How to set a button visible from another activity in android

Question

I have a very simple problem. I have a invisible button in my Main Activity, and I have a second Activity that makes that button visible. In the second activity I don´t have a p

Answer 1

You should set up a communication between the 2 activities. You can achieve this with startActivityForResult() and onActivityResult()

MainActivity:

public class MainActivity extends Activity {

    public static final int REQUEST_CODE_SECOND_ACTIVITY = 100; // This value can be any number. It doesn't matter at all. The only important thing is to have the same value you started the child activity with when you're checking the onActivityResult.
    public static final String SHOW_BUTTON = "shouldShowButton";

    private Button mMyButtonToBeHidden;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mMyButtonToBeHidden = (Button) findViewById(R.id.buttonToBeHidden);

        findViewById(R.id.openSecondActivity).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivityForResult(new Intent(MainActivity.this, SecondActivity.class), REQUEST_CODE_SECOND_ACTIVITY);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == REQUEST_CODE_SECOND_ACTIVITY && resultCode == RESULT_OK) {
            //Check if you passed 'true' from the other activity to show the button, and also, only set visibility to VISIBLE if the view is not yet VISIBLE
            if (data.hasExtra(SHOW_BUTTON) && data.getBooleanExtra(SHOW_BUTTON, false) && mMyButtonToBeHidden.getVisibility() != View.VISIBLE) {
                mMyButtonToBeHidden.setVisibility(View.VISIBLE);
            }
        }
    }
}

SecondActivity:

public class SecondActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        findViewById(R.id.hide_main_activity_button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.putExtra(MainActivity.SHOW_BUTTON, true);
                setResult(RESULT_OK, intent);
                finish();
            }
        });
    }
}