Can I update data members in one Activity from another Activity in the application?

Question

I've tried this and it works, but I didn't know if this was a bad thing or not, as all the help on data transfers between Activities seems to use intents.

In MainActivity I have:

static PilotRecord pilotRecord = new PilotRecord(); //PilotRecord just contains data item declarations

In MainActivity.onCreate:

pilotRecord.fuel = 100;

In MainActivity.onClick:

Intent intent = new Intent(this, SubActivity.class);
startActivityForResult(intent, 0);

In SubActivity.onCreate I have:

MainActivity.pilotRecord.fuel = 200;

In SubActivity.onClick:

MainActivity.pilotRecord.fuel = 300;
setResult(RESULT_OK);
finish();

When I start MainActivity, the fuel value is 100

If I click in MainActivity, SubActivity is displayed, as expected

If I click in SubActivity, MainActivity is displayed and the fuel value is now 300

If I press the Back button, MainActivity is displayed and the fuel value is now 200

Does anyone know of any potential issues with this as it seems simpler to me than setting up intents etc.

• Frink

Answer 1

Why don't you put the result in the result intent ?

Answer 2

It is my understanding that what you are doing will result in data loss.

The SubActivity should not be manipulating the data of the activity that called it. I don't think that there is any guarantee that your MainActivity even exists...

The system may decide to kill it at any time and restart it when your SubActivity signals that it is ready to return to the MainActivity.

You should pass back the data in a bundle and let MainActivity modify its data based on the results.

    Bundle stats = new Bundle();
    stats.putString("fuel","300"); 
    setResult(RESULT_OK, "PilotRecord", stats);
    finish();

Also, remember that you should be saving the "Fuel" level to some sort of persistent storage when onPause() is called in your MainActivity.

I would suggest reading the documentation for Activity carefully since it is quite important to implement the correct callbacks.

Answer 3

If you really want to hack it, create another class that hold all your static variables that needs to be shared.