 <p>Is <code>onClick()</code> supposed to be an event handler for a button click? If so, the signature is wrong.</p> <p>I believe you are looking for something like this. I have changed it from an ArrayList to a generic List. And initialized it with a collection initializer, and made it accessible from within your function. Please run the code below and let us know if you get exceptions.</p> <pre><code>List&lt;string&gt; MyList=new List&lt;string&gt;() {"Android", "Blackberry", "Hardcore"}; public void onClick(View view) { MyList.Add("testing"); adapter.notifyDataSetChanged(); } </code></pre>