public synchronized void destroy() {
        if (this.mapWriter != null) {
            this.mapWriter.destroy();
            this.mapWriter = null;
        }
        this.providerLayer = null;
    }
Destroys this layer and cleans up any resouces held by it. Do not use this object again
after calling destroy()!
main/src/main/java/cgeo/geocaching/unifiedmap/geoitemlayer/GeoItemLayer.java