Do not get the rootLayoutContainer in a Fragment (Android 3.0 Preview)

I'm currently getting into the fragment API of the Android 3.0 Preview and have built the following minimal coding:

I have an Activty, which shall embed Fragment(s), which is currently implemented like this:

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

public static class InfoFragment extend开发者_开发技巧s Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // Inflate the layout for this fragment

        ViewGroup infoFragmentRoot = (ViewGroup) getActivity().findViewById(
                R.id.infoFragmentRoot) ;

        return inflater.inflate(R.id.infoFragment, container, false);
    }
}

}

The corresponding layout of the activity:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<fragment android:name="test.android.ui.cockpit.Cockpit$InfoFragment"
        android:id="@+id/infoFragment"
        android:layout_weight="1"
        android:layout_width="10dp"
        android:layout_height="match_parent" >
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" 
                 android:layout_height="match_parent" android:padding="12dp" android:id="@+id/infoFragmentRoot" >
        <TextView  
            android:layout_width="fill_parent" 
            android:layout_height="wrap_content" 
            android:text="@string/hello"
        />
    </LinearLayout>
</fragment>

Now, I do not understand why the ViewGroup container in the onCreateView() in the internal class InfoFragment is a nullpointer, nor do I understand, why

ViewGroup infoFragmentRoot = (ViewGroup) getActivity().findViewById(
                R.id.infoFragmentRoot) ;

returns also null.

Thanks for feedback.

---

You've got a few problems here. First of all, you don't want to be adding tags inside of the <fragment> tag. Think of the fragment tag as a placeholder. The fragment's onCreateView() method is responsible for defining the view hierarchy of your fragment, not the activity's layout XML file. What you can do though is create a separate layout XML file to be just the fragment's layout. Then inside of onCreateView(), you take the inflater passed in, and do something like this:

    View v = inflater.inflate(R.layout.frag1, container, false);
    TextView text1 = (TextView) v.findViewById(R.id.text1);
    text1.setText( myTextData );
    return v;

Notice that the attach parameter to inflate() is false? Android will take care of attaching the returned view to your container later.

Your activity's view hierarchy is not guaranteed to be in existence until the fragment gets the onActivityCreated() callback. So the attempt to get infoFragmentRoot could return null inside of onCreateView(). But I'm not even sure what is going on when that tag is buried inside of your <fragment>.

In this particular case, where you've embedded the tag in your activity's layout, the onInflate() callback of your fragment will be called with the rest of the attributes from your tag. The theory is that you could add those attributes to the arguments bundle on your fragment, then retrieve those values later in onCreateView() (using setArguments() and getArguments()). I say in theory because it appears there's a bug in the code that handles a configuration change (e.g., landscape to portrait), resulting in onInflate() being called after onCreateView() when the fragment is being reconstructed after a configuration change. See defect report http://code.google.com/p/android/issues/detail?id=14796.

For now, I recommend you extract your fragment's layout to a separate layout XML file (e.g., frag1.xml), the use my code above to inflate that layout in onCreateView(). And don't worry about any attributes being passed to onInflate().

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You also do not want to use onCreate to instantiate your layout, that all will be handled within the parent activity. Saving the bundle is about all ive done there so far