title: osmdroid displays an empty grid
body: <p>I wanted to try out having OpenStreetMap integration by osmdroid, but I got stuck at an issue where I have no idea what is missing. The scenario is as follows:</p>
  
  <p><strong>Symptom: Map widget gets displayed but only with an empty grid.</strong></p>
  
  <p>This is in my Activity class:</p>
  
  <pre><code>@Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      MapView mapView = new MapView(this, 256);
      mapView.setTileSource(TileSourceFactory.MAPNIK);
      mapView.setClickable(true);
      mapView.setBuiltInZoomControls(true);
      setContentView(mapView);
  }
  </code></pre>
  
  <p>(I tried selecting various TileSources with seemingly no difference)</p>
  
  <p>My Manifest also includes these permissions (as a child of <code>&lt;manifest&gt;</code>, after <code>&lt;uses-sdk&gt;</code>):</p>
  
  <pre><code>&lt;uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /&gt;
  &lt;uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /&gt;
  &lt;uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /&gt;
  &lt;uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /&gt;
  &lt;uses-permission android:name="android.permission.INTERNET" /&gt;
  &lt;uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /&gt;
  </code></pre>
  
  <p>...and my emulator is otherwise connected to the internet, eg. web browsers work.</p>
  
  <p>osmdroid and slf4j are in the build path. The app compiles without a problem and generates no exceptions.</p>
  
  <p>What could be wrong?</p>
  
  <p>Many thanks!</p>
  
  <p><strong>SOLVED: This was caused by my emulator not having an external storage to cache map tiles.</strong> </p>