Android ActionBar.Tab, Fragments, Sub-fragments

Question

I currently have an Android app which has a few tabs (3 to be exact) in a navigation area. Clicking on each tab shows the fragment associated with the tab.

I want to be able to click on a button in the fragment that is showing and display a new fragment, which isn't part of any of the tabs. Basically, it's like a sub-screen for the previous page.

I was able to get the "sub-fragment" to display, and clicking on the back button will take me to the previous fragment which is what I want.

My problem is that when I click on another tab, the "sub-fragment" isn't going away. And if I click the back button, I get an IllegalStateException saying Fragment1 has already been added.

Here is some of the code which hopefully will help answer my question.

MainActivity:

public void OnTabSelected(ActionBar.Tab tab, FragmentTransaction ft)
    {
        string tabTag = tab.Tag.ToString();

        Fragment f = FragmentManager.FindFragmentByTag(tabTag);

        if (f != null)
        {
            ft.Show(f);
        }
        else
        {
            switch (tabTag)
            {
                case "Tab1":
                    f = new Fragment1();
                    break;
                case "Tab2":
                    f = new Fragment2();
                    break;
                case "Tab3":
                    f = new Fragment3();
                    break;
                default:
                    f = new NotImplementedTabFragment();
                    break;
            }

            ft.Add(Resource.Id.fragmentContainer, f, tabTag);
         }
    }

    public void OnTabUnselected(ActionBar.Tab tab, FragmentTransaction ft)
    {
        string tabTag = tab.Tag.ToString();

        Fragment f = FragmentManager.FindFragmentByTag(tabTag);

        if (f != null)
        {
            ft.Hide(f);
        }
    }

Fragment1:

public class Fragment1 : Fragment
{

    public override Android.Views.View OnCreateView(Android.Views.LayoutInflater inflater, Android.Views.ViewGroup container, Bundle savedInstanceState)
    {
        base.OnCreateView(inflater, container, savedInstanceState);

        var view = inflater.Inflate(Resource.Layout.Fragment1, container, false);
        return view;
    }

    protected void OnButtonClick(object sender, Android.Widget.AdapterView.ItemClickEventArgs e)
    {
        var t = items[e.Position].ToString();
        FragmentTransaction fragmentTransaction = FragmentManager.BeginTransaction();
        fragmentTransaction.Replace(Resource.Id.fragmentContainer, new SubFragment());
        fragmentTransaction.AddToBackStack(null);
        fragmentTransaction.Commit();
    }
}

This is written in Xamarin (C#), but I do understand Java code, so any help/examples using Java are fine.

Update:

I realized that my MainActivityLayout.axml file was using a RelativeLayout instead of a FrameLayout this is why I had to use attach/detach instead of show/hide. Here is my new layout:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <FrameLayout
        android:id="@+id/fragmentContainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="1" />
</LinearLayout>

It still isn't working as expected, but I don't get the exception anymore saying the fragment has already been added.

Update 2:

I've decided to scrap trying to use the OnTabSelected and OnTabUnselected and just use delegates since I'm using C#. The important code is this:

private void AddTab(Tab tab, Fragment fragment)
{
    Android.App.ActionBar.Tab droidTab = this.ActionBar.NewTab();
    droidTab.SetCustomView(new TabLayout(this));
    droidTab.SetTag(tab.ToString());

    droidTab.TabSelected += delegate(object sender, ActionBar.TabEventArgs e)
    {
        e.FragmentTransaction.Replace(Resource.Id.fragmentContainer, fragment);
    };

    this.ActionBar.AddTab(droidTab);
}

Answer 1

I think what you need to do is save a reference to SubFragment

Fragment subFrag;
protected void OnButtonClick(object sender, Android.Widget.AdapterView.ItemClickEventArgs e)
{
    var t = items[e.Position].ToString();
    FragmentTransaction fragmentTransaction = FragmentManager.BeginTransaction();
    subFrag =  new SubFragment();
    fragmentTransaction.Replace(Resource.Id.fragmentContainer, subFrag);
    fragmentTransaction.AddToBackStack(null);
    fragmentTransaction.Commit();
}

Then when Fragment1 is detatched, remove the subFrag

@Override public void onDetach() {
    if (subFrag != null) {
         FragmentTransaction fragmentTransaction = FragmentManager.BeginTransaction();
         fragmentTransaction.Remove(subFrag );
         fragmentTransaction.Commit();
    }
    super.onDetach();
}

Another (though a bit crude in my opinion) option could be to implement a getSubFragment() method in Fragment1 and do:

public void OnTabUnselected(ActionBar.Tab tab, FragmentTransaction ft)
{
    string tabTag = tab.Tag.ToString();

    Fragment f = FragmentManager.FindFragmentByTag(tabTag);

    if (f instanceof Fragment1) {
        Fragment subFrag = ((Fragment1)f).getSubFragment();
        if (subFrag != null) {
            ft.Remove(f); 
        }
    }
    if (f != null)
    {
        ft.Hide(f);
    }
}