// when layers are added/removed
private void Layers_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
LayerCollection layers = (LayerCollection)sender;
// Put updating of measurable layers in a throttle timer, meaning that this logic will
// only be invoked once if the CollectionChanged event fires multiple times within two
// tenths of a second. This is necessary because changing to a basemap in a different
// spatial reference results in clearing and rebuilding the layers collection.
if (_updateMeasurableLayersThrottler == null)
{
_updateMeasurableLayersThrottler = new ThrottleTimer(20, () =>
{
// Check whether all layers are initialized
if (layers.Any(l => !l.IsInitialized))
{
layers.LayersInitialized += Layers_LayersInitialized; // Wait for initialization
}
else
{
UpdateMeasurableLayers(); // Update measurable layers collection now
}
});
}
_updateMeasurableLayersThrottler.Invoke();
// Check whether layers were added
if (e.NewItems != null)
{
// Hook into visibility changed events for added layers
foreach (Layer layer in e.NewItems)
{
layer.PropertyChanged += Layer_PropertyChanged;
if (layer is ArcGISDynamicMapServiceLayer)
{
ISublayerVisibilitySupport subLayerSupport = layer as ISublayerVisibilitySupport;
subLayerSupport.VisibilityChanged += SubLayerSupport_VisibilityChanged;
}
}
}
// Check whether layers were removed
if (e.OldItems != null)
{
// Unhook from visibility changed events for removed layers
foreach (Layer layer in e.OldItems)
{
layer.PropertyChanged -= Layer_PropertyChanged;
if (layer is ArcGISDynamicMapServiceLayer)
{
ISublayerVisibilitySupport subLayerSupport = layer as ISublayerVisibilitySupport;
subLayerSupport.VisibilityChanged -= SubLayerSupport_VisibilityChanged;
}
}
}
// If draw layer has been added to the map, check whether it is the top-most
if (layers.Contains(DrawLayer) && layers.IndexOf(DrawLayer) != layers.Count - 1)
{
// Draw layer is not top-most. Move it to the top by removing and re-adding it. Wrap in
// a begin invoke call so the collection is modified outside the CollectionChanged event.
Map.Dispatcher.BeginInvoke(() =>
{
layers.Remove(DrawLayer);
layers.Add(DrawLayer);
});
}
}