How can I show a new Fragment within a single tab?

Question

I am creating a three tabs that contains one fragment each now I want to replace the first Tab's Fragment with a new Fragment within the same Tab. How can I do that with the tab remaining the same?

My Code -

Tab_Widget.java

    public class Tab_Widget extends TabActivity {

            TabHost tabHost; 

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.tab_host);

            tabHost = getTabHost();

            tabHost.addTab(tabHost.newTabSpec("Tab1")
                .setIndicator("Tab1")
                .setContent(new Intent().setClass(this, main_activity.class)));

            tabHost.addTab(tabHost.newTabSpec("Tab2")
                .setIndicator("Tab2")
                .setContent(new Intent().setClass(this, second_activity.class)));

            tabHost.addTab(tabHost.newTabSpec("Tab3")
                    .setIndicator("Tab3")
                    .setContent(new Intent().setClass(this, third_activity.class)));

            tabHost.setCurrentTab(0);
        }
     }

---

main_activity.java

public class main_activity extends FragmentActivity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.mainfragment);
    }
}

---

main_fragment.java

public class main_fragment extends Fragment
{
    LinearLayout mLayout;
    Button mButton;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        mLayout = (LinearLayout) inflater.inflate(R.layout.main_view, null);
        mButton = (Button) mLayout.findViewById(R.id.btn);
        mButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {

                Fragment mFragment = new third_fragment_view();
                FragmentTransaction ft = getFragmentManager().beginTransaction();
//              ft.replace(R.id.Maincontainer, mFragment);
                ft.replace(R.id.main_fragment, mFragment);
                ft.addToBackStack(null);
                ft.commit();
            }
        });
        return mLayout;
    }
}

---

My XML

mainfragment.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/Maincontainer"
android:layout_width="match_parent"
android:layout_height="match_parent">

<fragment
  android:name="com.fragment.main_fragment"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:id="@+id/main_fragment">
</fragment>
</LinearLayout>

By, this the Fragment is getting called no doubt, but its overlapping the previous Fragment.

Answer 1

You have a structure like so:

TabActivity
 -> Tab1 = FragmentActivity = MainFragment
 -> Tab2          
 -> Tab3          

From inside of MainFragment you are trying to replace the contents of its container (itself).

It would be best if the MainFragment called a customised TabActivity which in turn called a replace on it's container, either like so (Which may likely fall foul of the same problem as it's basically running the same code from the same place, but it should give you a basic idea of what I'm suggesting):

    Fragment newFragment = new FragmentToChangeTo();
    CustomTabActivity tabActivity = (CustomTabActivity) getActivity();
    tabActivity.changeFragment(newFragment);

If this doesn't work try doing a similar thing but instead of calling the activity directly pass commands to it through Intents & Actions (or Bundles) containing information on what to change which container to.

I would have preferred to say /why/ Fragments don't work well with Fragment-in-fragment and related intricacies: check here to see why I suggest cutting fragments out of the control of fragments.