title: OSMdroid change TileSource at Runtime
body: <p>i working with osmdroid and i want to change the TileSource at runtime (via menu entry). For example i can change between OSM TileSource and GoogleTileSource.</p>
  
  <p>Problem: Everything works fine, but when i change the TileSource while the mapview is loading a Tile in the background, it changes the TileSource but one or two tiles are from the TileSource befor. So i see a mixed MapView with OSMTiles and one or two GoogleTiles.</p>
  
  <p>The tileCache is cleared everytime after changing the TileSource. But the loading tile in the background isnt in the cache at this moment, so he put this tile to the cache, after clearing it. </p>
  
  <p>Any Idea to workaround this issue?? It is all based on osmdroid, i only work with <code>setTileSource(ITileSource)</code></p>
  
  <p>Thanks and Greetz</p>