Android ListActivity sorting

Question : how to sort on a given Android ListActivity column ?

Answer :
- attach a setOnClickListener to its corresponding TextView instance
- think about the Comparator interface
- after comparison, call notifyDataSetChanged on your list view adapter


Details :

Step #1 : Layout definition :

<LinearLayout
    android:layout_marginTop="10dip"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_marginRight="10dip"
    android:layout_marginLeft="10dip"
    android:background="@drawable/background">
    <TextView
        android:id="@+id/cName"
        android:textColor="@drawable/black"
        android:layout_width="0dip"
        android:layout_weight="46"
        android:layout_height="25dip"
        android:text="@string/bdle_name"
        android:gravity="center"
        />
    <TextView
        ...
        />
    <TextView
        ...
        />
</LinearLayout>
<ListView
    android:id="@+id/android:list"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:scrollbars="verticalhorizontal"
    android:layout_marginRight="15dip"
    android:layout_marginLeft="15dip"
    android:layout_marginTop="5dip"
    />

Step #2 : given the BundleInfo class that holds the different attributes/columns of the list to be displayed, attach the listener to the TextView column subject to sorting, here : cName

public final class RestClient extends ListActivity
{
    /**
     * Bundles list
     */
    private ArrayList<BundleInfo> bundles = new ArrayList<BundleInfo>();

    /**
     * List view adapter
     */
    private CustomAdapter adapter = null;

    /**
     * list sorting type
     */
    private SortType sortType = SortType.NONE;

    /**
     * Sorting order (-1 if reversed)
     */
    private int sign = 1;

    /**
     * Name column widget
     */
    private TextView cName = null;

    /**
     * Enumerated type for column sorting
     */
    private enum SortType
    {NAME,        // by 'Name'
     // OTHER,    // by 'Other' column
     NONE}
  
    /**
     * List refresh handler
     */
    private Runnable refresh = new Runnable()
    {

        @Override
        public void run()
        {
            // refresh your list here
            // ...
      
            if (!bundles.isEmpty())
            switch (sortType)
            {
                case NAME:
                    comp = new SortByName();
                    Collections.sort(bundles, comp);
                    break;
          
                // other cases as needed
          
                default:
                    break;
            }
            else sortType = SortType.NONE;
            adapter.notifyDataSetChanged();
        }
    };

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        // Setting activity content
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
  
        // Other initializations
        // ...
        adapter  = new CustomAdapter(this, R.layout.main, R.id.name, bundles);
        setListAdapter(adapter);

        // Sorting
        sortType = SortType.NONE;
        cName = (TextView) findViewById(R.id.cName);
        cName.setOnClickListener(new ImageButton.OnClickListener()
        {
            public void onClick(View v)
            {
                sign = ((sortType == SortType.NAME) ? sign * -1 : sign);
                sortType = SortType.NAME;
                if (!isRunning) runOnUiThread(refresh);
            }
        });
    }

    /**
     * List view adapter
     */
    private final class CustomAdapter extends ArrayAdapter<BundleInfo>
    {
        // List view adapter class body
        // ...
    }
}

The 'refresh' thread being responsible for refreshing the view whenever needed.


Step #3 : for each column you wish to apply a sorting, add such an inner class definition :

/**
 * List comparator for sorting by 'name'
 */
private final class SortByName implements Comparator<BundleInfo>
{
    public int compare(BundleInfo i1, BundleInfo i2)
    {
        return i1.getBundleName().compareTo(i2.getBundleName()) * sign;
    }
}