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How to change the background color of a view from a different activity in android?

I am working on a Quiz app. First when a user opens the app they go to the MainActivity, from there when they press start they go to the Categories Activity , from there after selecting a category they go to the Sets Activity, from there after selecting a set the go to the Questions Activity and finally after completing all the questions they reach the Score Activity. Here in the score activity when the click on Done button they are redirected to the MainActivity. In the Score Activity i want to change the color of the Set that they completed to green instead of the default color. How can i do this? I created a sets item layout xml file and used an adapter to fill the gridview in the Sets Activity with views from the adapter. Currently i am getting a null object reference after clicking the Done button in the ScoreActivity.
Here is the code :
SetsAdapter.java
public class SetsAdapter extends BaseAdapter {
private int numOfSets;
public SetsAdapter(int numOfSets) {
this.numOfSets = numOfSets;
}
#Override
public int getCount() {
return numOfSets;
}
#Override
public Object getItem(int position) {
return null;
}
#Override
public long getItemId(int position) {
return 0;
}
#Override
public View getView(final int position, View convertView, final ViewGroup parent) {
View view;
if(convertView == null){
view = LayoutInflater.from(parent.getContext()).inflate(R.layout.set_item_layout, parent, false);
}
else {
view = convertView;
}
view.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent questionIntent = new Intent(parent.getContext(), QuestionActivity.class);
questionIntent.putExtra("SETNUM", position +1);
parent.getContext().startActivity(questionIntent);
}
});
((TextView) view.findViewById(R.id.setNumber)).setText(String.valueOf(position+1));
return view;
}
}
SetsActivity.java
public class SetsActivity extends AppCompatActivity {
private GridView sets_grid;
private FirebaseFirestore firestore;
public static int categoryID;
private Dialog loadingDialog;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sets);
Toolbar toolbar = (Toolbar)findViewById(R.id.set_toolbar);
setSupportActionBar(toolbar);
String title = getIntent().getStringExtra("CATEGORY");
categoryID = getIntent().getIntExtra("CATEGORY_ID",1);
getSupportActionBar().setTitle(title);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
sets_grid = findViewById(R.id.sets_gridView);
loadingDialog = new Dialog(SetsActivity.this);
loadingDialog.setContentView(R.layout.loading_progressbar);
loadingDialog.setCancelable(false);
loadingDialog.getWindow().setBackgroundDrawableResource(R.drawable.progress_background);
loadingDialog.getWindow().setLayout(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
loadingDialog.show();
firestore = FirebaseFirestore.getInstance();
loadSets();
}
private void loadSets() {
firestore.collection("Quiz").document("CAT" + String.valueOf(categoryID))
.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
#Override
public void onComplete(#NonNull Task<DocumentSnapshot> task) {
if (task.isSuccessful()) {
DocumentSnapshot doc = task.getResult();
if (doc.exists()) {
long sets = (long) doc.get("SETS");
SetsAdapter adapter = new SetsAdapter(Integer.valueOf((int)sets));
sets_grid.setAdapter(adapter);
} else {
Toast.makeText(SetsActivity.this, "No Sets Exists!", Toast.LENGTH_SHORT).show();
finish();
}
} else {
Toast.makeText(SetsActivity.this, task.getException().getMessage(), Toast.LENGTH_SHORT).show();
}
loadingDialog.cancel();
}
});
}
#Override
public boolean onOptionsItemSelected(#NonNull MenuItem item) {
if(item.getItemId() == android.R.id.home)
finish();
return super.onOptionsItemSelected(item);
}
}
ScoreActivity.java
public class ScoreActivity extends AppCompatActivity {
private TextView score;
private Button done;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_score);
score = findViewById(R.id.score_tv);
done = findViewById(R.id.score_activity_done);
String score_str = getIntent().getStringExtra("SCORE");
final int setNum = getIntent().getIntExtra("SetNum", 1);
score.setText(score_str);
done.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Here is the issue I am facing
View view = findViewById(R.id.setNumber);
view.setBackgroundColor(Color.GREEN);
Intent mainIntent = new Intent(ScoreActivity.this, MainActivity.class);
startActivity(mainIntent);
ScoreActivity.this.finish();
}
});
}
}

As your activity Sequence is MainActivity -> Categories -> Sets -> Scores.
You've two options to change the color with two different life cycle of the change.
To change the color on a temporary basis, this will reset itself after closing the app or resrtating the 'Sets' activity. It can be done in two ways: Using Public Static Variable and using a public function.
To change the color on a permanent basis until the app is uninstalled/reinstalled. You should use SharedPreferences. SharedPreferences acts like a private data stored in device's memory for further use and it stays there unchanged until and unless the app is removed/data is cleared. Although, apps with root permission can access any app's SharedPreferences data and can modify it as well.You can use SharedPreferences as explained here. Or, you can use some library to access it an easy way. The way I use it in all my apps is TinyDB(it's just a java/kotlin file). This works as:
//store the value from ScoreActivity after completion as
TinyDB tinyDB = TinyDB(this);
tinyDB.putBoolean("isSet1Completed",true);
//access the boolean variable in SetsActivity to change the color of any set that
//is completed and if it's true, just change the color.
TinyDB tinyDB = TinyDB(this);
Boolean bool1 = tinyDB.getBoolean("isSet1Completed");
But, it's your choice what way you want to prefer.
Now, this was about the lifecycle of the change you'll do: Temp or Permanent. Now, we'll talk about how you change the color.
Using public static variable in Sets activity. What you can do is you can set the imageView/textview whose background you want to change as public static variable. Remember, this idea is not preferred as it causes memory leak but it's just easy.
Declare it as public static ImageView imageview;(or TextView) intialize it in the
onCreated() as imageView = finViewById(R.id.viewId); in Sets activity. Call
it as new SetsActivity().imageView.setBackgroundColor(yourColor); in ScoreActivity.
Second way is to create a public function in SetsAcitvity, putting the color change code in it, and then calling it from the ScoreActivity. Just declare it as public void changeColor(){ //your work} and call it from ScoreActivity as new SetsActivity().changeCOlor(). You can also pass some arguments to the function like setId.
I've provided you every thing you need. Rest you should figure out yourself to actually learn it and not copy it.

I think simply you add flag in MainActivity.
for example, add flag in MainActivity.
boolean isFromDone = false;
and when done clicked,
done.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Here is the issue I am facing
Intent mainIntent = new Intent(ScoreActivity.this, MainActivity.class);
mainIntent.putExtra("FromDone", true);
startActivity(mainIntent);
ScoreActivity.this.finish();
}
});
and in MainActivity, add this.
#Override
protected void onResume() {
super.onResume();
isFromDone = getIntent().getBooleanExtra("FromDone", false);
if(isFromDone) {
(TextView) view.findViewById(R.id.setNumber)).setBackgroundColor(Color.GREEN);
}
}

Suppose you have a Linear Layout in Activity A and you want to change it's background color from a button click which is present in Activity B.
Step 1 Create a class and declare a static variable.
class Util { private static LinearLayout mylayout ; }
Step 2
In the activity which is holding this layout, initialize it.
Util.mylayout = findviewbyid(R.id.linear);
Step 3Change the background color on button click from Activity B
onClick{
Util.mylayout.setBackgroundColor(Color.RED);
}

Initializing variables in onCreate, but updating them in onResume()

Here is my situation:
I have an OnCreate code like the following:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bunz = Bunz.getInstance(); //getting instance of bunz
bunz.setBunz(50);
bunz.setMoney(0);
bunz.setIncrement(1);
Button upgradeButton = (Button) findViewById(R.id.upgradeButton);
upgradeButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View view){
Intent startIntent = new Intent(getApplicationContext(), UpgradeMenu.class);
startActivity(startIntent);
}
});
moneyCount = (TextView) findViewById(R.id.moneyCount);
bunzCount = (TextView) findViewById(R.id.bunzCount);
ImageButton bun = (ImageButton) findViewById(R.id.bun);
}
Notice how in my OnCreate code, I do 2 things; first, I initialize all the values I need:
bunz.setBunz(50);
bunz.setMoney(0);
bunz.setIncrement(1);
and then I display these values on TextViews and set up some Buttons and intents:
Button upgradeButton = (Button) findViewById(R.id.upgradeButton);
upgradeButton.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View view){
Intent startIntent = new Intent(getApplicationContext(), UpgradeMenu.class);
startActivity(startIntent);
}
});
moneyCount = (TextView) findViewById(R.id.moneyCount);
bunzCount = (TextView) findViewById(R.id.bunzCount);
ImageButton bun = (ImageButton) findViewById(R.id.bun);
I'm new to Android studio, and here is the problem I'm having. I want to use onResume() to update these values in the TextView (I update them in another activity) every time I go back to this activity. However, if I move all the code in onCreate into onResume, then every time I go back to this activity, the values will be set to 50,0, and 1. I understand I could use a boolean, so that onCreate() triggers the first time the app is launched, but onResume() doesn't trigger, and then onResume() triggers after that, and simply copy and paste the second half of the onCreate code into onResume(), but that seems inefficient, and isn't how Android studio is designed to work. Can I somehow initialize the values in another location?
I have a global Bunz class that looks like the following:
public class Bunz {
private int bunz;
private int money;
private int increment;
//singleton code
private static Bunz instance;
private Bunz(){
}
public static Bunz getInstance(){
if (instance == null){
instance = new Bunz();
}
return instance;
}
public int getBunz() {
return bunz;
}
public void setBunz(int num){
bunz = num;
}
public int getMoney(){
return money;
}
public void setMoney(int num){
money = num;
}
public int getIncrement(){
return increment;
}
public void setIncrement(int num){
increment = num;
}
}
so maybe I could initialize these values here somehow?
Thanks!

here's one thing you could alternatively do:
public static Bunz getInstance(){
if (instance == null){
instance = new Bunz();
instance.setBunz(50);
instance.setMoney(0);
}
return instance;
}
in your instance creation here, try setting the values you want here, instead of in onCreate of the app.
you could just be making the changes in the constructor as well.

While your code uses statics, which I believe is unnecessary. Statics are not your average goto solution, they come with a hefty price of an object not eligible for GC.
You can get the result from the second activity via onActivityResult method.
First, start second activity using startAtivityForResult() //This takes in a request code(Int), it can be whatever you set.
First activity
Intent intent = new Intent(this, SecondActivity.class);
startActivityForResult(intent , 100);
Second Activity
//Do you work in the second activity, generate new data
Intent returnIntent = new Intent();
returnIntent.putExtra("bunz", 100);
returnIntent.putExtra("money", 200);
returnIntent.putExtra("increment", 2);
setResult(Activity.RESULT_OK, returnIntent);
finish();
Capture Second Activity Result
This code is supposed to be written in your first activity.
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == 100) { //Remember the code we set in startActivityForResult? This is where we identify our work
if(resultCode == Activity.RESULT_OK){ //Code to check if data is passed
Int bunz =data.getIntExtra("bunz")
bunz.setBunz(bunz)
.....
}
}
}

Losing data when sending between two classes

My app doesn't display anything when passing data from one class to another. I located through with the debugger that my ArrayList doesn't get the right value from the class.
I'm sending data with the following function:
public class Adaugare extends AppCompatActivity {
private ListView myListView;
private NumeAdapter numeAdapter;
String inume;
int ivarsta;
Intent intent = new Intent();
private ArrayList persoanaArrayList = new ArrayList<>();
public ArrayList getPersoanaArrayList() {
return persoanaArrayList;
}
public int getPersoanaArrayListsize() {
return persoanaArrayList.size();
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_adaugare);
myListView = (ListView) findViewById(R.id.persoana_list);
Button btn_fin = (Button) findViewById(R.id.btn_fin);
btn_fin.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
EditText nume_edit_text = (EditText) findViewById(R.id.ins_nume);
EditText varsta_edit_text = (EditText) findViewById(R.id.ins_var);
ivarsta = Integer.parseInt(varsta_edit_text.getText().toString());
inume = nume_edit_text.getText().toString();
persoanaArrayList.add(new Persoana(inume, ivarsta));
}
});
}
}
And recieving it with:
public class Afisare extends AppCompatActivity {
ListView myListView;
NumeAdapter numeAdapter;
Adaugare ad = new Adaugare();
int cate;
int i;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_afisare);
myListView = (ListView) findViewById(R.id.persoana_list);
ArrayList<Persoana> persoanaArrayList = new ArrayList<Persoana>(ad.getPersoanaArrayList());
numeAdapter = new NumeAdapter(this, persoanaArrayList);
myListView.setAdapter(numeAdapter);
}
The class Persoana is:
public class Persoana {
private String nume;
private int varsta;
Persoana(String inume, int ivar) {
this.nume = inume;
this.varsta = ivar;
}
public String getNume() {
return nume;
}
public int getVarsta() {
return varsta;
}
public void setNume(String nume) {
this.nume = nume;
}
public void setVarsta(int varsta) {
this.varsta = varsta;
}
}
Persoana is the main class, everything is saved in it. ad is an object of Adaugare, Adaugare being the class from which I've taken the code for getPersoanaArrayList. At debugging some values appeared at ad, namely Adaugare #4556, and persoanaArrayList remains null.
I need the persoanaArrayList so that i can initialize my Adapter and listView. Everything else in the code seems fine from step by step testing with debugger.

Your problem is with the following line in the Afisare class:
Adaugare ad = new Adaugare();
You can't simply new one activity from another activity and expect to access a shared list between them. To share instance data between java objects you need a reference to the other object. Creating a new instance will create a new empty list. That's why you are "losing" data. A quick fix would be to make the list static so it can be accessed from any instance.
But since you're dealing with Android, the right way to share data between activities is by using intent extras. The first activity starts the second activity via an intent. The first activity places the desired data in the intent as extras. The second activity uses getIntent() and the various methods on Intent to access the extras.
One last tip, in Android, you never use the new operator with Activities. Activities are created by the system to service an intent. If you find yourself using the new operator, that's a sign that you're doing something wrong.

setText on button from another activity android

I have a problem, I want to click on the list, calling a new activity and rename the button to another name.
I tried several things, nothing worked, can someone please help me?
My class EditarTimes:
private AdapterView.OnItemClickListener selecionarTime = new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView arg0, View arg1, int pos, long id) {
t = times.get(pos);
CadastroTimes cad = new CadastroTimes();
CadastroTimes.salvar.setText("Alterar");
Intent intent = new Intent(EditarTimes.this, CadastroTimes.class);
startActivity(intent);
}
};
public class CadastroTimes extends AppCompatActivity {
private Time t;
private timeDatabase db;
private EditText edID;
private EditText edNome;
public Button salvar;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_cadastro_times);
edID = (EditText) findViewById(R.id.edID);
edNome = (EditText) findViewById(R.id.edNome);
db = new timeDatabase(getApplicationContext());
salvar = (Button) findViewById(R.id.btnCadastrar);
salvar.setText("Cadastrar");
String newString;
if (savedInstanceState == null) {
Bundle extras = getIntent().getExtras();
if(extras == null) {
newString= null;
} else {
newString= extras.getString("Alterar");
}
} else {
newString= (String) savedInstanceState.getSerializable("Alterar");
}
//button in CadastroTimes activity to have that String as text
System.out.println(newString + " AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");
salvar.setText(newString);
}
public void salvarTime(View v) {
t = new Time();
t.setNome(edNome.getText().toString());
if (salvar.getText().equals("Alterar")) {
db.atualizar(t);
exibirMensagem("Time atualizado com sucesso!");
} else {
db.salvar(t);
exibirMensagem("Time cadastrado com sucesso!");
}
Intent intent = new Intent(this, EditarTimes.class);
startActivity(intent);
}
private void limparDados() {
edID.setText("");
edNome.setText("");
edNome.requestFocus();
}
private void exibirMensagem(String msg) {
Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_LONG).show();
}
}
public class EditarTimes extends AppCompatActivity {
private Time t;
private List<Time> times;
private timeDatabase db;
private ListView lvTimes;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_editar_times);
lvTimes = (ListView) findViewById(R.id.lvTimes);
lvTimes.setOnItemClickListener(selecionarTime);
lvTimes.setOnItemLongClickListener(excluirTime);
times = new ArrayList<Time>();
db = new timeDatabase(getApplicationContext());
atualizarLista();
}
private void excluirTime(final int idTime) {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Excluir time?")
.setIcon(android.R.drawable.ic_dialog_alert)
.setMessage("Deseja excluir esse time?")
.setCancelable(false)
.setPositiveButton(getString(R.string.sim),
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
if (db.deletar(idTime)) {
atualizarLista();
exibirMensagem(getString(R.string.msgExclusao));
} else {
exibirMensagem(getString(R.string.msgFalhaExclusao));
}
}
})
.setNegativeButton(getString(R.string.nao),
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
builder.create();
builder.show();
atualizarLista();
}
private void atualizarLista() {
times = db.listAll();
if (times != null) {
if (times.size() > 0) {
TimeListAdapter tla = new TimeListAdapter(
getApplicationContext(), times);
lvTimes.setAdapter(tla);
}
}
}
private AdapterView.OnItemClickListener selecionarTime = new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> arg0, View arg1, int pos, long id) {
t = times.get(pos);
Intent intent = new Intent(EditarTimes.this, CadastroTimes.class);
String strName = "Alterar";
intent.putExtra("Alterar", strName);
startActivity(intent);
}
};
private AdapterView.OnItemLongClickListener excluirTime = new AdapterView.OnItemLongClickListener() {
public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
int pos, long arg3) {
excluirTime(times.get(pos).getId());
return true;
}
};
private void exibirMensagem(String msg) {
Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_LONG).show();
}
public void telaCadastrar(View view) {
Intent intent = new Intent(this, CadastroTimes.class);
startActivity(intent);
}
public void botaoSair(View view) {
Intent intent = new Intent(this, TelaInicial.class);
startActivity(intent);
}
}

You can pass the button caption to CadastroTimes with intent as
Intent intent = new Intent(EditarTimes.this, CadastroTimes.class);
intent.putExtra("buttontxt","Changed Text");
startActivity(intent);
Then in CadastroTimes.java set the text of the button to the new value that you passed. The code will look like:
button = (Button)findViewById(R.id.button); // This is your reference from the xml. button is my name, you might have your own id given already.
Bundle extras = getIntent().getExtras();
String value = ""; // You can do it in better and cleaner way
if (extras != null) {
value = extras.getString("buttontxt");
}
button.setText(value);
Do remember to do it in onCreate after setContentView

//From Activity
Intent intent = new Intent(EditarTimes.this, CadastroTimes.class);
intent.putExtra("change_tag", "text to change");
startActivity(intent);
//To Activity
public void onCreate(..){
Button changeButton = (Button)findViewById(R.id.your_button);
// Button to set received text
Intent intent = getIntent();
if(null != intent &&
!TextUtils.isEmpty(intent.getStringExtra("change_tag"))) {
String changeText = intent.getStringExtra("change_tag");
// Extracting sent text from intent
changeButton.setText(changeText);
// Setting received text on Button
}
}

1: Use intent.putExtra() to share a value from one activity another activity, as:
In ActivityOne.class :
startActivity(
Intent(
applicationContext,
ActivityTwo::class.java
).putExtra(
"key",
"value"
)
)
In ActivityTwo.class :
var value = ""
if (intent.hasExtra("key")
value = intent.getStringExtra("key")
2: Modify button text programatically as:
btn_object.text = value
Hope this will help you

For changing the button text:
Use a static method to call from the other activity to directly modify the button caption.
Use an intent functionality, which is preferable.
Use an Interface and implement it, which is used for communicating between activities or fragment in a manner of fire and forget principle.

Now, i got you:
Your EditarTimes activity with listview:
//set setOnItemClickListener
youtListView.setOnItemClickListener(new android.widget.AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view,int position, long id) {
Intent i = new Intent(EditarTimes.this, CadastroTimes.class);
//text which you want to display on the button to CadastroTimes activity
String strName = "hello button";
i.putExtra("STRING_I_NEED", strName);
}
});
In CadastroTimes activity,
under onCreate() method, get the text string as:-
String newString;
if (savedInstanceState == null) {
Bundle extras = getIntent().getExtras();
if(extras == null) {
newString= null;
} else {
newString= extras.getString("STRING_I_NEED");
}
} else {
newString= (String) savedInstanceState.getSerializable("STRING_I_NEED");
}
//button in CadastroTimes activity to have that String as text
yourButton.setText(newString);

Ok, so the first step would be to take the button you want and make it a public static object (and put it at the top of the class).
public static Button button;
Then you can manipulate that using this in another class:
ClassName.button.setText("My Button");
In your case it is
CadastroTimes.salvar.setText("Alterar");

if you want to change value from that do not do not go the activity via intent you can use file to save value to file or you have multiple values the use database and access
the value oncreate to set the value of text....

In my case, I had to send an EditText value from a Dialog styled Activity, which then got retrieved from a Service.. My Example is similar to some of the above answers, which are also viable.
TimerActivity.class
public void buttonClick_timerOK(View view) {
// Identify the (EditText) for reference:
EditText editText_timerValue;
editText_timerValue = (EditText) findViewById(R.id.et_timerValue);
// Required 'if' statement (to avoid NullPointerException):
if (editText_timerValue != null) {
// Continue with Button code..
// Convert value of the (EditText) to a (String)
String string_timerValue;
string_timerValue = editText_timerValue.getText().toString();
// Declare Intent for starting the Service
Intent intent = new Intent(this, TimerService.class);
// Add Intent-Extras as data from (EditText)
intent.putExtra("TIMER_VALUE", string_timerValue);
// Start Service
startService(intent);
// Close current Activity
finish();
} else {
Toast.makeText(TimerActivity.this, "Please enter a Value!", Toast.LENGTH_LONG).show();
}
}
And then inside my Service class, I retrieved the value, and use it inside onStartCommand.
TimerService.class
// Retrieve the user-data from (EditText) in TimerActivity
intent.getStringExtra("TIMER_VALUE"); // IS THIS NEEDED, SINCE ITS ASSIGNED TO A STRING BELOW TOO?
// Assign a String value to the (EditText) value you retrieved..
String timerValue;
timerValue = intent.getStringExtra("TIMER_VALUE");
// You can also convert the String to an int, if needed.
// Now you can reference "timerValue" for the value anywhere in the class you choose.
Hopefully my contribution helps!
Happy coding!

Accessing view reference of another Activity is a bad practice. Because there is no guarantee if the reference is still around by the time you access it (considering the null reference risk).
What you need to do is to make your other Activity read values (which you want to display) from a data source (e.g. persistence storage or shared preferences), and the other Activity manipulates these values. So it appears as if it changes the value of another activity, but in reality it takes values from a data source.

Using SharedPreferences:
Note: SharedPreferences saves data in the app if you close it but it will be lost when it has been deleted.
In EditarTimes.java:
private AdapterView.OnItemClickListener selecionarTime = new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView arg0, View arg1, int pos, long id) {
t = times.get(pos);
SharedPreferences.Editor editor = getSharedPreferences("DATA", MODE_PRIVATE).edit();
editor.putString("btnText", "Your desired text");
editor.apply();
Intent intent = new Intent(EditarTimes.this, CadastroTimes.class);
startActivity(intent);
}
};
In CadastroTimes.java
public Button salvar;
salvar.setText(getSharedPreferences("DATA", MODE_PRIVATE).getString("btnText", ""));
//note that default value should be blank

As far as my thoughts go, I can realize that the problem is not with the code you provided as it seems to be implemented correctly. It is possible that you have saved the activityState somewhere in your actual code and because it is not implemented properly, the savedInstanceState found in the onCreate method is not null but the required information is missing or not correct. That's why newString is getting null and salvar textview is getting blank.
Here, I need to know which one is more useful to you - information from getIntent() or from savedInstanceState? The code you provided insists me to assume that savedInstanceState has got the preference.
If you prefer savedInstanceState, then you may use SharedPreferences like this to get the same value you want:
private SharedPreferences mPrefs;
private String newString;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
........
// try to get the value of alterarValue from preference
mPrefs = getSharedPreferences("MyData", MODE_PRIVATE);
newString = mPrefs.getString("alterarValue", "");
if (newString.equals("")){
// we have not received the value
// move forward to get it from bundle
newString = getIntent().getStringExtra("Alterar");
}
// now show it in salvar
salvar.setText(newString);
}
protected void onPause() {
super.onPause();
// you may save activity state or other info in this way
SharedPreferences.Editor ed = mPrefs.edit();
ed.putString("alterarValue", newString);
ed.commit();
}
Or if you don't need to get it from savedInstanceState, please use it:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
........
// try to get the value of alterarValue from bundle
String newString = getIntent().getStringExtra("Alterar");
// now show it in salvar
salvar.setText(newString);
}
That's all I know. Hope it will help. If anything goes wrong, please let me know.

In Android Studio, cannot invoke Activity B from Activity A more than once

Further to my previous post, I now want to invoke a child activity from the main activity a number of times. In my real project (as opposed to the noddy test below), when the child activity is invoked, its header displays, "Enter first data set" then invites the user to enter some data. This data is actually stored in a common class rather than being returned to the main activity. Then the child needs to be called again with a new prompt "Enter second data set", and the same thing happens.
What I cannot work out is how to do this. If I include two calls to the child, every time, only the second call appears to happen, the prompt appearing in the child activity being "Enter second data set" every time. This startActivityForResult() method is I believe, designed to be used when you want to call an activity and wait for the result (which you do with an onActivityResult() do you not), but it does not wait.
How on earth do I do this? Sample code follows.
Thank you to anyone who can clearly explain where I'm going wrong and what the right code should be.
MainActivity code extract
#Override
public void onResume(){
super.onResume();
TextView maintop = (TextView)findViewById(R.id.maintop);
maintop.setText(Common.mess1);
}
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button mainbutton = (Button)findViewById(R.id.mainbutton);
mainbutton.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View view)
{
Intent intent1 = new Intent(MainActivity.this,Child.class);
intent1.putExtra("Prompt", "Enter first data set");
startActivityForResult(intent1,1);
onActivityResult(1,1,intent1);
}
});
mainbutton.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View view)
{
Intent intent2 = new Intent(MainActivity.this,Child.class);
intent2.putExtra("Prompt", "Enter second data set");
startActivityForResult(intent2,1);
onActivityResult(1,1,intent2);
}
});
}

You can only have one click listener in the button, so when you call set for the 2nd time it replaces the listener.
What you need to do is set the click listener for the enter first data, don't call to onActivityResult(1,1,intent1) that's not how you do it, you need override the method, and in onActivityResult call the 2nd.
Something like this:
static final int FIRST_INTENT = 1;
static final int SECOND_INTENT = 2;
#Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button mainbutton = (Button)findViewById(R.id.mainbutton);
mainbutton.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View view)
{
Intent intent1 = new Intent(MainActivity.this,Child.class);
intent1.putExtra("Prompt", "Enter first data set");
startActivityForResult(intent1,FIRST_INTENT);
}
});
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == FIRST_INTENT) {
if (resultCode == RESULT_OK) {
Intent intent2 = new Intent(MainActivity.this,Child.class);
intent2.putExtra("Prompt", "Enter second data set");
startActivityForResult(intent2,SECOND_INTENT);
}
}
}
And in your child activity
//DO SOMETHING
....
setResult(RESULT_OK)
finish();
}
For more check
[http://developer.android.com/intl/es/training/basics/intents/result.html]
[http://developer.android.com/intl/es/reference/android/app/Activity.html#setResult%28int%29]