My original answer suggested using add instead of replace for the Fragment transaction. I have since learned that either can be used in this case. For more info on the differences, see this, this and this
Since my add/replace idea was off base, I've changed my answer to a simple Fragment tutorial. One Fragment inflated from one Activity. I've included the code for Fragment to Activity communication (the reason for the OPs problem) but left comments on what could be deleted if that's not needed. The only thing done in the Activity is launching the Fragment then receiving a message back from that Fragment. The Fragment has a button that will cause a message to be sent back to the Activity. The message will then be Logged.
In both classes, if no communications is needed from the Fragment to the Activity, delete anything that is marked TODO:
// this is what controls whether you use a Fragment from the support library
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
public class SimpleActivity extends AppCompatActivity
// TODO: delete "implements SimpleFragment.OnFragmentInteractionListener" from this
// line (leave the '{')
implements SimpleFragment.OnFragmentInteractionListener {
private static final String TAG = SimpleActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
SimpleFragment fragment = new SimpleFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.add(R.id.fragment_container, fragment)
.commit();
}
// TODO: this entire method can be deleted
@Override
public void onFragmentInteraction(String message) {
// This is where you can act on the message from the Fragment. You would do
// things that are done from an Activity or you may pass the message on
// to another Fragment.
Log.d(TAG, message);
}
}
Most import statements aren't shown, I left this one in to indicate using the support library
import android.support.v4.app.Fragment;
public class SimpleFragment extends Fragment {
private OnFragmentInteractionListener mListener; // TODO: delete this line
public SimpleFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_simple, container, false);
Button button = (Button)rootView.findViewById(R.id.msg_button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// TODO: delete these 3 lines, do something else with the button click
if (mListener != null) {
mListener.onFragmentInteraction("Message from Fragment");
}
}
});
return rootView;
}
// TODO: this entire method can be deleted
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
// TODO: this entire method can be deleted
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
// TODO: this entire method can be deleted
public interface OnFragmentInteractionListener {
void onFragmentInteraction(String message);
}
}
Now the layout files. 1st activity_simple.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/fragment_container"
>
</FrameLayout>
</android.support.constraint.ConstraintLayout>
Then fragment_simple.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Info to Activity"
android:id="@+id/msg_button"
/>
</RelativeLayout>
This is a very basic sample. Here is a more extensive guide for Fragment usage.
