Android listview custom rows

I have a problem with a custom layout I've set for my listView. I have a button that adds elements to the listView and it uses a custom row but everytime I try to press the button to add it crashes. Can anyone suggest a solution on how to fix this? I'm pretty new to android btw.

Here's the code:

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.ListView;

import java.util.ArrayList;

public class ProjectCreateScreen extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.secondary_layout1);

    Button btn = (Button) findViewById(R.id.addBtn);

    final ArrayList<String> listItems=new ArrayList<String>();
    final ListAdapter addAdapter = new ArrayAdapter<String>(this, R.layout.custom_row,
            listItems);
    ListView lv = (ListView) findViewById(R.id.lv);
    lv.setAdapter(addAdapter);

    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            listItems.add("New Project");
            ((ArrayAdapter) addAdapter).notifyDataSetChanged();
        }
    });
    lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Intent switchToEdit = new Intent(ProjectCreateScreen.this, teamCreateScreen.class);
            startActivity(switchToEdit);
        }
    });
}

}

The layout this activity uses:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/rl">

<Button
    android:layout_width="match_parent"
    android:layout_height="60dp"
    android:text="@string/AddProject"
    android:id="@+id/addBtn"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:onClick="StartProject"/>

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/addBtn"
    android:id="@+id/lv">
    </ListView>

</RelativeLayout>

The custom row layout:

<?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="vertical">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="80dp"
    android:id="@+id/customRow"/>

</LinearLayout>