return(convertView);
}
Here, getView() receives three parameters:
• The index of the item in the array to show in the view
• An existing view to update with the data for this position (if one already existed, such as from scrolling — if null, you need to instantiate your own)
• The widget that will contain this view, if needed for instantiating the view
In the previous example, the adapter still returns a TextView, but uses a different behavior for determining the string that goes in the view. Chapter 9 will cover fancier ListViews.
Other Key Adapters
Here are some other adapters in Android that you will likely use:
• CursorAdapter converts a Cursor, typically from a content provider, into something that can be displayed in a selection view
• SimpleAdapter converts data found in XML resources
• ActivityAdapter and ActivityIconAdapter provide you with the names or icons of activities that can be invoked upon a particular intent
Lists of Naughty and Nice
The classic listbox widget in Android is known as ListView. Include one of these in your layout, invoke setAdapter() to supply your data and child views, and attach a listener via setOnItemSelectedListener() to find out when the selection has changed. With that, you have a fully-functioning listbox.
However, if your activity is dominated by a single list, you might well consider creating your activity as a subclass of ListActivity, rather than the regular Activity base class. If your main view is just the list, you do not even need to supply a layout — ListActivity will construct a full-screen list for you. If you do want to customize the layout, you can, so long as you identify your ListView as @android:id/list, so ListActivity knows which widget is the main list for the activity.
For example, here is a layout pulled from the Selection/List sample project. This sample along with all others in this chapter can be found in the Source Code area of http://apress.com.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView
android:id="@+id/selection"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
<ListView
android:id="@android:id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:drawSelectorOnTop="false"
/>
</LinearLayout>
It is just a list with a label on top to show the current selection.
The Java code to configure the list and connect the list with the label is:
public class ListViewDemo 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 ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1,
items));
selection=(TextView)findViewById(R.id.selection);
}
public void onListItemClick(ListView parent, View v, int position,
long id) {
selection.setText(items[position]);
}
}
With ListActivity, you can set the list adapter via setListAdapter() — in this case, providing an ArrayAdapter wrapping an array of nonsense strings. To find out when the list selection changes, override onListItemClick() and take appropriate steps based on the supplied child view and position (in this case, updating the label with the text for that position).
The results are shown in Figure 8-1.
Figure 8-1. The ListViewDemo sample application
Spin Control
In Android, the Spinner is the equivalent of the drop-down selector you might find in other toolkits (e.g., JComboBox in Java/Swing). Pressing the center button on the D-pad pops up a selection dialog for the user to choose an item from. You basically get the ability to select from a list without taking up all the screen space of a ListView, at the cost of an extra click or screen tap to make a change.
As with ListView, you provide the adapter for data and child views via setAdapter() and hook in a listener object for selections via setOnItemSelectedListener().
If you want to tailor the view used when displaying the drop-down perspective, you need to configure the adapter, not the Spinner widget. Use the setDropDownViewResource() method to supply the resource ID of the view to use.
For example, culled from the Selection/Spinner sample project, here is an XML layout for a simple view with a Spinner:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView
android:id="@+id/selection"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
<Spinner android:id="@+id/spinner"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:drawSelectorOnTop="true"
/>
</LinearLayout>
This is the same view as shown in the previous section, just with a Spinner instead of a ListView. The Spinner property android:drawSelectorOnTop controls whether the arrows are drawn on the selector button on the right side of the Spinner UI.