Issue with Hide / Remove Overlay Marker on perticular zoom level
<p>I am developing an application in which i have Try Mapforge for Offline map data.i get successfully integrate in the system.i have detect zoom level on change listner and based on level i need to set marker.so i have just write simple code for that ...</p>

<pre><code>@Override
    public void onZoomLevelChanged(int zoomLevel) {
        // TODO Auto-generated method stub
        Log.i("TAG","Zoom Level has change");
        int intZoom = mapView.getMapPosition().getZoomLevel();
         if(intZoom &lt;4)
         {

             if(!mapView.getOverlays().isEmpty()) 
             { 
                 mapView.getOverlays().clear();
                 mapView.invalidate();

                 mapView.getOverlays().remove(mapOverlays);
                 mapView.invalidate();
                 isFirstTimeExecution = false;

             }
         }
         else if( intZoom &gt;4 &amp;&amp; intZoom &lt; 15)
         {
            if(mapView.getOverlays().isEmpty() &amp;&amp; !isFirstTimeExecution) 
             {
                mapView.getOverlays().add(mapOverlays);
                mapView.invalidate();
                isFirstTimeExecution = true;
             }


         }
    }
</code></pre>

<p>//here basically i want to set marker in zoom level 4 to 15 and if zoom level should be less then 4 then it will remove or hide,but here is throw something thread exception dont know why it raised</p>

<p><strong>Error ::</strong></p>

<pre><code>10-11 17:20:40.161: ERROR/AndroidRuntime(5810): FATAL EXCEPTION: main
10-11 17:20:40.161: ERROR/AndroidRuntime(5810): java.lang.IllegalThreadStateException: Thread already started.
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at java.lang.Thread.start(Thread.java:1322)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at org.mapsforge.android.maps.overlay.OverlayList.setupOverlay(OverlayList.java:193)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at org.mapsforge.android.maps.overlay.OverlayList.add(OverlayList.java:53)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at org.mapsforge.android.maps.overlay.OverlayList.add(OverlayList.java:30)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at com.offlinemap.OfflinMapActivity.onZoomLevelChanged(OfflinMapActivity.java:189)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at com.offlinemap.MyMapView.dispatchDraw(MyMapView.java:176)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.View.draw(View.java:6743)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewGroup.drawChild(ViewGroup.java:1640)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.View.draw(View.java:6743)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.widget.FrameLayout.draw(FrameLayout.java:352)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewGroup.drawChild(ViewGroup.java:1640)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewGroup.drawChild(ViewGroup.java:1638)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1367)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.View.draw(View.java:6743)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.widget.FrameLayout.draw(FrameLayout.java:352)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1842)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewRoot.draw(ViewRoot.java:1407)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewRoot.performTraversals(ViewRoot.java:1163)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1727)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.os.Looper.loop(Looper.java:123)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at android.app.ActivityThread.main(ActivityThread.java:4627)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at java.lang.reflect.Method.invokeNative(Native Method)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at java.lang.reflect.Method.invoke(Method.java:521)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-11 17:20:40.161: ERROR/AndroidRuntime(5810):     at dalvik.system.NativeStart.main(Native Method)
</code></pre>
