for the mainactivity:
Intent intent = getIntent();
Note sentParcNote = intent.getParcelableExtra("notePar");
if(sentParcNote != null) {
notes.add(sentParcNote);
}

You are using startActivity(intent) to navigate from AddNoteActivity to MainActivity, this method is used to start a new activity, which means, the system will create a new instance of MainActivity class and put it at the top of the activity stack. This way you will always have 0 or 1 note (when sentParcNote != null)
I would suggest to use startActivityForResult when you navigate from MainActivity to AddNoteActivity and call setResult in your AddNoteActivity
Example:
MainActivity:
Declare this static int at the top of your class (e.g: just before onCreate method)
private static final int ADD_NOTE_ACTIVITY_REQUEST_CODE = 2;
Then add this piece of code on your button action to start AddNoteActivity:
Intent addNoteIntent = new Intent(this, AddNoteActivity.class);
startActivityForResult(addNoteIntent, ADD_NOTE_ACTIVITY_REQUEST_CODE);
Then to catch the new note from AddNoteActivity
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == ADD_NOTE_ACTIVITY_REQUEST_CODE) {
if (resultCode == RESULT_OK) {
Note sentParcNote = data.getParcelableExtra("notePar");
if(sentParcNote != null) {
notes.add(sentParcNote);
}
}
}
}
AddNoteActivity:
add this piece of code to your save button action
String mTitle = title.getText().toString();
String mContent = content.getText().toString();
Intent intent = new Intent();
intent.putExtra("notePar", new Note(mTitle, mContent));
setResult(RESULT_OK, intent);
// finish closes the current activity which means in this case it goes back to the MainActivity
finish();
I would suggest using local storage to save your notes otherwise if you restart the app you will always have 0 notes.

Starting an Activity from a Notification and passing data onBackPressed

I have 3 Activities on the app:
MainMenuActivity -> ExecuteTrainingActivity -> ExecuteExerciseActivity.
From MainMenuActivity to ExecuteTrainingActivity, I'm passing an idExecution and an idExercise for ExecuteTrainingActivity query and load the initial data.
ExecuteTrainingActivity onCreate:
#Override
protected void onCreate(Bundle savedInstanceState) {
//...
initialize();
setupRecyclerView(exercises);
}
private void initialize() {
Bundle extras = getIntent().getExtras();
if (extras != null) {
if (extras.containsKey("id_execution")) {
idExecution = extras.getLong("id_execution");
idExercise = extras.getLong("id_exercise");
execution = queryExecution(idExecution);
} else {
insertExecution();
}
}
}
In the 3rd activity, ExecuteExerciseActivity, I have a TimerFragment that, and when TimerCountdown reaches 0, it opens a Notification popup, that when clicked open an fresh ExecuteExerciseActivity.
On this TimerFragment, I'm passing as Extras the same ids, so I can get them in the new fresh ExecuteExerciseActivity:
public class TimerFragment extends Fragment {
//...
private void showNotification(){
Intent intent = new Intent(getActivity(), ExecuteExerciseActivity.class);
intent.putExtra("id_execution", idExecution);
intent.putExtra("id_exercise", idExercise);
intent.putExtra("position", position);
TaskStackBuilder stackBuilder = TaskStackBuilder.create(getActivity());
stackBuilder.addNextIntentWithParentStack(intent);
PendingIntent pendingIntent = stackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);
/*=== CHECK IF NOTIFICATION CHANNEL IS ACTIVE ===*/
boolean ok = isNotificationChannelEnabled(getActivity(), Constants.CHANNEL_ID);
NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(requireNonNull(getActivity()), Constants.CHANNEL_ID)
.setSmallIcon(R.drawable.d77)
.setContentTitle("Teste Notificação")
.setContentText("Ababa")
.setPriority(NotificationCompat.PRIORITY_HIGH)
.setContentIntent(pendingIntent)
.setAutoCancel(true);
NotificationManagerCompat notificationManager = NotificationManagerCompat.from(getActivity());
notificationManager.notify(0, mBuilder.build());
}
From this new fresh ExecuteExerciseActivity, I want to make the system maintain the same navigation flow of Activities, but when I backpress from the new ExecuteExerciseActivity to ExecuteTrainingActivity, i can't pass the Id's for the ExecuteTrainingActivity query and load.
Is there a way to pass arguments onBackPress?
Is the best approach override onBackPress creating a new intent and a starting a new Activity?
**My manifest is using parentActivityName correctly.

Save your query and id into a SharedPreferences in onDestroy of your ExecuteExerciseActivity then pull out the query and id again in the old ExecuteTrainingActivity. onBackPressed triggers onDestroy event of an activity's life cycle. Then in the onResume of ExecuteTrainingActivity pull this data back out.

I think you can achieve this by overriding onOptionsItemSelected() method of ExecuteExerciseActivity. Try this:
#Override
public boolean onOptionsItemSelected(MenuItem item) {
if (item.getItemId() == android.R.id.home) {
Intent intent = new Intent(this, ExecuteExerciseActivity.class);
//Add the extras to the intent
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
finish();
return true;
}
return super.onOptionsItemSelected(item);
}

In Android, if your Activity starts another Activity and want to pass data to that Activity, you would add those data as Intent extras.
This Activity A to Activity B type of sending data is something you're using already.
But for Activity B back to Activity A, there's actually a built-in solution for this, which is through startActivityForResult(Intent, REQUEST_CODE) instead of startActivity(Intent).
Now in Activity B, you simply have to code:
#Override
public void onBackPressed()
{
Intent resultIntent = getIntent();
resultIntent.putExtra(EXTRA_NAME, extra_value);
setResult(Activity.RESULT_OK, resultIntent);
finish();
}
Basically, in Activity B, you're setting the data you want to send back to the Activity A that started Activity B, since there's a connection between these two Activities.
Next, in your Activity A, just override the onActivityResult() method.
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == REQUEST_CODE) {
if (resultCode == RESULT_OK) {
// get data through data.getIntExtra() and etc
}
}
}
The request code needs to match the REQUEST_CODE you used for Activity B, so Activity A knows which Activity to respond to. The result code is just a quick way for you to categorize the type of result you're getting back from Activity B, since there might be more than one type of result being returned from Activity B.
This solution of passing data is better than creating a new Intent and starting a new Activity because you don't need to start a new Activity. Your Activity A already exists, so there's no reason to rebuild the entire layout, reload all the data, and have a new Activity existing on the Activity stack.
Since your only intention is to pass data from Activity B back to the Activity A that started it, use startActivityForResult() and onActivityResult() to handle this type of data sharing.

Updating some fields in main activity after exiting from another activity

My MainActivity has an EditText with the hint "Weight (lb)", as well as a button that goes to the SettingsActivity. In SettingsActivity, the user is able to change the units used from US to metric. Upon exiting SettingsActivity via the built-in back button on the phone, I want the hint for the EditText to immediately change from "Weight (lb)" to "Weight (kg)".
The farthest I've gotten is using the onBackPressed() method in SettingsActivity. The button press is detected, and the code inside it is executed, but I don't want to change anything related to MainActivity's inside the SettingsActivity class.
Is there an on___() method that I should be using here that I don't know about? Any help would be appreciated.

You can use startActivityForResult for SettingsActivity and after that handle the return result as:
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == PICK_CONTACT_REQUEST) {
// Make sure the request was successful
if (resultCode == RESULT_OK) {
// The user picked a contact.
// The Intent's data Uri identifies which contact was selected.
// Do something with the contact here (bigger example below)
}
}
More detail: https://developer.android.com/training/basics/intents/result.html

You can use startActivityForResult for SettingsActivity and after that handle the return result as:
In your MainActivity:
public static int CALL_SETTINGS = 1000;
startActivityForResult(new Intent(this,SettingsActivity.class),CALL_SETTINGS);
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == PICK_CONTACT_REQUEST) {
// Make sure the request was successful
if (resultCode == RESULT_OK) {
// The user picked a contact.
// The Intent's data Uri identifies which contact was selected.
// Do something with the contact here (bigger example below)
}
}
In your Settings Activity:
on backpressed write this:
Intent returnIntent = new Intent();
returnIntent.putExtra("result",data);
setResult(Activity.RESULT_OK,returnIntent);
finish();

Easy option is to store the waitUnit in shared preference and on OnResume() of the Main activity read it from there and update the widget.
You can update the preferences in your Settings activity like below:
preferences = context.getSharedPreferences(context.getString(R.string.preference_file_key),
Context.MODE_PRIVATE);
preferences.edit().putString("unit", "kg");
And you can read this changed value in OnResume() of your Main Activity
preferences.getString("unit", "default unit")

Communication between running activities?

I'm new to android and is currently developing a quest/tresurehunt application. It is a prototype and is going to be evaluated in the field and i would therefore like to implement some sort of cheat to skip checkpoints if the application should crash during the tests.
My application work the way that when you select a quest a activity will be loaded to handle all checkpoints and the user location(ActivityAdapter.java). This activity will open the diffrent navigation tool activities and pass information to them based on the next checkpont using intent. I have implemented a long press event in the app i would like to activate the skip/cheat. My problem is that i can't figure out how to do this.
Location changed event of ActivityAdapter.java:
public void onLocationChanged(Location location) {
location.distanceBetween(location.getLatitude(), location.getLongitude(), lat, lng, dist);
if (dist[0]<= 10) {
if (cid == checkpoints.size()) {
Intent intent = new Intent(ActivityAdapter.this, SuccessActivity.class);
intent.putExtra("title", checkpoints.get(cid).get("title"));
startActivity(intent);
} else {
new loadAndStartQuest().execute();
}
}
}
loadAndStartQuest() just find the next checkpoint and start the right activity (navigationtool). I have tryed creating a object of the ActivityAdapter and set a variable and add it to the the if statement which did not work. I guess it is because it will create another instance of the activity and not affect the current/running one. So how would you communicate between two running activities?

To send data from Activity1 to running Activity2, you must pass through the next steps:
In Manifest.xml set launch mode "singleTask" for Activity2
<activity android:name="Activity2" android:launchMode="singleTask">
Put extras and start Activity2 from Activity1 (if Activity2 was started before, intent will be sended to existing instance).
Intent intent = new Intent(getContext(), Activity2.class);
intent.putExtra("CHECK_POINT", checkPointData);
startActivity(intent)
Override method onNewIntent() in Activity2
protected void onNewIntent(Intent intent) {
super.onNewIntent(intent);
setIntent(intent);
onNewCheckPoint();
}
private void onNewCheckPoint(){
Intent intent = getIntent();
Bundle extras = intent.getExtras();
//in this moment, you can process data, like you want.
}

How to restart activity using intent?

I am making an android app which plays mp3 files. I am launching the mp3 playing activity from within another activity using intent:
Intent intent=new Intent(ListViewA.this,mp3player.class);
intent.putExtra("feed",gh);
i.setFlags(0);
i.setPackage(null);
//intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(intent);
Now when the user selects another song from a list, I want to close the previous instance of the mp3player activity and start a new one using the intent code (above). How do I go about doing that? Thanks.

Instead of startActivity use startActivityForResult(intent, PLAY_SONG) then you can call finishActivity(PLAY_SONG) where PLAY_SONG is a constant number.
class member
private static final int PLAY_SONG
And then
finishActivity(PLAY_SONG);
Intent intent=new Intent(ListViewA.this,mp3player.class);
intent.putExtra("feed",gh);
i.setFlags(0);
i.setPackage(null);
startActivityForResult(intent, PLAY_SONG)

Hey its very simple Instead of calling Intent from Mp3Playeractivity call finish() when you are pressing the back button by implementing
#Override
public void onBackPressed(){
finish();
}
which will cause close your MpeplayerActivity