Sending variable between activities

Question

This question is simple. There are for example 2 activities Main Activity and Main Activity 2. How can I send string(for example) from Main Activity to Main Activity 2. Let's say if Main Activity 2 gets string. It calls a function to change that string. And then how to send that changed string back to Main Activity?

You return it as part of the result intent – Gabe Sechan Apr 21 '16 at 21:00 — Gabe Sechan, Apr 21 '16 at 21:00

score 0 · Answer 1 · answered Apr 21 '16 at 21:38

The Standard Way:

If you want to send a primitive data from Activity1 to Activity2, you need to use Intent. For example if you just want to send a String:

public class Activity1 extends Activity {
   public static final String EXTRA_STRING = "extra_string";

   private void sendString(String s) {
        Intent intent = new Intent(this, Activity2.class);
        intent.putExtra(EXTRA_STRING, s);
        startActivity(intent);
   }
}

Suppose you change that string in Activity2 and also want the result back to Activity1, you need to use startActivityForResult() in Activity1 and setResult() in Activty2.

For example:

public class Activity1 extends Activity {
   public static final String EXTRA_STRING = "extra_string";
   private static final int REQUEST_CODE = 1;

   @Override
   protected void onActivityResult(int requestCode, int resultCode, Intent data) {    
       if (requestCode == REQUEST_CODE && resultCode == RESULT_OK) {
           // Get the string back
           String changedString = data.getStringExtra(Activity2.EXTRA_STRING);
       }
   }


   private void sendString(String s) {
        Intent intent = new Intent(this, Activity2.class);
        intent.putExtra(EXTRA_STRING, s);
        startActivityForResult(intent, REQUEST_CODE);
   }
}

In Activity2:

public class Activity2 extends Activity {
    public static final String EXTRA_STRING = "string_extra";
    private String myString;

    @Override
    public void onCreate(Bundle bundle) {
         // receive the string from activity1
         if (getIntent() != null) {
              myString = getIntent().getStringExtra(Activity1.EXTRA_STRING);
         }  
    }

    // Send the string back to activity1
    private void sendBack() {
        Intent data = new Intent();
        data.putExtra(EXTRA_STRING, myString);
        setResult(RESULT_OK, data);
        finish();
    }
}

The downside of the method is you can only send primitive variable. If you want to send an object, it must implements Parcelable or Serializable.

The Quick and Easy Way:

You can send variable of any kind, any complicated object between activity, service or whatever you want using EventBus. Please take a look at the Documentation to know how to use it. It's really quick and easy.

score 0 · Accepted Answer · answered Apr 21 '16 at 21:39

0

From Main activity 1 send the string:

                Intent intent = new Intent(this, MainActivity2);
                intent.putExtra("string", stringVal);
                intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                startActivity(intent);

Then in Main Activity 2, receive the string:

String str = getIntent().getExtras().getString("string");

Then just change the value and send it back to Main Activity 1, you could get the intent within the onResume if you want, but check for nulls.

answered Apr 21 '16 at 21:39

Ushal Naidoo

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So when Main Activity 2 receive the string and make some changes to it. I can send it back to Main Activity activity by using similar code that you wrote above, just changing MainActivity2 to MainActivty and to change value of putExtra()? – Apr 21 '16 at 22:05
Correct, give it a try – Ushal Naidoo Apr 21 '16 at 22:06
This works, but it's not quiet what I'm looking for. I was not being specific enough in question and sorry for that. Actually what I want is to stay on layout page of Main Activity than to send string to Main activity 2 without Main Activity 2 and it's layout pop up on my device. Long story short, Main Activity 2 receives string and device always stays on Main Activity layout. Main Activity 2 changes string(let's say just replace 2 letters) and it sends string back to Main Activity where I can actually see changes(in Text View for example). – Apr 21 '16 at 23:00
Do you need an activity for that? Why not use a service or a class? What's the use case of using an activity? In that case you could possibly just have a public method that inputs a string and returns a string. But I don't know if that's good practive – Ushal Naidoo Apr 22 '16 at 01:20

Sending variable between activities

2 Answers2