Android: failed to setContentView when switching to ListActivity

Question

[update] I got the error, which says "Your content must have a ListView whose id attribute is 'android.R.id.list'". Appearently nothing in my xml is ListView. But is that required?

This is an follow-up issue on my previous question android: which view should I use for showing text and image?

I read the article about creating ListView for LinearLayout. However, my following code failed at the setContentView() function when I changed "extends Activity" to "extends ListActivity", any idea why?

private TextView mSelection;
//private ImageView mImages;
static final String[] keywords = new String[]{"China", "Japan", "USA", "Canada"};
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.contactLayout);

    mSelection = (TextView)findViewById(R.id.ContactNames);
    ArrayAdapter adapter = new ArrayAdapter<String>(this, R.layout.contactlayout, R.id.ContactNames,keywords);
    setListAdapter(adapter);
    }

My Layout is from this article: http://www.curious-creature.org/2009/02/22/android-layout-tricks-1/

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="?android:attr/listPreferredItemHeight"

android:padding="6dip">

<ImageView
    android:id="@+id/icon"

    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:layout_marginRight="6dip"

    android:src="@drawable/icon" />

<LinearLayout
    android:orientation="vertical"

    android:layout_width="0dip"
    android:layout_weight="1"
    android:layout_height="fill_parent">

    <TextView
        android:id="@+id/ContactNames"
        android:layout_width="fill_parent"
        android:layout_height="0dip"
        android:layout_weight="1"

        android:gravity="center_vertical"
        android:text="My Application" />

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="0dip"
        android:layout_weight="1" 

        android:singleLine="true"
        android:ellipsize="marquee"
        android:text="Simple application that shows how to use RelativeLayout" />

</LinearLayout>

Answer 1

I think you misunderstood the other posts I showed you in the previous question. They were explaining how to use a custom layout for each row in your list, not how to define the entire layout file for the activity. You need something like this:

(main.xml)
<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:cacheColorHint="#00000000"
    android:id="@android:id/list">
</ListView>

Note the very important line android:id="@android:id/list". You must have that in your ListView as that's what tells Android where your list is. The cacheColorHint is useful if your background isn't black - see this post for more details about that.

With the above lines you can give your activity a list that will be recognised properly. Here's a basic example:

public class TestProject extends ListActivity {

    final static String[] ITEMS = {"blah", "floop", "gnarlp", "stuff"};

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                R.layout.listrow, R.id.textview, ITEMS);
        setListAdapter(adapter);
    }
}

Then the listrow layout is just this:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <TextView android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/textview"/>
</LinearLayout>

This is a really simple layout. If you want to get something more complicated, changes are you'll have to use a BaseAdapter, as that gives you calls getView(...) before each row. In that you can use different layouts depending on the contents of each row. However, BaseAdapter looks scary when you first try it, so be warned! :)