Calling a new layout from a class

Question

I was wondering if it's possible to use setContentView on a class? I'm planning to call a new layout once the class is called. So basically, I'm trying to change the view once I detect an nfc tag.

Main_Activity

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main__screen);
    readCard = new ReadCard(this);
    enableReaderMode();
}

public void enableReaderMode()
{
    Activity activity = this;
    NfcAdapter nfc = NfcAdapter.getDefaultAdapter(activity);
    if (nfc != null)
    {
        nfc.enableReaderMode(activity, readCard, READER_FLAGS, null);
    }

}

Class

private Main_Screen mainScreen;
private Context context;
public String PINHolder = null;

IsoDep isoDep;
Activity Main_Screen = (Activity) context;
public ReadCard(Main_Screen mainScreen)
{
    this.mainScreen = mainScreen;
}
@Override
public void onTagDiscovered(Tag tag)
{


    isoDep = IsoDep.get(tag);

    if (isoDep != null)
    {
        beepSound.start();
        try
        {
            isoDep.connect();
            mainScreen.setContentView(R.layout.pin_login);
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }
}

An activity is a type of class... you can call it in an activity. Or just recall it once the class is called with an intent for the activity to update it's view — SQLiteNoob, Jun 09 '16 at 02:16
You want to change the View after you instantiated an object? Is that it? — Mauker, Jun 09 '16 at 02:20
@SQLiteNoob - I'm try to call a method from a class to change the layout view. Mauker - somehow yes. I'm trying to call it from a different class' method. — Jujumancer, Jun 09 '16 at 02:23
I'm not quite sure I follow. Why can't you just call `setContentView` again? — Mauker, Jun 09 '16 at 02:25
if you're just calling another class without changing the activity, Mauker is right — SQLiteNoob, Jun 09 '16 at 02:26
That's what I am trying to do now. Unfortunately it is not changing. I get the error "only the original thread that created a view hierarchy can touch its views" — Jujumancer, Jun 09 '16 at 02:30
I guess the right term would be opening a new layout using a class instead of a button perhaps? — Jujumancer, Jun 09 '16 at 02:47

score 2 · Accepted Answer · edited May 23 '17 at 10:34

You can't do what you want that way, because only the Activity is "authorized" to modify its contents and children Views. You also can't touch the UI Thread from a background one.

There are some ways you can achieve what you want, I'll try to list some:

You could "send a message" to the Activity once your class did what it was supposed to do. You can do that by using the LocalBroadcastManager (as seem on this question), or Greenrobot's EventBus;
You could try to use some sort of listener;
Use Handlers.

For more info on how you can communicate with the UI thread (in this case, with your Activity), check the Android training guide.

Alright. Thank you very much. At least I got a clarification that what I am doing will not work. Thank you very much! — Jujumancer, Jun 09 '16 at 02:59

Calling a new layout from a class

1 Answers1