Ensure BaseDynamicLayer is always the most visible layer

Question

If I add a shapefile to my map and then a dynamic custom layer inherited from a BaseDynamicLayer, then the shapefile is lower on the viewing stack then my custom layer, and it displays correctly.

mapControl.AddShapeFile(directoryPath, shapeFile);
mapControl.AddLayer(dynamicCustomLayer); //this is ok

But if I add my dynamicCustomLayer first, and then add a Shapefile, the shapefile is makes the dynamic layer non viewable because it is higher on the viewing stack...

mapControl.AddLayer(dynamicCustomLayer); 
mapControl.AddShapeFile(directoryPath, shapeFile);//now my dynamic layer is invisible

How can I ensure that the dynamic custom layer is always on top of the viewing stack even if my user adds a shapefile after the custom layer was enabled...

I'm using C# ArcEngine 10

Answer 1

You'll have to keep a reference to your dynamic layer, then just use IMapControl2.MoveLayerTo, which takes a from index and a to index, both 0 based. Smaller numbers draw later, so it sounds like you need to keep this at index 0.

Edit: You don't need a reference to the layer, unless you can't keep track of what index it's on and have to iterate through the Layer collection. Adding a shapefile will automatically put the shapefile at index 0 and promote everything else by 1. If the layer you need to keep on top was at 0 before, you know it's at 1 now. Makes it a bit easier to manage.

See ESRI's documentation for MoveLayerTo.

Answer 2

If you need to catch that the user adds layer you can wire up a ItemAdded event on the active view:

    Private activeViewEvents As ESRI.ArcGIS.Carto.IActiveViewEvents_Event
    Private m_ActiveViewEventsItemAdded As ESRI.ArcGIS.Carto.IActiveViewEvents_ItemAddedEventHandler

    Private Sub AddEventListenerToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles AddEventListenerToolStripMenuItem.Click
        activeViewEvents = CType(axMapControl1.ActiveView.FocusMap, ESRI.ArcGIS.Carto.IActiveViewEvents_Event)

        m_ActiveViewEventsItemAdded = New ESRI.ArcGIS.Carto.IActiveViewEvents_ItemAddedEventHandler(AddressOf OnActiveViewEventsItemAdded)

        AddHandler CType(axMapControl1.ActiveView.FocusMap, ESRI.ArcGIS.Carto.IActiveViewEvents_Event).ItemAdded, m_ActiveViewEventsItemAdded
    End Sub


    Private Sub OnActiveViewEventsItemAdded()
        'makes layer(1) always on top.
        axMapControl1.ActiveView.FocusMap.MoveLayer(axMapControl1.ActiveView.FocusMap.Layer(0), 1)
    End Sub