title: Access to the path denied when trying to create a file on external storage
body: <p>I want my android app to save a text file with the contents from an <code>EditText</code>. When I do as follows, the new files are saved as expected:</p>
  
  <pre><code>string[] filename = new string[50];
  EditText et1 = FindViewById&lt;EditText&gt;(Resource.Id.editText1);
  EditText et2 = FindViewById&lt;EditText&gt;(Resource.Id.editText2);
  string doc = Android.OS.Environment.ExternalStorageDirectory.AbsolutePath;
  filename[0] = Path.Combine(doc, "Text1");
  filename[1] = Path.Combine(doc, "Text2");
  File.WriteAllText(filename[0], et1.Text);
  File.WriteAllText(filename[1], et2.Text);
  </code></pre>
  
  <p>But if I change the filename as follows: </p>
  
  <pre><code>filename[0] = Path.Combine(doc, 1.ToString());
  filename[1] = Path.Combine(doc, 2.ToString());
  </code></pre>
  
  <p>The app will combine the determined address but it can not write data there and throws the following exception:</p>
  
  <pre><code>Error: Access to this address denied
  </code></pre>
  
  <p>How I can solve this problem?</p>