This is not the best approach.
If you have an operation (function) that is executed periodically and whose result you want to get in more than one place of your application, do not do it in an Activity.
An Activity should not depend on another to perform its function.
Android provides the class Service for cases of this type.
In a Service the operations are executed independently of the other components of the application, however, communication between them is possible.
In this case, a possible approach is to use a Bound Service linked) :
(...) A linked service allows components (such as activities) to be linked to the service, send requests, receive responses, and even establish interprocess communication (IPC). , Linked Services )
Example that uses a service to calculate the square root.
SqrCalculatorService.java
public class SqrCalculatorService extends Service {
public static final int SQR_MSG = 0;
public static final String SQR_RESULT = "sqrResult";
public SqrCalculatorService() {
}
public static Intent makeIntent(Context context){
return new Intent(context, SqrCalculatorService.class);
}
private final Messenger mCalculateMessenger = new Messenger(new CalculateHandler());
private static class CalculateHandler extends Handler{
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case SQR_MSG:
double sqr = calculate(msg.arg1);
replyToCaller(msg.replyTo, sqr);
break;
default:
super.handleMessage(msg);
}
}
private static double calculate(int arg1) {
return Math.sqrt(arg1);
}
private static void replyToCaller(Messenger msg, double sqr) {
Message reply = Message.obtain(null, SQR_MSG);
Bundle data = new Bundle();
data.putDouble(SQR_RESULT, sqr);
reply.setData(data);
try {
msg.send(reply);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
@Override
public IBinder onBind(Intent intent) {
return mCalculateMessenger.getBinder();
}
}
MainActivity.java
public class MainActivity extends AppCompatActivity {
private Messenger mServiceMessenger = null;
private TextView tvResultado;
private EditText edValor;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tvResultado = (TextView) findViewById(R.id.tvResultado);
edValor = (EditText)findViewById(R.id.edValor);
}
@Override
protected void onStart() {
super.onStart();
if(mServiceMessenger == null){
bindService(SqrCalculatorService.makeIntent(this),
srvConnection, Context.BIND_AUTO_CREATE);
}
}
@Override
protected void onStop() {
unbindService(srvConnection);
super.onStop();
}
private ServiceConnection srvConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
mServiceMessenger = new Messenger(iBinder);
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
mServiceMessenger = null;
}
};
final Messenger mResultMessenger = new Messenger(new ResultHandler());
private class ResultHandler extends Handler {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case SqrCalculatorService.SQR_MSG:
Bundle data = msg.getData();
displaySQRResult(data);
break;
default:
super.handleMessage(msg);
}
}
private void displaySQRResult(Bundle data) {
double sqr = data.getDouble(SqrCalculatorService.SQR_RESULT);
tvResultado.setText(Double.toString(sqr));
}
}
public void onButtonClick(View v){
int value = Integer.parseInt(edValor.getText().toString());
Message msg = Message.obtain(null, SqrCalculatorService.SQR_MSG, value, 0);
msg.replyTo = mResultMessenger;
try {
mServiceMessenger.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin">
<TextView
android:id="@+id/lbValor"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Valor a calcular: "/>
<EditText
android:id="@+id/edValor"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_toEndOf="@+id/lbValor"
android:layout_toRightOf="@+id/lbValor"
android:layout_alignBaseline="@+id/lbValor"/>
<TextView
android:id="@+id/lbResultado"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/lbValor"
android:text="Resultado: "
android:layout_marginTop="24dp"/>
<TextView
android:id="@+id/tvResultado"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_toEndOf="@+id/lbResultado"
android:layout_toRightOf="@+id/lbResultado"
android:layout_alignBaseline="@+id/lbResultado"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/lbResultado"
android:layout_centerHorizontal="true"
android:layout_marginTop="24dp"
android:text="Calcular raiz quadrada"
android:onClick="onButtonClick"/>
</RelativeLayout>
Service registration in AndroidManifest.xml
<application>
....
....
<service
android:name=".SqrCalculatorService"
android:enabled="true"
android:exported="true">
</service>
</application>
