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Android - Basic Steps (Fragments)

Fragments

  • This functionality allows to support multiple UI panes / User behavior at the same time
  • A fragment is part of an Activity
  • Multiple Fragments can be embedded in an activity to create  a Multi-Pane UI
  • A single fragment can be reused across multiple activities+

Fragment Lyfeclycle States

  • Resumed
    • Is visible in the sunning state
  • Paused
    • Another activity is in the foreground and has focus, containing activity is visible
  • Stopped
    • Fragment is not visible

Fragment Lyfeclycle Methods 

  • onAttach()
    • Fragment is created and attached to the activity
  • onCreate()
    • Initialize the fragment
  • onCreateView
    • Fragments set up &returns its user inferface
  • onActivityCreated
    • activity has completed the onCreate() method and the fragment has been installed
  • onStart()
    • when activity become visible
  • onResume
    • Become visible and ready for user interaction
  • onPause
    • activity is visible without the focus
  • onStop
    • activity is no longer visible
  • onDestroyView
    • the view created in onCreate() method has been detached from the activity 
    • Clean up view resources
  • onDestroy
    • Fragment is no longer in use
    • Clean up fragment resources
  • onDetach
    • null out references to hosting activities

Add a Fragment Statically

  • A fragment layout can be inflated/implemented in OnCreateView
  • OnCreateView return the View at the root of the Fragments's layout, where R.layout.quote_fragment is the fragment's layout 
          return inflater.inflate(R.layout.quote_fragment, container, false);
  • This View is added to the containing activity

Insert two Fragments (Menu -Details)

  • In the activity_main.xml file (the one that is launched) change a Linear Layout
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:baselineAligned="false"
    android:orientation="horizontal" 
> 
</LinearLayout>
  • Inside add the Fragments
The first fragment is for the menu       
       <fragment
        android:id="@+id/titles"
        android:layout_width="0px"
        android:layout_height="match_parent"
        android:layout_weight="1"
        class="com.example.myfragmentstatic.Menu" />

The second fragment is for the details

        <fragment
        android:id="@+id/details"
        android:layout_width="0px"
        android:layout_height="match_parent"
        android:layout_weight="2"
        class="com.example.myfragmentstatic.Details" />


  • In the Menu.java
    • Extends from ListFragment
    • Override the mehod onActivityCreated to load the List

@Override
public void onActivityCreated(Bundle savedState) {
super.onActivityCreated(savedState);

getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
setListAdapter(new ArrayAdapter<String>(getActivity(),
R.layout.title_item, getResources().getStringArray(R.array.Titles) ));
}


R.layout.title_item - Is an XML file named title_item with a TextView as content


<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="?android:attr/activatedBackgroundIndicator"
    android:orientation="vertical"
    android:padding="5dip"
    android:textSize="32sp" >

</TextView>



R.array.Titles - Is an array with the menu options defined in the strings.xml file

<string-array name="Titles">
        <item>The Tragedy of Hamlet, Prince of Denmark</item>
        <item>King Lear</item>
        <item>Julius Caesar</item>
    </string-array>

  • Add functionality to show the detail according with the menu option selected
    • Define an Interface
        public interface ListSelectionListener {
public void onListSelection(int index);
}
    • Create a global variable of type ListSelectionListener 
             private ListSelectionListener mListener = null;

    • Override the method onAttach
In this case is getting the father activity and using the interface to interact with the father in a transparent way.

@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (ListSelectionListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnArticleSelectedListener");
}
}
    • Override the method onListItemClick
Is invoking the father implementation of the method onListItemClick
@Override
public void onListItemClick(ListView l, View v, int pos, long id) {
getListView().setItemChecked(pos, true);
mListener.onListSelection(pos);
}
  • Add the Detail Fragment
    • Create an Array with the options according with each menu in the string.xml file 
    <string-array name="Detail">
        <item>1) Now cracks a noble heart. Good-night, sweet prince; And flights of angels sing thee to thy rest.</item>
        <item>2) As flies to wanton boys, are we to the gods; they kill us for their sport.</item>
        <item>3) There is a tide in the affairs of men, which taken at the flood, leads on to fortune. Omitted, all the voyage of their life is bound in shallows and in miseries.</item>
    </string-array>

    • Create a Layout of type Linear named details_fragment.xml with a TextView inside
<?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="vertical" >

    <TextView
        android:id="@+id/detailsView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="5dip"
        android:textSize="32sp" >
    </TextView>

</LinearLayout>
    • In the MainActivity.java
      • Create a global variable to reference to the Details class
private Details mDetails;
      • Override the method onCreate to get the Fragment of the Details, defined in activity_main.xml
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDetails = (Details) getFragmentManager()
.findFragmentById(R.id.details);
}
      • In the MainActivity.java implements ListSelectionListener that is defined in Menu.java and override the method onListSelection to show the proper detail.
@Override
public void onListSelection(int index) {
if (mDetails.getShownIndex() != index) {
mDetails.showQuoteAtIndex(index);
}
}
    • Create a class named Details and extends Fragments
public class Details extends Fragment{

    • Create a global variable to know the index of the detail that is shown and a method to know the index
private int mCurrIdx = -1;
public int getShownIndex() {
return mCurrIdx;
}

    • Override  the method onActivityCreated to get theTextView created in details_fragment.xml and get the array with the texts
Is a  global variable
private TextView mDetailsView = null;      

@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
mDetailsView = (TextView) getActivity().findViewById(R.id.detailsView);
}
    • Create a method to show the proper detail text.

 public void showQuoteAtIndex(int newIndex) { if (newIndex < 0 || newIndex >= getResources().getStringArray(R.array.Detail).length ) return; mCurrIdx = newIndex; mDetailsView.setText(getResources().getStringArray(R.array.Detail)[mCurrIdx]); }


    • Override the onCreateView method to associated the fragment with the LinearLayout defined in details_fragment.xml

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

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