class life cycle with ActionBar Sherlock Tab fragments

Question

I'm working on one of my first Android applications and got stuck with the understanding of how controllers/classes lifecycle are arranged. I'm coming from an iOS background.

Basicly what I did was following this simple tutorial

So from what I understand I bind a TabListener to the Fragment. When switching tabs the TabListener's onTabSelected() gets called and each time a new instance of FragmentA/Fragment B is created.

That leads to the fact that every time I switch tabs all onCreate..() methods are called again.

I don't want to create a new fragment instance every time I switch tabs but rather use the one which was created intially at application start.

The question is how can I switch tabs without killing the fragments in there?

Answer 1

You can achieve this by just attaching/detaching the fragments, on your tab listener every time a tab is unselected detach the current fragment and on your onTabSelected method check if you have created the fragment before.

private Fragment       mFragment;
private final String   mTag;
private final Class<T> mClass;

public TabListener(String pTag, Class<T> pClass) {
    mTag = pTag;
    mClass = pClass;
}

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
    if ( mFragment == null ) {
        try {
            mFragment = (Fragment)mClass.newInstance();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        ft.add(R.id.fragment_container,mFragment,mTag);
    } else {
        ft.attach(mFragment);
    }   
}

@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {

    if ( mFragment != null ) {
        ft.detach(mFragment);
    }
}

   public void onTabReselected(Tab tab, FragmentTransaction ft) {
    //Nothing   
   }

Then you can instantiate your listener as in

TabListener l = new TabListener<MyFragment>(tabTag, MyFragment.class)