自定义WP插件和表单处理

Hi thats is my first post and please don't kill me :D So, I work on my custom WP plugin. The plugin simple fetch data from one XML file and display it in widget area. Now I want to let the Administrator to choose a data source (simple form like this:

admin-page.php

<h3> Please select a data source </h3>
<form method ="post" action="#">
<select name="Data source">
  <option value="news1">Data source 1</option>
  <option value="news2">Data source 2</option>
  <option value="news3">Data source 3</option>
</select>
<input type="hidden" name="action" value="Specifed url goes here ?" />
<input type="submit">
</form>

All functionality of the widget is stored in my-widget-functions.php

$url='http://mydatasource/xyz?';
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_URL,$url);
$result=curl_exec($ch);
curl_close($ch);
.........
convert->xml;/

Here is my question. I want to change the data source based on user(admin) input, in my case that means the variable $url stored in my-widget-functions.php. Some suggestions, how to do that? Change a variable in another file, based on user input?

I tried to pass the user input between this 2 files with sessions, but it doesn't work. Actually, in that way, the user input was not stored in the WP-DB.