Question

The Problem

Before I describe my current setup I will describe my problem. I need to have hierarchal navigation between fragments inside separate tabs. Say I drill down on level in a tab, I then switch tabs and then go back to the first, original tab, I need it to be on the drilled down level and then have the ability to go back up to the top level of that tab.

Now onto my setup.

I have an application with one activity called MainActivity. This activity is what controls my tabbed action bar. I have followed many different tutorials to handle the switching of Fragments when a tab is selected and here is the code below that works drawing your attention to the onTabSelected and onTabUnselected methods.

MainActivity — Tab Listener

public static class MyTabListener<T extends Fragment> implements ActionBar.TabListener {
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;
    private final Bundle mArgs;
    private Fragment mFragment;

    public MyTabListener(Activity activity, String tag, Class<T> clz) {
        this(activity, tag, clz, null);
    }

    public MyTabListener(Activity activity, String tag, Class<T> clz, Bundle args) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
        mArgs = args;

        // Check to see if we already have a fragment for this tab, probably
        // from a previously saved state.  If so, deactivate it, because our
        // initial state is that a tab isn't shown.
        mFragment = mActivity.getFragmentManager().findFragmentByTag(mTag);
        if (mFragment != null && !mFragment.isDetached()) {
            FragmentTransaction ft = mActivity.getFragmentManager().beginTransaction();
            ft.detach(mFragment);
            ft.commit();
        }
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        Log.e("FRAGMENT","Selected Fragment With Tag " + mTag);
        if (mFragment == null) {
            mFragment = Fragment.instantiate(mActivity, mClass.getName(), mArgs);
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            ft.attach(mFragment);
        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            ft.detach(mFragment);
        }
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        Toast.makeText(mActivity, "Reselected!", Toast.LENGTH_SHORT).show();
    }


}

When I am on Tab1 viewing Fragment1', when a button is pressed I then show anotherFragmentcalledFragment2` which I need the ability to go back from. The code below works if I just stay on that tab however when navigating away from the tab and back to it, everything messes up.

MainActivity — Showing second fragment

Fragment tdFrag = Fragment.instantiate(this, SecondFragment.class.getName());
    FragmentTransaction ft = getFragmentManager().beginTransaction();
    ft.replace(android.R.id.content, tdFrag, "secondfrag");
    ft.addToBackStack(null);
    ft.commit();

My Thoughts

I think it must be the way I detach the fragments and handle the switching over when a new tab is pressed. Maybe I need to implement some way of storing each individual backstack for each tab and loading the fragments from that instead of the system back stack?

Any help would be great. I have tried to explain it as thoroughly and simply as possible.

Thanks in advance.

Answer 1

Ok so after a bit of experimentation I decided to implement a custom backstack using enumerated types.

I have two types of enumerated types: a ViewType and CurrentTab type. The CurrentTab type tells me what tab I’m currently viewing and the ViewType tells me what view is being viewed in these tabs. I have an instance of a ViewType for each tab I have to store where I am in the hieerarchy.

To implement a backstack I override the method thats called when the back button is pressed.

public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK) {

             return true;
        }
     return super.onKeyDone(keyCode,event);
}

So in where it checks for the back button I put my code to check the current tab and the separate view types. That way I know where I am and if I push back I know where I need to go.

I hope this helps any questions just post a comment.