ASyncTask and returning an ArrayList

Im trying to return an ArrayList from the AsyncTask class back to the MainAcitivity class and then use this arraylist to fill the gridview in MainActivity.

The parseURL takes a String paramater to parse the url. And parseURL is executed when the user clicks the button. The code i have compiles and run but the gridview is not populated after triggering the button event, and pressing the button twice crashes the app.

Here is my code for MainActivity:

private List<String> list = new ArrayList<String>();

public void setList(List<String> list) { this.list = list; }

public void onButtonClick(View v) {
    EditText textInput = (EditText)findViewById(R.id.editText1);
    String code = textInput.getText().toString();

    new parseURL(this).execute(code);

    //use the list from parseURL to fill grid view
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, list);

    gridView.setAdapter(adapter);
    adapter.notifyDataSetChanged();
}

ParseURL class

public class parseURL extends  AsyncTask<String, Void, List<String>> {
List<String> str;
private MainActivity act;

public parseURL(MainActivity act) {
    this.act = act;
}

protected List<String> doInBackground(String... params) {
    try {
        Document doc = Jsoup.connect("http://ift.tt/1wlNI8G" + params).get();

        Elements row1 = doc.select("table");
        Elements row2 = doc.select("td");
        Elements row3 = doc.select("td");

        for (int i = 0; i < row1.size(); i++) {
            str.add(row1.get(i).text() + "," + row2.get(i).text() + "," + row2.get(i).text());
        }
        return str;
        }
    catch() {
    }

    protected void onPostExecute(List<String> str) {
        act.setList(str)
    }
}