无法从php页面接收JSON对象

Question

我有一个非常简单的PHP代码：

<?php
$myArr = array("John", "Mary", "Peter", "Sally");
echo json_encode($myArr);
?>

在我的android工作室中我有以下asynctask类，它将产生一个名为result的字符串：

public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
    @Override
    protected Boolean doInBackground(Void... params) {
        try {
            result = HttpManager.SendData(dataPack);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return true;
    }

    @Override
    protected void onPostExecute(final Boolean success) {
            Toast.makeText(c,result,Toast.LENGTH_SHORT).show();
        mAuthTask = null;
    }

    @Override
    protected void onCancelled() {
        mAuthTask = null;
    }
}

使用结果字符串类的jsonparser如下：

private String[] jSonParser(String s){
    String[] mlist={""};
    mlist[0]="no users found";
    if (s != null) {
        try {
            JSONObject o = new JSONObject(result);
            JSONArray a = o.getJSONArray("types");
            for (int i = 0; i < a.length(); i++) {
                mlist[i]=a.getString(i);
            }
            Toast.makeText(c, "JSON recieved!", Toast.LENGTH_SHORT).show();
        } catch (JSONException e) {
            e.printStackTrace();
            Toast.makeText(c, "JSONException", Toast.LENGTH_SHORT).show();
        }
    }
    else {
        Toast.makeText(c, "Couldn't get any JSON data.", Toast.LENGTH_SHORT).show();
    }
    return mlist;
}

但我一直得到JSONException。我做错了什么？