自定义listview的ArrayAdapter报空指针,该怎么解决

<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:orientation="vertical"
    tools:context=".ListViewTest" >

    <TextView
        android:id="@+id/txtselection"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" >
    </TextView>

    <ListView
        android:id="@android:id/list"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:drawSelectorOnTop="false"
        android:orientation="vertical" >
    </ListView>

</LinearLayout>

<?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="horizontal" >

    <ImageView
        android:id="@+id/icon"
        android:layout_width="22dp"
        android:layout_height="wrap_content"
        android:paddingLeft="2dp"
        android:paddingRight="2dp"
        android:paddingTop="2dp"
        android:src="@drawable/ok" />

    <TextView
        android:id="@+id/label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="44sp" />

</LinearLayout>

public class ListViewTest extends ListActivity {

    TextView selection;
    String[] items = {
            "Apple", "orange", "Banana", "peach", "Grape", "Strawberry", "matermelon", "lemon"
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_view_test);
        //setContentView(R.layout.list_vew_test_row);
        // setListAdapter(new ArrayAdapter<String>(this,
        // android.R.layout.simple_list_item_1, items));
        setListAdapter(new IconicAdapter());

        selection = (TextView)findViewById(R.id.txtselection);
        selection.setText("Please select");
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.list_view_test, menu);
        return true;
    }

    public void onListItemClick(ListView parent, View v, int position, long id) {

        selection.setText(items[position]);
    }

    class IconicAdapter extends ArrayAdapter {
        IconicAdapter() {
            super(ListViewTest.this, R.layout.list_vew_test_row, items);
        }

        public View getView(int position, View convertView, ViewGroup parent) {