Beginning Android

• android:spacing controls the number of pixels between entries in the list.

• android:spinnerSelector controls what is used to indicate a selection — this can either be a reference to a Drawable (see the resources chapter) or an RGB value in #AARRGGBB or similar notation.

• android:drawSelectorOnTop indicates if the selection bar (or Drawable) should be drawn before (false) or after (true) drawing the selected child — if you choose true, be sure that your selector has sufficient transparency to show the child through the selector, otherwise users will not be able to read the selection.

CHAPTER 9 Getting Fancy with Lists

The humble ListView is one of the most important widgets in all of Android, simply because it is used so frequently. Whether choosing a contact to call or an email message to forward or an ebook to read, ListView widgets are employed in a wide range of activities. Of course, it would be nice if they were more than just plain text.

The good news is that they can be as fancy as you want, within the limitations of a mobile device’s screen, of course. However, making them fancy takes some work and some features of Android that I will cover in this chapter.

Getting to First Base

The classic Android ListView is a plain list of text — solid but uninspiring. This is because all we hand to the ListView is a bunch of words in an array, and we tell Android to use a simple built-in layout for pouring those words into a list.

However, you can have a list whose rows are made up of icons, or icons and text, or checkboxes and text, or whatever you want. It is merely a matter of supplying enough data to the adapter and helping the adapter to create a richer set of View objects for each row.

For example, suppose you want a ListView whose entries are made up of an icon, followed by some text. You could construct a layout for the row that looks like this, found in the FancyLists/Static sample project available in the Source Code section of the Apress Web site:

<?xml version='1.0' encoding='utf-8'?>
<LinearLayout xmlns:android='http://schemas.android.com/apk/res/android'
 android:layout_width='fill_parent'
 android:layout_height='wrap_content'
 android:orientation='horizontal'>
 <ImageView
  android:id='@+id/icon'
  android:layout_width='22px'
  android:paddingLeft='2px'
  android:paddingRight='2px'
  android:paddingTop='2px'
  android:layout_height='wrap_content'
  android:src='@drawable/ok'
 />
 <TextView
  android:id='@+id/label'
  android:layout_width='wrap_content'
  android:layout_height='wrap_content'
  android:textSize='44sp'
 />
</LinearLayout>

This layout uses a LinearLayout to set up a row, with the icon on the left and the text (in a nice big font) on the right.

By default, though, Android has no idea that you want to use this layout with your ListView. To make the connection, you need to supply your Adapter with the resource ID of the custom layout shown in the preceding code:

public class StaticDemo extends ListActivity {
 TextView selection;
 String[] items={'lorem', 'ipsum', 'dolor', 'sit', 'amet',
  'consectetuer', 'adipiscing', 'elit', 'morbi', 'vel',
  'ligula', 'vitae', 'arcu', 'aliquet', 'mollis',
  'etiam', 'vel', 'erat', 'placerat', 'ante',
  'porttitor', 'sodales', 'pellentesque', 'augue',
  'purus'};
 @Override
 public void onCreate(Bundle icicle) {
  super.onCreate(icicle);
  setContentView(R.layout.main);
  setListAdapter(new ArrayAdapterString (this,
   R.layout.row, R.id.label, items));
  selection = (TextView)findViewById(R.id.selection);
 }
 public void onListItemClick(ListView parent, View v,
  int position, long id) {
  selection.setText(items[position]);
 }
}

This follows the general structure for the previous ListView sample.

The key in this example is that you have told ArrayAdapter that you want to use your custom layout (R.layout.row) and that the TextView where the word should go is known as R.id.label within that custom layout. Remember: to reference a layout (row.xml), use R.layout as a prefix on the base name of the layout XML file (R.layout.row).

The result is a ListView with icons down the left side. In particular, all the icons are the same, as Figure 9-1 shows.

Figure 9-1. The StaticDemo application