How to get a Layer as ILayer (ArcObjects)

Question

I had asked this question previously which I think will work. But as I am new to this, I can't figure out how to get a Layer as an ILayer object to pass to the method that's in my previous questions answer.

I have been playing with the Mark Cederholm's 'Snippets.py' that uses comtypes to drive ArcObjects. That works well, but I don't know enough to venture far from the examples given. It first gets an IMxApplication object, and I can't figure out how to get a Layer file as an ILayer from this object so that I can use the script I was shown in my previous question.

In the end I want to be able to change the Display Expression of some Table Views, and be able to grab them by their name in the TOC.

Note: If you know how to do this with C# or VBA, I can figure it out in Python

Update: Here is the answer in Python which relies on Mark Cederholm's Snippets.py and comtypes:

from Snippets import *
GetDesktopModules()
import comtypes.gen.esriCarto as esriCarto
import comtypes.gen.esriArcMapUI as esriArcMapUI
InitStandalone()
pApp = GetApp()
pMxDoc = CType(pApp.Document, esriArcMapUI.IMxDocument)
pFeatureLayer = CType(pMxDoc.FocusMap.Layer(0), esriCarto.IFeatureLayer) 

Answer 1

You need to access the active document in order to get access to layers. Create a reference to the document using your IMxApplication object (pMxApp):

Dim pMxDoc as IMxDocument = pMxApp.Document

Then access layers through focusmap:

Dim pLayer as ILayer = pMxDoc.FocusMap.Layer(i)

Where "i" is the index of your layer.

Answer 2

You can use IMapDocument interface. In my code snippetarcgis102.py it is Mark Cederholm's 'Snippets.py'

pMapDocument = snippetarcgis102.NewObj(esriCarto.MapDocument,esriCarto.IMapDocument)
pMapDocument.open(path) #like pDoc
pMap = pMapDocument.Map(0)
pEnumLayer = pMap.Layers(None,True)
#key = name of layer from gdb (en UPPER CASE) value =ptr to IGeoFeatureLayer layers (not group layers)
layer_ptr_dict={} 

pLayer = pEnumLayer.Next()
while pLayer: 
  pGeoFeatureLayer = snippetarcgis102.CType(pLayer,esriCarto.IGeoFeatureLayer)   
  if pGeoFeatureLayer: # list of IGeofeature layers (not group layers)
    en_name = pGeoFeatureLayer.FeatureClass.AliasName.encode('utf-8') # name in GDB, not in TOC
    layer_ptr_dict [en_name] = pGeoFeatureLayer 
  else: # else it is group layer and we collapse it 
    group_layer =  snippetarcgis102.CType(pLayer,esriCarto.IGroupLayer)
    group_layer.Expanded = False #collapse group layers  
  pLayer = pEnumLayer.Next()