将我的应用程序转换为片段：如何处理活动？

Question

I'm planning to convert an existing android application to fragments layout.

The idea is to have the classical two panel layout (item list on left, and details on right).

Actually the application is composed by 4 activites:

1. A ChoiceListActivity with all the available options
2. 3 different activities, one for each operation available on the tool.

Now i started to work on the conversion and i created a FragmentActivity classs, that is the main class:

    public class MainFragment extends FragmentActivity {

    private static final String TAG = "MainFragment";

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_main);
        if(findViewById(R.id.fragment_container)!=null){
            Log.i(TAG, "No Tablet");
            Intent i = new Intent(MainFragment.this, main.ChoiceActivity.class);
            startActivity(i);
        } else {
            Log.i(TAG, "Tablet");
        }
    }
}

And i created a ChoiceListFragment: `

public class ChoiceListFragment extends ListFragment {

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        Toast.makeText(getActivity(), getListView().getItemAtPosition(position).toString(), Toast.LENGTH_LONG).show();
        super.onListItemClick(l, v, position, id);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);     
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        String[] options = getResources().getStringArray(R.array.listitems);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(inflater.getContext(), R.layout.list_item, options);
        setListAdapter(adapter);
        return super.onCreateView(inflater, container, savedInstanceState);
    }

}

That fragment will be the left side of the panel.

My problem is for the right side. The idea is that for every element of the list the corresponding activity (or fragment?) will be shown.

So what is the correct way?

1. Is a good idea to start an activity in the right fragment when the user select an item?

2. Or i must switch between fragments programmatically? And how to do that (i found many tutorials, but they use always the same activity for the right panel changing some data inside it)?

I have created the following class for the right fragment (but i'm not sure that i'm doing it correctly):

public class RightFragment extends Fragment {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {        
        return inflater.inflate(R.layout.main, container, false);
    }


}

I noticed that i can eventually change the layout using the LayoutInflater object during onCreate method, but this simply siwtch the layout on the screen, The objects declared in the layout aren't initialized (nor eventListener added, etc). So how to do that?

Maybe i should Create an Intent and use startActivity to launch the existing activities, or this is a bad idea into a fragment?

Actually the xml layout is:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >

    <fragment
        android:id="@+id/choicelist_fragment"
        android:name="main.fragments.ChoiceListFragment"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1" />

    <fragment
        android:id="@+id/right_fragment"
        android:name="main.fragments.RightFragment"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="2" />

</LinearLayout> 

Answer 1

Ok i found myself the solution, it was not clear on a first moment, but reading some documentation, looking at many tutorials maybe i understand how it works.

First of all i removed the second fragment *right_fragment* from the layout (check the question), i replaced it with an empty FrameLayout called *activity_container* that will be the container of my fragments.

The idea behind is simply use the FragmentManager to replace the fragment inside the container.

So i updated the onListItemClick method into the ChoiceListFragment, and depending on what is the list item tapped, it creates a new Fragment and replace it into the *activity_container*. The updated method is similar to the following:

public void onListItemClick(ListView l, View v, int position, long id) {            
        String itemName = getListView().getItemAtPosition(position).toString();
        switch(position){
        case OPTION_ONE:                getFragmentManager().beginTransaction().replace(R.id.activity_container, new OptionOneFragment()).commit();
            break;
        case RESISTOR_VALUE:
            getFragmentManager().beginTransaction().replace(R.id.activity_container, new OptionTwoFragment()).commit();
            break;
        default:
            Toast.makeText(getActivity(), getListView().getItemAtPosition(position).toString(), Toast.LENGTH_LONG).show();
            break;
        }       
        super.onListItemClick(l, v, position, id);
    }

In that way every component of the application has its own fragment, handled by a different class.

Answer 2

You're on the right track. On small screens, clicking a list item starts a DetailActivity, which is a simple wrapper around a DetailFragment. On a larger screen, clicking the list item would replace the right hand side with a new instance of DetailFragment.

If you are using eclipse and ADT, I would suggest taking a look at the MasterDetailFlow template, which can be accessed by creating a new Android project or a new Android Activity.